ARC FLASH STUDIES - Murdoch University · Feeder The first downstream protection device relative to...
Transcript of ARC FLASH STUDIES - Murdoch University · Feeder The first downstream protection device relative to...
ARC FLASH STUDIES An Internship with Fortescue Metals Group
Limited
SCHOOL OF ENGINEERING AND INFORMATION TECHNOLOGY
CHRISTIAN BARABONA BACHELOR OF ENGINEERING
(ELECTRICAL POWER AND INDUSTRIAL COMPUTER SYSTEMS)
JANUARY 2016
Disclaimer
I declare the following work to be my own, unless otherwise referenced, as defined by Murdoch University’s Plagiarism and Collusion Assessment Policy.
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Abstract
A significant safety risk to electrical personnel working on an energised switchboard is the hazard
of exposure to arc flash, which has gained increasing attention over the past decade. Although
reported arc flash injuries are infrequent compared to other electrical injuries, especially electric
shock, the very high costs associated with these arc flash injuries make them one of the most
important categories to avoid in an industrial workplace.
The main objective of this project is to conduct arc flash studies for switchboards installed at
Fortescue’s Solomon Hub to quantify the existing arc flash hazard posed by this type of equipment.
The aim of the study is to find feasible solutions to reduce arc flash incident energy to less than 8
cal/cm2 and to provide appropriate arc flash PPE recommendations.
Switchboards with voltage levels of 0.4kV, 0.69kV, 6.6kV, 11kV and 33kV were investigated. The
arc flash calculations were conducted using the IEEE 1584-2002 Standard, IEEE Guide for
Performing Arc-Flash Hazard Calculations. The study found that many switchboards have dangerous
incident energy levels that must be reduced, in order to allow energised work on the equipment. To
mitigate the hazard, three simple solutions were proposed: optimise protection settings, install
maintenance switches and remote operation.
Firstly, optimising protection settings is the least expensive solution to reduce the operating time of
protection devices, and hence limit arc flash incident energy exposure. Secondly, where a permanent
setting will violate the grading requirement of the system, then installing maintenance switches is
proposed. Thirdly, where the first two strategies cannot be implemented because they will violate
the grading requirement of the system, then remote operation is proposed. This will eliminate the arc
flash hazard because personnel will operate the equipment outside the arc flash boundary.
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If the recommendations of this study are implemented, the arc flash incident energy of the
switchboards will significantly reduce to not greater than 8 cal/cm2. The implications are improved
safety for personnel, given that energy levels on many switchboards currently pose a significantly
higher arc flash hazard.
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Acknowledgements
Firstly, I would like to thank FMG’s engineering team especially my industry supervisors; Lead
Electrical Engineer Brad Mcleod and Principal Electrical Engineer Cobus Strauss for giving me the
opportunity to undertake an engineering internship as part of their team. The support and guidance
that you have provided is much appreciated and the knowledge I have gained from all of you is
invaluable.
I would also like to express my gratitude to my academic supervisors; Dr Sujeewa Hettiwatte and
Dr Gregory Crebbin for their academic assistance, not only for the internship project but also for the
support they have provided throughout my degree at Murdoch University. I would also like to
acknowledge the rest of the staff at the School of Engineering for facilitating our learning and guiding
us throughout our university studies.
Furthermore, I would like to thank my fellow students for making my time at university enjoyable
and for contributing to my academic and professional development.
Most importantly, I would like to thank my family for their unwavering support and encouragement.
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Table of Contents Abstract ............................................................................................................................................iii
Acknowledgements .......................................................................................................................... v
List of Figures ................................................................................................................................. viii
List of Tables .................................................................................................................................... ix
Definitions, Acronyms and Terms Used in this Thesis Report .......................................................... xi
List of symbols ................................................................................................................................. xii
1 Introduction ............................................................................................................................. 1
2 Background .............................................................................................................................. 3
2.1 Engineering Internship ..................................................................................................... 3
2.2 Fortescue Metals Group ................................................................................................... 3
2.2.1 Solomon Hub ............................................................................................................ 4
2.3 Project Background .......................................................................................................... 5
2.4 Arc flash ............................................................................................................................ 7
2.5 Arc flash reported incidents and statistics ........................................................................ 9
2.5.1 Standards and WHS Requirements ......................................................................... 10
2.6 Arc Flash Studies............................................................................................................. 13
2.6.1 NFPA 70E ................................................................................................................ 14
2.6.2 IEEE Std 1584 – 2002 .............................................................................................. 15
2.7 Assumptions and Clarifications ...................................................................................... 16
2.8 PowerFactory ................................................................................................................. 16
3 Methodology .......................................................................................................................... 17
3.1 System audit, data collection and power system modelling .......................................... 17
3.2 Short-Circuit Study ......................................................................................................... 18
3.2.1 Effect of motor contributions in the calculations ................................................... 19
3.3 Arc current calculations .................................................................................................. 21
3.4 Coordination studies ...................................................................................................... 23
3.5 Incident energy and arc flash boundary calculations ..................................................... 24
3.6 PPE selection .................................................................................................................. 26
3.7 Process flowchart ........................................................................................................... 27
4 Results .................................................................................................................................... 28
4.1 Stockyard ........................................................................................................................ 28
4.2 Firetail ............................................................................................................................ 29
4.3 Kings Valley..................................................................................................................... 30
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4.4 RMUs + other attached switchboards ............................................................................ 31
5 Discussion ............................................................................................................................... 32
5.1 Elimination ..................................................................................................................... 36
5.2 Substitution .................................................................................................................... 36
5.3 Engineering Controls ...................................................................................................... 37
5.3.1 Optimise protection settings .................................................................................. 37
5.3.2 Installing a maintenance switch ............................................................................. 37
5.3.3 Zone Selective Interlocking Scheme ....................................................................... 38
5.3.4 Remote Operation .................................................................................................. 39
5.4 Administrative control .................................................................................................... 40
5.5 PPE ................................................................................................................................. 40
6 Recommendations ................................................................................................................. 41
7 Conclusion .............................................................................................................................. 44
8 References.............................................................................................................................. 46
9 Appendices ............................................................................................................................. 49
9.1 Appendix A – Solomon Interconnection diagram ........................................................... 49
9.2 Appendix B – LV incomers Settings................................................................................. 50
9.3 Appendix C – Arc flash study results for the Stockyard .................................................. 53
9.4 Appendix D – Arc flash study results for Firetail OPF...................................................... 54
9.5 Appendix E – Arc flash study results for Kings Valley OPF .............................................. 56
9.6 Appendix F – Arc flash study results for RMUs and switchboards downstream ............. 59
9.7 Appendix G – GE LV circuit breaker curve ...................................................................... 61
9.8 Appendix H – Maintenance mode protection settings ................................................... 62
9.9 Appendix I – Arc flash study results for Stockyard based on the proposed solutions ..... 63
9.10 Appendix J – Arc flash study results for the Firetail OPF based on the proposed solutions
65
9.11 Appendix K – Arc flash study results for the Firetail OPF based on the proposed
solutions ..................................................................................................................................... 67
9.12 Appendix L – Arc flash study results for RMUs based on proposed solutions ................ 69
9.13 Appendix M – Proposed protection settings to resolve grading problems found .......... 71
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List of Figures Figure 1: Fortescue Metals Group Limited Operations Map [1]....................................................... 4
Figure 2: Switchboard installed in Substation 2 ............................................................................... 6
Figure 3: Locations within a switchboard where arc faults can occur: a) outgoing terminal of the
feeder, b) feeder, c) distribution bus, d) main busbar and e) incomer or incoming cable termination.
(Redrawn from [23]) ...................................................................................................................... 12
Figure 4: Fault simulation showing motor contributions ................................................................ 21
Figure 5: TCC illustrating the significant increase in incident energy for a 10% arc current
reduction ........................................................................................................................................ 22
Figure 6: TCC illustrating the effect of the clearing characteristics of a protection relay on the
incident energy ............................................................................................................................... 24
Figure 7: Flow chart which illustrate the steps conducted to achieve the goals of the arc flash
studies ............................................................................................................................................ 27
Figure 8: Fault simulation showing the faulted switchboard .......................................................... 32
Figure 9: Hierarchy of controls (redrawn from [40]) ...................................................................... 36
Figure 10: Zone selective interlocking ........................................................................................... 39
Figure 11: GE LV circuit breaker curve (approval pending [39] .................................................... 61
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List of Tables Table 1: Definitions, acronyms and terms used in this report ........................................................... xi
Table 2: Limitations of equations from IEEE 1584 ........................................................................ 15
Table 3: Distance factors and typical conductor gaps used for the arc flash calculations [30] ....... 22
Table 4: PPE requirements based on incident energy exposure [26] .............................................. 26
Table 5: Arc flash study results for switchboards installed at the Stockyard .................................. 28
Table 6: Arc flash study results for switchboards installed at Firetail OPF .................................... 29
Table 7: Arc flash study results for switchboards installed at Kings Valley OPF........................... 30
Table 8: Arc flash study results for RMUs and loads fed from the RMUs ..................................... 31
Table 9: Existing Stockyard .4 kV MCC protection settings .......................................................... 50
Table 10: Existing Firetail .4 kV MCC protection settings............................................................. 50
Table 11: Existing KV .4 kV MCC protection settings .................................................................. 51
Table 12: 0.4kV MCCs fed from RMUs ........................................................................................ 51
Table 13: Exising incomer protection settings for VSDs ................................................................ 52
Table 14: Arc flash study results for 0.4kV switchboards installed at the Stockyard based on the
existing protection settings ............................................................................................................. 53
Table 15: Arc flash study results for 11kV switchboards installed at the Stockyard based on the
existing protection settings ............................................................................................................. 53
Table 16: Arc flash study results for 0.4kV switchboards installed at Firetail OPF based on the
existing protection settings ............................................................................................................. 54
Table 17: Arc flash study results for 6.6kV switchboards installed at Firetail OPF based on the
existing protection settings ............................................................................................................. 54
Table 18: Arc flash study results for 33kV switchboards installed at Firetail OPF based on the
existing protection settings ............................................................................................................. 55
Table 19: Arc flash study results for 0.4kV switchboards installed at KV OPF based on the existing
protection settings .......................................................................................................................... 56
Table 20: Arc flash study results for the 6.6kV switchboards installed at KV OPF based on the
existing protection settings ............................................................................................................. 57
Table 21: Arc flash study results for 33kV switchboards installed at KV OPF based on the existing
protection settings .......................................................................................................................... 58
Table 22: Arc flash study results for the RMUs based on the existing settings .............................. 59
Table 23: Arc flash study results for the sizer drives switchboards based on the existing protection
settings ........................................................................................................................................... 59
Table 24: Arc flash study results for the VSDs based on the existing protection settings .............. 59
Table 25: Arc flash study results for 0.4kV switchboards based on the existing protection settings
....................................................................................................................................................... 60
Table 26: Settings and location of the three maintenance switches ................................................ 62
Table 27: Arc flash study results for 0.4kV switchboards installed at the Stockyard based on the
proposed protection settings ........................................................................................................... 63
Table 28: Proposed protection settings for the Stockyard 0.4kV switchboards incomers ............... 63
Table 29: Arc flash study results for the Stockyard 11kV switchboards based on the proposed
protection settings .......................................................................................................................... 63
Table 30: Proposed protection settings for Stockpile 11kV switchboards incomers....................... 64
Table 31: Arc flash study results for Firetail 0.4kV switchboards based on the proposed protection
settings ........................................................................................................................................... 65
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Table 32: Proposed protection settings for Firetail 0.4kV switchboards incomers ......................... 65
Table 33: Arc flash study results for Firetail 33kV switchboards based on the proposed
maintenance mode protection settings ............................................................................................ 66
Table 34: Arc flash study results for KV 0.4kV switchboards based on the proposed protection
settings ........................................................................................................................................... 67
Table 35: Proposed protection settings for KV 0.4kV incomer ...................................................... 68
Table 36: Arc flash study results for KV 33kV switchboards based on the proposed maintenance
mode protection settings................................................................................................................. 68
Table 37: Arc flash study results for the RMUs based on the proposed maintenance mode
protection settings .......................................................................................................................... 69
Table 38: Arc flash study results for 0.4kV switchboards based on the proposed protection settings
....................................................................................................................................................... 69
Table 39: Proposed protection settings for LV incomers ................................................................ 70
Table 40: Proposed settings for protection devices for the main Firetail 33kV switchboard (2000-
SR001) ........................................................................................................................................... 71
Table 41: Proposed settings for protection devices for the main KV 33kV switchboard (2000-
SR001) ........................................................................................................................................... 71
Table 42: Proposed settings for feeders to RMUs for correct coordination between protection
devices ........................................................................................................................................... 71
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Definitions, Acronyms and Terms Used in this Thesis Report
Table 1: Definitions, acronyms and terms used in this report
A Amperes
AC Alternating Current
Arc fault
current A fault current flowing through ionized air during an arc flash event
Bolted fault
current
A short-circuit or electrical contact between conductors at different voltages in
which the impedance between the conductors is close to zero
Cal Calories
CB Circuit Breaker
cm Centimetre
DOL Direct On Line
Feeder The first downstream protection device relative to the main busbar
FLA Full Load Amps
Grading Correct coordination between protection devices
HV High Voltage (greater than or equal 1kV)
IAC Internal Arc Classification
Instantaneous
function Protection element of low voltage circuit breakers that has no intentional delay
Incomer First upstream protection device relative to the main busbar
kA Kilo Amperes
kV Kilo Volts
KV Kings Valley
Long time
function Inverse-time overcurrent element of low voltage circuit breakers
LV Low Voltage (less than 1kV)
MCC Motor Control Centre
MS Maintenance Switch
MPU Mobile Power Unit
Operating time Total time taken by a protection device to initiate trips or alarms exclusive of any time
delays inherent in the tripping circuit after a trip is initiated
OPF Ore Processing Facility
PIMS Project Information Management System
PPE Personal Protective Equipment
Racking Process of disconnecting a circuit breaker from the bus
RMU Ring Main Unit
SCADA Supervisory Control and Data Acquisition
Short time
function Protection element of low voltage circuit breakers that has intentional delay
SLD Single Line Diagram
TCC Time-Current Curve
Total Clearing
Time Sum of the protection device operating time and the opening time of the circuit breaker
Upstream
protection
device
Feeder from the first upstream switchboard
V Voltage
WHS Workplace Health and Safety
Working
distance Distance between the worker and the potential arc source inside the equipment
50P Protection element of protection relays that has no intentional delay
51P Inverse-time overcurrent element of protection relays
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List of symbols
𝐶𝑓 Calculation factor
𝐷 distance from the possible arc point to person (mm)
𝐷𝐵 distance of the boundary from the arcing point (mm)
𝐸 is incident energy (J/cm2)
𝐸𝐵 incident energy at the boundary distance (J/cm2)
𝐸𝑛 normalized incident energy
𝐼𝑎 arcing current (kA)
𝐼𝑎,𝐿𝑉 arc current reflected in the LV side of the transformer (A)
𝐼𝑎/𝐻𝑉 arc current reflected in the HV side of the transformer (A)
𝐼𝑝𝑢 pickup setting of the protection relay (A)
𝐼𝑏𝑓 bolted fault current (kA)
𝑙𝑔 log10
𝑡 time (seconds)
𝑡𝑜 opening time of the circuit breaker (seconds)
𝑡𝑝 operating time of the protection device (seconds)
𝑡𝑡𝑜𝑡𝑎𝑙 total clearing time of the protection device (seconds)
𝑇𝐷 Time dial
𝑉 voltage (kV)
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1 Introduction
Aside from the risk of electric shock, the principal safety risk to electrical personnel operating and
maintaining high voltage (HV) and low voltage (LV) switchboards is exposure to arc flash from live
bare power terminals or conductors within switchboards. In the past decade, many industrial
companies across the globe have recognised the significance of understanding and mitigating the
hazards posed by arc flash events occurring in their facilities. While reported injuries caused by an
arc flash are rare, the cost related to these injuries can be very high, making them one of the most
important categories of injuries to avoid in an industrial workplace.
An arc flash will primarily occur when personnel are undertaking switching functions or
maintenance work that require switchboard doors to be opened or covers to be removed. In order to
quantify the amount of energy released during such an event, arc flash studies must be performed.
The purpose of this project is to determine the existing arc flash incident energy levels of HV and
LV switchboards installed in the Solomon Hub, which is owned by Fortescue Metals Group Limited
(“Fortescue”). The term “switchboard” will also include ring main units (RMUs) and motor control
centres (MCCs) for the rest of this document. The principal aims of the project are to reduce the
incident energy to less than 8 cal/cm2 where possible, and to determine the appropriate arc flash
personal protective equipment (PPE) where it is not feasible to reduce the incident energy to less
than 8 cal/cm2. To achieve these aims, the following tasks were conducted:
Verification of existing power network models and expanding the models where required;
Short circuit studies to determine maximum and minimum three-phase fault currents at the
switchboards;
Maximum and minimum arc current calculations;
Coordination studies to determine the clearing times of the protection devices for the
corresponding arc fault currents; and
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Incident energy and arc flash boundary calculations.
This thesis discusses how the study was conducted, the results of the studies based on the existing
state of the system, the proposed solutions as well as the arc flash studies results based on these
solutions. In addition, a section detailing different solutions that were investigated to mitigate the arc
flash hazard is included.
This report begins with a background section that will provide sufficient information about the
internship project and will give comprehensive facts in regards to the arc flash study.
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2 Background
2.1 Engineering Internship
Murdoch University engineering students must complete the unit ENG470-Engineering Honours
Thesis as one of the requirements for Bachelor of Engineering at Murdoch University. The internship
is one of two types of projects that engineering students at Murdoch University can undertake. The
internship placement provides students with exposure to their prospective industry while gaining
practical problem-solving experience. The aim of the unit is to develop the following graduate
attributes: communication, critical and creative thinking, social interaction, independent learning,
ethics and in-depth knowledge of the project topic.
The internship project took place at Fortescue’s corporate office in Perth under the direct supervision
of a senior Electrical Engineer. The placement was a full time position for 18 weeks where the main
task undertaken was the arc flash studies for the Solomon Hub. As part of the electrical engineering
team, the intern also undertook minor tasks such as power network modelling and simulations. These
tasks provided opportunities to turn theory learned from formal studies into practice, while gaining
invaluable skills and knowledge of how to become a successful engineer.
2.2 Fortescue Metals Group
Since the company’s inception in 2003, Fortescue Metals Group (FMG) has managed to acquire
several tenements in the Pilbara region of Western Australia where significant iron ore deposits have
been discovered. The company owns port facilities and a 620 km rail infrastructure that is used to
transport iron ore from the company’s two operating hubs, which include Cloudbreak, Christmas
Creek, Firetail and Kings Valley mines, as shown in Figure 1. The mining operation was built on an
existing mine lease and is now producing 165 million tonnes of iron ore per year, making Fortescue
the fourth largest iron ore producer in the world.
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Figure 1: Fortescue Metals Group Limited Operations Map [1]
2.2.1 Solomon Hub
Solomon Hub is located 120 km west of Chichester Hub and includes Firetail and Kings Valley
mines. Solomon Hub has almost twice the resource of Chichester Hub and produces more than 70
metric tonnes of iron ore per year [1]. The arc flash studies were conducted for switchboards installed
in the Solomon Hub, and hence this report will only focus on Solomon Hub’s electrical system.
2.2.1.1 Solomon Hub power system arrangement
Power for Solomon Hub is supplied by four 15MVA Solar Titan 130 (“MPU”) [2] and two GE
LM6000PF Dual Fuel Gas Turbine Generators with maximum individual capacity of 63.5MVA [3].
The power plant is owned by TransAlta and operated as an islanded electrical system. The plant
supplies power to the mining, crushing, screening, overland conveying, stock-piling and train load
out facilities, workshops, administration services buildings and an accommodation village.
Power from the LM6000 generators and MPUs is generated at 11kV. The MPUs are used to supply
power to the Primary Diesel Facility, Stockyard and RMU 10 at 11kV; while some of the generated
power is fed to Substation 1 for transmission at 132kV. Likewise, power from the LM6000
generators is stepped-up to 132kV by two transformers installed in Substation 1 for transmission.
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From Substation 1, power is transmitted to Substation 2 and Substation 3. In Substation 2, a 50MVA
transformer is used to step-down the voltage to 33kV and feed to a 33kV switchboard where
electricity is distributed to RMU 11, RMU 14 and Firetail ore processing facility (OPF) main 33kV
switchboard via two feeders. The power network set-up for Substation 3 is the same, although power
is distributed to RMU 29, RMU 12 and Kings Valley OPF.
The main 33kV switchboards in Firetail OPF and Kings Valley OPF have a number of outgoing
feeders that supply power to various plant switchrooms. From each switchroom, power is reticulated
to 6.6kV and 400V switchboards to provide power for motors and other electrical equipment
installed at the OPFs. The power network interconnection diagram for the Solomon Hub is shown in
Appendix A.
2.3 Project Background
Electricity is a widely used energy resource as it provides an efficient source of power for
applications such as lighting, heating and many others. Well maintained and operated electrical
equipment will offer a very high level of service and safety. One of the major pieces of electrical
equipment installed in an industrial facility is a switchboard. A switchboard is an assembly of panels
containing busbars, protection devices and auxiliary equipment that are critical to the safe and
continuous operation of electrical equipment. Electricity is transmitted to a switchboard from a
power supply, where it is distributed to downstream equipment. Shown in Figure 2 is a switchboard
installed in Substation 2 at the Solomon Hub that is used to distribute electricity to RMU 11, RMU
14 and Firetail OPF.
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Figure 2: Switchboard installed in Substation 2
A switchboard is the main point of isolation if downstream equipment is being tested or requires
maintenance and needs to be de-energised. However, electrical personnel working with, or in close
proximity to a switchboard must be aware that, under certain conditions, electrical switchboards
present a serious hazard. Industrial power networks operate at higher energy levels and higher
voltage levels than domestic systems and therefore an awareness of these additional hazards is
essential. When personnel are working on a switchboard, they are exposed not only to electric shock
but also to an arc flash hazard.
An arc flash hazard is a dangerous condition caused by an electric arc as a result of electrical faults
[4]. Because of the significant and even catastrophic nature of these events, elimination and
mitigation strategies continue to receive attention. An arc flash will primarily occur when personnel
are switching or racking a circuit breaker or maintenance work is being performed in the
switchboard. In order to determine the hazard posed by an arc flash event, arc flash studies must be
performed.
In August 2014, Fortescue’s Perth Engineering team initiated arc flash investigations as a critical
safety initiative. The goal of the overall study was to determine the arc flash hazard posed by
switchboards installed in the Solomon Hub and to find solutions to mitigate the hazard. The arc flash
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hazard assessment was limited to switchboards with voltage levels of at least 400V. Switchboards
that have a lower rating have a relatively low fault current associated with them, hence a low risk of
an arc fault developing with sufficient energy to cause a severe injury.
There is no regulatory requirement for the company to perform an arc flash study. However, to fulfil
the Workplace Health and Safety (WHS) requirement of the company, all measures must be
undertaken to ensure safety of personnel, and hence arc flash studies are recommended.
2.4 Arc flash
An arc flash is the release of heat and light energy when an insulator between energised conductors
fails and current flows through a normally nonconductive medium, such as air [5]. The arc flash
caused by dielectric breakdown is identical to the arc flash emitted by an arc welder. Some of the
causes of arc flash are:
Rats and snakes entering the equipment;
Using an item of under-rated measuring equipment;
Loose joints;
Tools left behind after maintenance; and
Tools accidentally touched two energised conductors.
When objects touch energised conductors, it can result in a short circuit fault. The large fault current
will result in a strong magnetic field, which in turn will propel the object away. As the object moves
away, the current continues to flow and forms very hot arcs which vaporise conductors and ionize
gases. An arc flash can also occur for the same reason when switching or racking a circuit breaker.
In systems with high voltage, tracking can also initiate an arc flash event. This occurs naturally due
to the dielectric breakdown value of air, making it possible for an arc flash to occur over a much
greater air gap, and also due to the tendency of partial discharge to occur over time across insulation,
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eventually leading to insulation breakdown and an arc fault developing. The arc formation in a
cubicle occurs across different phases [6]:
1. Compression phase: the air where the arc develops is overheated. Then, through
convection and radiation, the remaining volume of air inside the cubicle also increase in
temperature.
2. Expansion phase: as soon as the internal pressure increases, a hole in the cubicle is
formed where the superheated air begins to escape. The pressure increases until it
reaches its maximum value.
3. Emission phase: the superheated air is forced out by an almost constant overpressure
which is the result of the continued contribution of energy by the arc.
4. Thermal phase: after the discharge of air, the temperature inside the cubicle is close to
the arc’s temperature. The final phase lasts until the arc is extinguished, where the
materials inside the cubicle coming into contact, experience erosion with production of
gas, molten material and fumes.
The electric arc between metals is four times as hot as the surface of the sun, which is the hottest
temperature reached on earth [7]. In a bolted fault, such as phase-phase and phase-to-ground faults,
the fault current stays within the conductors where resistance is very low, therefore, little heat is
generated. For an arc fault, there is an appreciable resistance between conductors because a current
is flowing through the air. The heat generated is significant due to the higher resistance path between
conductors. The arc flash may blow equipment doors open and propel parts including molten metals.
The arc flash may continue until the generated voltage has been consumed or a protection device
clears the fault. The potential hazards caused by an arc flash event may include [8]:
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Burns – an electric arc produces heat energy where exposure experienced by personnel can
cause survivors to suffer debilitating and horrific burn trauma or death.
Projectiles hazard – arc faults result in rapid increase of pressure inside equipment causing
the ejection of loose items or metallic particles.
Intense light – an arc flash event emits high intensity light which can damage the eyes.
Sound waves – an arc flash event may cause permanent hearing loss due to sound generated
from the explosion.
Respiratory trauma – hazardous toxic gases are produced from molten metals or burnt
insulation which are harmful if inhaled.
2.5 Arc flash reported incidents and statistics
The potential for electrical injuries due to arc flash is a serious workplace health and safety problem.
The Department of Mines and Petroleum in Western Australia recorded four arc flash incidents from
2013 - 2015 that can be found in the Department’s Safety Publications Library [9]. All incidents
resulted in irreparable damage to equipment and, fortunately, only resulted in minor injuries to
personnel. The author of this report is aware that the number of arc flash incidents is many times
more than what was reported to the Department of Mines and Petroleum, although normally these
incidents are not reported to the relevant authority, and hence not viewable from public records. On
the 3rd of February 2015, two electricians died due to an arc flash event in a mall in Perth [10]. The
electricians were conducting routine maintenance on a switchboard when the incident happened. The
incident is still under investigation but it is believed that it was caused by human error. This event
highlights that even though arc flash events are uncommon compared to other electrical faults, they
can be very costly and even lethal.
In the USA, a report published by the NFPA states that electrical burns from arc flashes are the cause
of many work-related burns treated at burns centres [11]. Research conducted at a Texas burn centre
over a 20-year period found that 40% of burns were caused by electrical arc injuries and the length
of hospital stay for treatment was 11.3 days [11]. In addition, data from the Bureau of Labor Statistics
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shows that for a seven-year period starting in 1992, 2287 U.S. workers died and 32,807 workers
sustained lost time injuries because of electrical shock and burn injuries [12]. Of the 32,807 injuries,
38% were classified as electrical burns [12], which is the category that would include arc flash burns.
Furthermore, a research report by the National Institute for Occupational Safety and Health into arc
flash injuries in the mining industry noted that between 1990 and 2001, there were 836 arc flash
incidents on mine sites [13]. The majority of these incidents occurred during electrical work activities
including: installation (2%), maintenance (5%), repair and troubleshooting (42%), unspecified
electrical work (22%), during normal operation (19%) and unspecified cause (10%) [13]. Although
reported arc flash injuries are infrequent compared to other electrical injuries, the very high costs
associated with these injuries make them one of the most important categories of injuries in an
industrial workplace.
Extended hospitalisation and rehabilitation costs for personnel, coupled with litigation fees, fines,
investigation costs and increased insurance premiums, are often expensive. In addition, an arc flash
event can also cause irreparable damage to equipment which can lead to extensive downtime and
costly replacement and repair. The combined costs of the damage of one incident have been
estimated to potentially reach a total value of over USD 12 million [14]. As such, the potential
impacts highlight the importance of having mitigation strategies to reduce or eliminate arc flash
hazards.
2.5.1 Standards and WHS Requirements
Over the last decade, increasing attention has been placed on the arc flash hazards associated with
electrical switchboards. This has driven manufacturers to design and build safer switchboards that
specifically address arc flash risk. Electrical switchboards in Australia with a nominal supply current
of 800A or more shall be protected from arc faults while the equipment is in service or is undergoing
maintenance as per AS/NZS 3000:2007 [15].
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The Fortescue specification for LV switchboards 100-SP-EL-0001 is currently being revised and
will outline arc fault protection for LV switchboards that have nominal current of 400A and above,
which is in conformity with the enhanced PPE recommended for such switchboards as per AS/NZS
4836 [16] [17] [18]. For HV switchboards, the Fortescue specification 100-SP-EL-0016 states that
HV switchboards must have an arc fault containment rating, which is now becoming an industry
standard worldwide [19].
2.5.1.1 Internal Arc Fault Containment
Fortescue switchboards have Internal Arc Classification (IAC) certification, as specified in Section
8.3 and Annex A of AS/NZS 62271.200 – 2005, which is an adaptation of IEC 62271.200 modified
for Australian conditions. The arc fault containment is intended to offer a tested level of protection
in the event of internal arc fault for personnel in the vicinity of switchgear with rated voltage from
1kV up to and including 52kV [20]. Likewise, AS/NZS 3439.1:2002 provides guidelines for Internal
Arc Fault Containment testing with the intention of protecting personnel standing in front of an LV
switchboard from an internal arcing fault [21].
The IAC testing is subject to agreement between the switchboard manufacturer and the customer.
There are two types of test performed for IAC certification: the “special” test and the “standard” test.
The “special” test is conducted if additional security is required. For this test, arc faults are simulated
in different locations within a switchboard where it is possible for an arc fault to occur [22]. Due to
the additional cost of testing, when IAC certification is requested, the test that is normally conducted
is a “standard” test only. When conducting a “standard” test, the arc is initiated on the outgoing
terminal of the feeder, which is normally cleared instantaneously, and hence the arc flash energy is
reduced [22]. However, faults in other locations within a switchboard are possible. Nonetheless, the
probability of these faults is low, therefore IAC testing for faults at these locations is not generally
required [21]. Figure 3 shows locations within a switchboard where the initiation of an arc fault is
possible.
12
Figure 3: Locations within a switchboard where arc faults can occur: a) outgoing terminal of the feeder, b) feeder, c)
distribution bus, d) main busbar and e) incomer or incoming cable termination. (Redrawn from [23])
If the arc fault occurs at locations other than the outgoing terminal of the feeder, the first upstream
protection device will clear the arc fault. For example, if the fault is at the feeder or at the main
busbar, the first upstream protection device is the incomer. If the fault is at the incomer, the clearing
device is the feeder from the first upstream switchboard (upstream protection device), which is
normally located in another switchroom. Due to protection grading requirements, these protection
devices normally have longer operating times than the incomer protection device. As a result of
longer operating times, the arc flash energy is higher, and the switchboard arc fault containment
certified using the “standard” test might not be able to withstand the energy released under this
scenario.
Support from IAC test reports are needed before personnel can conduct normal operating duties
while the equipment is energised (with all panel doors closed) without requiring an arc flash PPE. In
order to verify that the whole switchboard is capable of withstanding internal arc faults, the test
13
report must specify that the test was conducted for all compartments within the switchboard, rather
than just on the outgoing terminal of the feeder.
The Fortescue’s records do not clearly show if switchboards installed in the Solomon Hub were IAC
certified using the “standard” test or the “special” test. It was known that all HV switchboards and
some LV switchboards have an IAC, however, without the certification to confirm this, personnel’s
safety could not be guaranteed when working on energised switchboards (with all panel doors
closed).
In addition, it is important to realise that even if the switchboards have been IAC tested, this can
only provide protection if covers and doors are closed and properly fixed in place. When the door or
cover of an arc resistant switchboard is open, the arc resistant properties of the equipment are
nullified. Hence, protection cannot be guaranteed if personnel are conducting normal operating
duties or maintenance work while doors are open. Hence, it is necessary that arc resistant
switchboards shall be included in the arc flash study.
2.6 Arc Flash Studies
An arc flash study is used to quantify the arc flash hazard by calculating the arc flash energy. An arc
flash study is considered a continuation of short-circuit and coordination studies because the results
of each of these studies are required for the arc flash hazard analysis. The arc flash hazard assessment
is used to identify and implement controls to reduce the likelihood and severity of an arc flash
accident. After conducting an arc flash assessment, the calculated energy will determine the required
PPE for personnel working on or near electrical equipment. In addition, the result of the assessment
can be used to establish the limits of approach to energised electrical equipment, identify hazard
management, and identify mitigation actions. When performing an arc flash hazard assessment, a
good knowledge of the electrical network in a facility and the electrical protection system is required.
14
Globally, two North American standards have dominated arc flash hazard assessment [24]: The
NFPA 70E, Standard for Electrical Safety in the Workplace; and the IEEE Std 1584-2002, IEEE
Guide for Performing Arc Flash Hazard Calculations. Prior to the Australian Standard, ENA NENS
09 – 2014 [25] for arc hazard quantification coming into place in 2014, and even currently, the USA
standards IEEE 1584 and NFPA 70E were widely adopted by the Australian Engineering
Community.
2.6.1 NFPA 70E
The National Fire Protection Association (NFPA) 70E standard [26] provides guidelines for
electrical safety in the workplace and selection of arc flash PPE. NFPA 70E is a safety standard that
describes work practices that can help protect electrical personnel from electrical hazards including
electrocution, electric shock, arc blast and arc flash. Section 130 of the NFPA 70E provides task and
equipment based tables that can be used in determining arc flash PPE requirements, hence known as
the “table” method. These tables give pre-defined levels of PPE based on the tasks that are to be
performed, the magnitude of the fault current and the associated clearing time of the protection
device. The “table” method takes a three-step approach:
1. Conduct a risk assessment to determine if the condition of the equipment and the task
that is to be performed warrants the used of arc flash PPE. If PPE is not required, no
further action is necessary, otherwise, proceed to step 2.
2. Determine the working distance and calculate the magnitude of the prospective fault
current and the associated clearing time of the protection device.
3. Determine the arc flash PPE category requirement for the task specified in step 1.
The arc flash energy depends on complex relationships between system voltage, bolted and arcing
fault current, arc impedance, clearing time of protection devices, conductor spacing, confinement in
an enclosure, and system grounding [27]. Some of these variables are not considered in the selection
of arc flash PPE based on the “table” method outlined in the NFPA 70E standard. For this reason,
15
the “table” method is of limited practical use and this could explain why there is a general preference
for using the other method outlined in the IEEE Std 1584 - 2002.
2.6.2 IEEE Std 1584 – 2002
The IEEE Std 1584 – 2002: IEEE Guide for Performing Arc-Flash Hazard Calculations, outlines the
methodology, including providing relevant equations, to determine the arc flash boundary and the
incident energy to which employees could be exposed during their work on or near electrical
equipment [28]. The arc flash boundary is the distance from the arc source where personnel are
exposed to 1.2 cal/cm2 of energy that can lead to a second degree burn [29]. Personnel not wearing
arc flash PPE must not go within the arc flash boundary to avoid exposure to high levels of arc flash
energy. The incident energy is the amount of energy that can reach a person’s face or torso standing
at a specific distance relative to the origin of the arc [30]. The incident energy calculation is not
based on exposure on the hands or arms which will be closer to the arc source if conducting energised
work, because injury to these areas is less life threatening. The equations within the IEEE 1584
standard was developed from statistical analyses using data from a large number of laboratory tests
conducted by the IEEE 1584 working group. Table 2 shows the parameter range for electrical
systems where the empirically derived equations are valid [30]. For equipment with voltage levels
above 15kV, equations based on a theoretical model developed by Ralph Lee [7], which are included
in the IEEE 1584 standard, can be applied.
Table 2: Limitations of equations from IEEE 1584
Parameter Applicable Range
System voltage 0.208kV – 15kV
Frequency 50/60 Hz
Bolted fault current 0.7kA – 106kA
Gap between electrodes 13 – 152 mm
Equipment enclosure type Open air, box, MCC, panel, switchgear and cables
Grounding type All types of grounding and ungrounded
Faults Three phase
The IEEE 1584 standard does not consider the risk of an arc flash occurring nor the effect of arc
fault containment. Instead, the standard is limited to the hazard posed by thermal energy, and the
effects of molten metals, projectiles and toxic by-products are not considered. Nonetheless, industrial
16
companies still have an obligation to complete Arc Flash Hazard assessment to mitigate arc flash
hazards. IEEE 1584 is based on the most comprehensive laboratory experiments and calculations
available; therefore, where arc flash hazard quantification is needed, the IEEE 1584 is generally
used.
2.7 Assumptions and Clarifications
The random nature of arcs makes them very difficult to model precisely. The equations in
the IEEE 1584 standard that are used for the analyses are developed based on average values.
Parameters used are selected to achieve what are considered to be the worst case results.
Calculations are based on three-phase faults.
The inrush currents of transformers are assumed to equal 12 times the transformer rating.
The inrush current of DOL motors are assumed to equal 6 times the motor rating.
Other assumptions are stated in the relevant sections where these assumptions are implemented.
2.8 PowerFactory
The software that was used for all the simulations is DIgSILENT PowerFactory. PowerFactory is an
engineering tool used for the analysis of electrical transmission and distribution systems. The
software was developed by programmers and engineers with extensive experience in computer
programming and electrical systems analysis [31]. The equations used and the results of the
simulations have been confirmed in a large number of implementations of power systems throughout
the world.
17
3 Methodology
3.1 System audit, data collection and power system modelling
A system audit was conducted to determine the state of the power network electrical model. During
the system audit, the network model was compared to the latest single line diagrams (SLDs). The
model was found to require a significant amount of work to bring it to a state where it would
accurately represent the complete Solomon Hub power network. It was found that many equipment
parameters used in the PowerFactory model were incorrect. In order to provide accurate incident
energy calculations, the network model needs to be as accurate as possible. Some parameters, like
the cable impedances, can have a significant effect on the fault levels. However, it was found that
many cables were not modelled, and some had incorrect lengths entered, which resulted in incorrect
impedance values. Moreover, some transformers were modelled using typical impedance values
instead of actual nameplate impedance values. Whilst impedance values may differ only slightly, a
small variation of available fault current may significantly affect the calculated magnitude of the
incident energy for a switchboard [32]. As a result, it was necessary to obtain accurate and complete
data pertaining to the cable and transformer specifications. Those data were then used to update the
PowerFactory model. This task identified an unexpected number of existing errors, and therefore
was time-consuming, taking approximately one month of full time investigation by the intern.
Another problem encountered during the project was that many electrical loads and switchboards
that are included in the present arc flash study had not previously been modelled into the simulation
software. Hence, the respective SLDs for these types of equipment were obtained and used to update
the model in the simulation software. The switchboards were modelled using “busbar” blocks while
all the loads were modelled using “general load” blocks in the PowerFactory software. There are
numerous electrical loads connected at each switchboard, however, they were modelled as a single
load. This is because modelling each load separately will give no additional information about the
power network compared with modelling a single composite load [33]. The power ratings of the
loads were taken from the Solomon electrical load list 224632-SL-2000-LL-EL-0002 [34] and the
18
load factors were assumed to equal 100% of the rated capacity. The load factor will not affect the
fault simulations; but in load flow simulations, it will result in maximum current demand, which is
considered to be the worst-case scenario.
Finally, it was found that all LV circuit breakers were not modelled into the simulation software and
the protection settings were not available. The protection devices need to be modelled in the software
so that a Time-Current Curve (TCC) can be generated, which will be used to determine the operating
time of these devices when a fault is simulated. As a result, the intern travelled to Solomon hub to
obtain the settings of the LV circuit breakers, which can be found in Appendix B. Most of the
protection settings were collected except for the settings of a few protection devices that were not
accessible or were not operational during the visit. Consequently, site personnel at Solomon Hub
were requested to gather the remaining protection settings after they became operational.
One more methodological problem encountered in the project is that, unfortunately, even though
most of the required protection settings were obtained, the LV circuit breakers cannot be modelled
into PowerFactory software because Fortescue did not have this included in the PowerFactory
protection devices library. As a result, all the operating times calculations for all LV circuit breakers
were performed manually.
3.2 Short-Circuit Study
Short-circuit simulations were conducted to determine the fault levels at each switchboard. It was
assumed that any unbalanced arc fault will immediately escalate to three-phase faults because air is
ionized around the conductors [30]. Hence, only faults involving three phases were simulated. The
fault currents that flow as a result of three-phase short-circuit faults at each switchboard were
determined using the “complete” method. With this method, fault currents are determined by
superimposing a healthy load-flow condition before the fault initiation, resulting in more realistic
and more accurate fault calculations [31].
19
Unlike in protection studies where the maximum fault current is assumed to provide worst-case
conditions, for an arc flash study, the worst-case short-circuit current assumptions do not always
produce the most severe arc flash incident energy results, as will be explained in the next section.
For simple radial systems similar to the Solomon hub’s electrical network, IEEE 1584 suggested that
two sets of calculations are required [30]. The first calculation is for the minimum short-circuit
current conditions and the second is for maximum short-circuit current conditions.
Both the maximum and minimum short-circuit conditions should be evaluated to determine the effect
on the protective device clearing times and the incident energy exposures. The variations between
the results of these two calculations can have a significant effect on the accuracy of the evaluations
for the arc flash hazard and the PPE requirements for each switchboard. There are different operating
modes that can significantly change the fault levels at the switchboards, which were identified. The
first operating mode was the basis of the maximum short-circuit calculations and included motor
contributions, while the second and third operating modes were the basis of the minimum short-
circuit calculations and excluded motor contributions. The operating modes were:
1. One LM6000 generator and all MPUs are in service (126MVA of generation) for maximum
fault simulations.
2. One LM6000 generator and one MPU are in service (79MVA of generation) for Stockyard
and RMU10 minimum fault simulations.
3. Three MPUs are in service (47MVA of generation) for minimum fault simulations for the
OPFs.
3.2.1 Effect of motor contributions in the calculations
Another variable that can affect the fault levels are current contributions from induction motors.
When a fault occurs, induction motors momentarily contribute current to the fault. The Solomon
Hub’s electrical system includes many induction motors, although around half of the major induction
20
motors are driven by variable speed drives (VSDs). A VSD effectively separates the motors from
the rest of the system, and hence a VSD-driven motor does not contribute to the fault current. The
fault contribution from a single motor is not significant, however, the individual contributions adds
up, which can result in a significant increase in the fault level. Unlike the contribution from the
generators, contributions from motors decay rapidly and may not be present for the whole duration
of an arc flash event [35].
Neither IEEE 1584 nor NFPA 70E provides guidance on how to calculate motor contributions,
however, PowerFactory can calculate motor contributions and include them in fault simulations. For
minimum fault simulations, it was assumed that there are no contributions from the motors, whereas,
for the maximum fault simulations, PowerFactory was set to include contributions from motors, to
obtain the highest fault current magnitude. When calculating the clearing time of protection devices
manually (as was the case for the LV circuit breakers), it is important that contributions from motors
downstream of the faulted bus are excluded because these currents are not passing through the
incoming and upstream protection devices that are used to interrupt the fault current.
To illustrate this, Figure 4 shows a PowerFactory fault simulation analysis where a fault was
introduced in Switchboard 2. It can be seen that Motor M2 is located downstream of Switchboard 2
and contributed 5kA to the fault. The rest of the network, including other motors, supplied a total of
31.835kA of current to the fault. Motor M2’s contribution does not flow through the incomer and
the upstream protection device. Consequently, this can have a significant effect on the incident
energy calculation because it will affect the clearing time of the protection devices. The importance
of using a correct value for the fault magnitude in clearing time calculations is further explained in
Sections 3.3 and 3.4.
21
Figure 4: Fault simulation showing motor contributions
3.3 Arc current calculations
The bolted fault currents found in the short-circuit study were used to calculate the arcing current
using either equation (1) or equation (2), depending on the voltage level.
For switchboards with a voltage under 1000V [29, p.10]:
𝐼𝑎 = 10K+0.662(𝑙𝑔𝐼𝑏𝑓)+0.0966V+0.000526G+0.5588V(𝑙𝑔𝐼𝑏𝑓)−0.00304G(𝑙𝑔𝐼𝑏𝑓) (1)
For switchboards with a voltage of 1000V or higher [29, p.10]:
𝐼𝑎 = 100.00402+0.983(𝑙𝑔𝐼𝑏𝑓) (2)
where
𝐼𝑎 is the arcing current (kA)
K is a constant which has a value of -.097
𝑙𝑔 is the log10 function
𝐼𝑏𝑓 is the bolted fault current (kA)
G is the gap between conductors seen in Table 3 (mm)
V is the system voltage (kV)
22
Table 3: Distance factors and typical conductor gaps used for the arc flash calculations [30]
Voltage (kV) Typical conductor gaps x (distance factor)
0.208 - 1 32 1.473
>1 - 5 13-102 0.973
>5 - 15 153 0.973
The minimum arc current values were further reduced by 15% as recommended in Section 9.10.4 of
IEEE 1584. This was done because it is very difficult to accurately predict the arcing current and a
small change in current could result in a significant change in clearing time. To illustrate this, the
time current curve (TCC) of a protection relay protecting a 33kV switchboard is shown in Figure 5.
Notice the change in relay clearing time when transitioning from the “definite-time” region of the
TCC to the “inverse” region of the TCC. As illustrated in Figure 5, when the arc fault current is
reduced by 10%, the clearing time is increased from 0.02 s to 0.5 s, which resulted in a significant
increase in incident energy.
Figure 5: TCC illustrating the significant increase in incident energy for a 10% arc current reduction
23
3.4 Coordination studies
The objective of coordination studies is to ensure that protection devices are properly designed and
coordinated [36]. Coordination studies are used to determine the operating time of protection devices
and to ensure that these devices will detect faults and isolate the faulted part of the system without
compromising reliability. Conventionally, coordination studies were targeted at reliability, with all
protection settings adjusted towards clearing bolted faults. However, as there are new arc flash safety
requirements, this means that from now on all coordination studies (including the present study) used
to determine the appropriate settings for the protection devices must not only clear bolted faults but
they must also clear arc faults.
The operating times of protection devices were determined based on the minimum and maximum
arc current values calculated using the equations presented in Section 3.3. The accuracy of the
operating time is important because this is the most dominant factor influencing incident energy [37].
For each switchboard, out of two calculations, the arc fault current magnitude that resulted in
protection device operating time that led to worst-case scenario was used. For switchboards that are
protected by a fuse, the minimum arcing fault currents are the basis of the worst-case calculations
for the incident energy [38]. For switchboards that are protected by circuit breakers or protection
relays, the worst-case calculations vary according to the regions of the TCC. If the arc fault current
magnitude falls completely within any region of the TCC where the time remains constant, the
maximum arc fault current will result in the calculation of the worst-case incident energy. However,
if the arc fault current falls within the “inverse” region of the TCC, depending on the steepness of
the curve, the lower arcing fault values can sometimes result in the worst-case scenario calculations,
because it will correspond to longer clearing times (illustrated in Figure 6). Incident energy is a
function of several parameters including the arc current and the clearing time of the protection
device, where a lower fault current can sometimes be counteracted by an associated increase in fault
clearing time, thereby leading to higher incident energy. Therefore, in order to determine the worst-
case incident energy for instances when the arc current value falls within the “inverse” region of the
24
TCC, two calculations were conducted. The first calculation used the maximum arc current value
and the associated clearing time of the protection device while the second calculation used the
minimum arc current value and the associated clearing time of the protection device.
Figure 6: TCC illustrating the effect of the clearing characteristics of a protection relay on the incident energy
Note that the opening times of the circuit breakers were added to the operating time of protection
devices. The opening time has a value range of 0.03 s – 0.06 s depending on the type and model of
the circuit breaker.
3.5 Incident energy and arc flash boundary calculations
After the coordination study, arc flash boundary and incident energy calculations were performed
using equations from IEEE 1584. Incident energy is the amount of energy that can reach a person’s
face or torso if an arc flash occurs. The incident energy was calculated using equation 3 and equation
4 for switchboards that have a voltage of less than 15kV [29, p.11].
25
𝐸𝑛 = 10𝐾1 + 𝐾2 + 1.081𝑙𝑔𝑙𝑎 +0.0022G (3)
where
𝐸𝑛 is the incident energy (J/cm2) normalised for time and distance
𝐾1 is a constant that has a value of -0.555 for switchboard incident energy calculations
𝐾2 is a constant that has a value of -0.113 if the system is solidly grounded, otherwise it has a
value of 0
𝐸 = 4.184𝐶𝑓𝐸𝑛 (𝑡
0.2) (
610𝑥
𝐷𝑥 ) (4)
where
𝐸 is the incident energy (J/cm2)
𝐶𝑓 is a calculation factor that has a value of 1.5 for a switchboard that has a voltage level of
1kV and below, otherwise, it has a value of 1
𝑡 is arcing time (seconds)
𝐷 is a person’s distance relative to the origin of the arc (mm)
𝑥 is a distance exponent from Table 3
For switchboards where the voltage level is 15kV or above, the theoretically derived equation by
Ralph Lee was used [29, p.12]:
𝐸 = 2.142 𝑥 106𝑉𝐼𝑏𝑓(𝑡
𝐷2) (5)
The possible working distances for the switchboards were determined from the equipment manuals
by inspecting the switchboard dimensions. However, these distances will vary depending on the task
that is being performed. To cater for worst-case scenario, the working distance for the LV
switchboards was assumed to be equal to 610 mm while the working distance for HV switchboards
was assumed to be equal to 910 mm. The assumptions were based on the advice of the supervising
electrical engineer at Fortescue who has a good knowledge of switchboard construction.
26
In addition, the arc flash boundary, which is the distance from the arc source at which a person can
receive a second degree burn, was calculated. Any person crossing the arc flash boundary is required
to wear the appropriate arc flash PPE. If the switchboard has a voltage of less than 15kV, equation 6
is used; otherwise, equation 7 is used [29, p.12].
𝐷𝐵 = [4.184𝐶𝑓𝐸𝑛 (𝑡
0.2) (
610𝑥
𝐸𝐵)]
1
𝑥 (6)
𝐷𝐵 = √2.142𝑥106𝑉𝐼𝑏𝑓 (𝑡
𝐸𝐵) (7)
where 𝐷𝐵 is the incident energy (J/cm2) and x the distance exponent from Table 3.
3.6 PPE selection
The required PPE if personnel are exposed to arc hazards is shown in Table 4. The PPE category
was chosen based on the magnitude of the incident energy which was calculated in the previous step.
This is the minimum level of PPE recommended from NFPA 70E standard with the intent to protect
personnel from the thermal effects of the arc flash at working distance.
Table 4: PPE requirements based on incident energy exposure [26]
Min Incident
Energy (cal/cm2)
Max Incident Energy
(cal/cm2) PPE Category
Required PPE Rating
(cal/cm2)
0 1.2 0
1.21 4 1 4
4.1 8 2 8
8.1 25 3 25
25.1 40 4 40
40.1 And above X Specialised PPE
required
27
3.7 Process flowchart
The arc flash studies performed for this project were made up of several tasks that were explained in
the previous sections. The aim of the studies is not just to quantify the arc flash hazards and
recommend PPE, but also to find solutions to mitigate the hazard. Figure 7 shows the process flow
chart illustrating the steps conducted to achieve the goals of the arc flash studies.
Figure 7: Flow chart which illustrate the steps conducted to achieve the goals of the arc flash studies
28
4 Results
Switchboards were evaluated to determine if either the incomer or the upstream protection device
should be used for the calculation of the incident energy. In this study, it was assumed that an arc
fault can occur at the load side of the incomer or at the incomer itself. An incoming protection device
can only detect faults at its load side, which is normally in a separate compartment. If this happens,
the incomer will clear the fault, and hence its operating time will be used for the incident energy
calculations. If the fault is at the incoming protection device itself, then the upstream protection
device will provide the protection. The identification of the correct protection device is very
important because the clearing times will vary, depending on which device trips. The arc flash studies
results were categorised based on the location of the fault within switchboards.
4.1 Stockyard
The summary of the arc flash study results for switchboards installed in the Stockyard area is shown
in Table 5. The complete arc flash study results for the Stockyard area can be found in Appendix C.
These results are based on the existing settings of the protection devices. As previously mentioned,
two incident energy calculations were conducted for each switchboard: one is when the fault is at
the load side of the incomer (a “switchboard”) and another is when the fault is at the incomer itself
where the upstream protection device will clear the fault. An arc fault at the incomer can occur when
personnel are switching or racking the incoming protection device. It can be seen that some
switchboards have very high arc flash incident energy that is well above the desired limit of 8
cal/cm2.
Table 5: Arc flash study results for switchboards installed at the Stockyard
Equipment Clearing Device
Location
Maximum
Arc Current (kA)
0.85 x
Minimum
Arc Current (kA)
Total
Clearing Time (s)
Incident
Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash
Boundary (mm)
0.4kV Incomer
Upstream 8.03-13.89 6.81-11.58 0.75- 2.28 14.66-55.72 3336-8259
0.4kV Switchboards
Incomer 8.03-13.89 6.81-11.58 0.06-0.43 1.00-12.92 538-3061
11kV
Incomer Upstream 5.37-18.49 3.75-9.21 0.42-0.67 3.59-8.40 2809-6725
11kV Switchboards
Incomer/Upstream 5.37-18.49 3.75-9.21 0.08-0.67 1.58-21.82 1204-17934
29
The incomers possess the greatest arc flash hazard, with SUB-801-SWB01 incomer CB and
SUB901-MCC01 incomer CB having 54.93 cal/cm2 and 55.72 cal/cm2 potential incident energy,
respectively (see Appendix C). These energy levels are higher than the withstand rating of PPE’s
available at the Stockyard area and, therefore, a mitigation strategy must be implemented as soon as
possible.
4.2 Firetail
The results of the arc flash study for switchboards installed at Firetail OPF are summarised in Table
6. The complete arc flash study results for the Stockyard area can be found in Appendix D. It can
be seen that all 6.6kV switchboards have a calculated incident energy of less than 8 cal/cm2, which
is the ideal result. However, people working in 0.4kV and 33kV switchboards are exposed to very
high arc flash incident energy. For the 0.4kV switchboards, it can be seen that the highest potential
incident energy exposure is 43.82 cal/cm2 if an arc fault occurs at SR102-MCC01 incomer. In
addition, it can be seen that the incident energy of 33kV switchboards are well above the desired
limit of 8 cal/cm2.
Table 6: Arc flash study results for switchboards installed at Firetail OPF
Moreover, Table 6 shows that the feeder from Substation 2 will clear faults in all 33kV switchboards.
The incomer and the upstream protection devices for the 33kV switchboards will detect the fault but
the feeder from Substation 2 will operate first. The protection devices do not have the correct
coordination, and hence a three-phase fault in any of the 33kV switchboards installed at Firetail OPF
Equipment
Clearing
Device
Location
Maximum
Arc Current
(kA)
0.85 x Minimum
Arc Current
(kA)
Total
Clearing
Time (s)
Incident
Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash
Boundary
(mm)
0.4kV Incomer Upstream 16.38-18.04 13.24-13.28 1.07-1.10 38.43-43.82 6418-7016
0.4kV
Switchboards Incomer 16.38-18.04 13.24-13.28 1.25 37.62-41.77 6326-6791
6.6kV Incomer Upstream 3.90-5.26 2.93-3.02 0.66-0.67 4.04-5.55 3166-4390
6.6kV
Switchboards Incomer 3.90-5.26 2.93-3.02 0.41-0.42 2.54-4.93 1967-3888
33kV Incomer
/Switchboards
Substation 2
Feeder to
Firetail OPF
4.52-4.59 2.06-2.10 0.39-0.41 35.41-37.58 4944-5086
30
has the potential to result in unnecessary power outages in Firetail OPF. The latter problem will be
considered when recommending the proposed solutions.
4.3 Kings Valley
The results of the arc flash studies for switchboards installed in Kings Valley OPF is summarised in
Table 7. The complete arc flash study results for Kings Valley OPF can be found in Appendix E.
The incident energy of 6.6kV switchboards remain below the desired limit of 8 cal/cm2. However,
the 0.4kV switchboards remain a serious risk, many 0.4kV switchboards have an incident energy
greater than 40 cal/cm2 where there is no available PPE to protect personnel. As such, energised
maintenance work at these switchboards should not be allowed unless steps to mitigate the risk are
taken. This is especially the case for switchboards 2500-SR509-MCC02 where the potential incident
energy is 92.27 cal/cm2.
A further finding is that the incident energy of all 33kV switchboards are below the maximum
incident energy limit of 8 cal/cm2. However, the 33kV protection system has no fault grading from
Substation 3 feeders. Substation 3 feeders to Kings Valley OPF will trip instantaneously for a fault
in any of the 33kV switchboards installed at Kings Valley OPF, including faults at the HV terminal
of the transformers. As a consequence, power will be unnecessarily taken out at the Kings Valley
OPF if a three-phase fault occurs in the 33kV system. This problem will be considered when
recommending the proposed solutions.
Table 7: Arc flash study results for switchboards installed at Kings Valley OPF
Equipment
Clearing
Device Location
Maximum
Arc Current (kA)
0.85 x
Minimum Arc Current
(kA)
Total
Clearing Time (s)
Incident
Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash
Boundary (mm)
0.4kV Incomer Upstream 14.98-18.39 12.30-13.40 1.06-1.17 38.11-45.14 6382-7159
0.4kV Switchboards
Incomer 14.98-18.39 12.30-13.40 0.45-3.00 13.17-92.27 3102-11631
6.6kV Incomer Upstream 3.96-5.36 3.00-3.02 0.66 4.07-5.66 3195-4480
6.6kV
Switchboards Incomer 3.96-5.36 3.00-3.02 0.42-0.84 2.57-6.67 1990-5302
33kV Incomer CBs/Switchboards
Substation 3
Feeder to Kings
Valley OPF
4.68-4.86 2.01-2.05 0.08 7.64-7.87 2296-2330
31
4.4 RMUs + other attached switchboards
The results of the arc flash study for the RMUs and other switchboards that are fed from the RMUs
are summarised in Table 8. The complete arc flash studies result for these switchboards can be found
in Appendix F. The 0.4kV switchboards’ arc flash incident energy levels are dangerously high. In
particular, the SR701-MCC01 switchboard has a calculated incident energy of 116.54 cal/cm2 and
there is no commercially available PPE that can withstand this energy exposure. Hence, energised
work on this switchboard should not be allowed until mitigating steps have been taken.
The calculated incident energy for the 6.6kV switchboards remain below 8 cal/cm2. This is also the
case for most tasks on the 0.69kV switchboard. However, it is not the case when personnel are
switching or racking the 0.69kV switchboard incomers where personnel are exposed to high incident
energy levels reaching 52.08 cal/cm2 for the CV763-VSD02 switchboard incomer. Moreover, it can
be seen that the arc flash incident energy of the 33kV switchboards are below 8 cal/cm2, which is
desirable. However, these results are based on the existing settings of the protection devices which
do not have correct coordination. The protection settings of these devices will be adjusted to ensure
the reliability of the protection system. However, as a consequence of changing these settings, the
arc flash incident energy at these switchboards will increase. The proposed protection settings to
ensure selectivity and for reduced arc flash incident energy are discussed in Section 7 of this report.
Table 8: Arc flash study results for RMUs and loads fed from the RMUs
Equipment
Clearing
Device Location
Maximum
Arc Current (kA)
0.85 x
Minimum Arc Current
(kA)
Total
Clearing Time (s)
Incident
Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash
Boundary (mm)
0.4kV Incomer Upstream 7.26-19.04 6.12-15.33 0.60-4.45 15.94-94.42 3531-11815
0.4kV Switchboards
Incomer 7.26-19.04 6.12-15.33 0.09-6.5 3.13-116.54 1168-13629
0.69kV Incomer Upstream 15.05-21.20 12.50-17.04 0.84-1.11 29.01-52.08 5303-7888
0.69kV
Switchboards Incomer 15.05-21.20 12.50-17.04 0.09 2.95-4.27 1123-1444
6.6kV Incomer Upstream 3.39-3.53 2.15-2.25 0.77-0.92 4.21-4.79 3304-3775
6.6kV
Switchboards Incomer 3.39-3.53 2.15-2.25 0.52 2.71-2.83 2100-2198
33kV Incomer
/Switchboards
Substations
1 and 2 4.36-4.86 2.01-2.09 0.08 7.11-7.93 2216-2340
32
5 Discussion
From the results of the arc flash studies, it is evident that many switchboards have unacceptably high
incident energy values that need to be improved. Contrary to what was believed by many electrical
personnel, the arc flash hazard posed by LV switchboards has been found to actually be more
significant than the arc flash hazard posed by HV switchboards. This is due to the higher available
fault current for LV systems. When the voltage is stepped down by a transformer, the current is
increased. Electrical personnel interact with LV switchboards more often than HV switchboards.
Therefore, statistically, the risk of having an arc flash incident in LV switchboards is actually higher.
In addition, normally, coordination studies are performed to select the appropriate settings of
protection devices to clear bolted faults. However, for LV systems, the magnitude of the arc current
is much lower than the bolted fault current and therefore, a protection device might take longer to
clear the arc fault or maybe it will not detect it at all. To illustrate this further, a numerical calculation
is shown below to calculate the incident energy of switchboard 2500-SR509-MCC02 installed at
Kings Valley, using the arc current values that were found to result in the worst-case incident energy.
Figure 8 shows the single line diagram that depicts the fault and shows the clearing devices.
Figure 8: Fault simulation showing the faulted switchboard
33
For the protection of the incomer protection device, the maximum arc current of 16.71kA was used
because it would result in worst-case incident energy:
𝐼𝑎/𝐻𝑉 = 16710 𝑥 0.417
33= 211𝐴 (7)
Where 𝐼𝑎/𝐻𝑉 is the arc current referred to the HV side of the transformer. Using the protection
settings of the upstream protection device, the operating time of the upstream protection device was
calculated using Equation 8 [38, p.108]. The protection device’s 50P element with pickup setting of
700A would not detect the arc fault current of 211 A, hence, the 51P element was used in order to
calculate the result for the hypothetical worst-case incident energy level. The protection device has
a time dial (TD) setting of 0.21, pickup setting of 50 A and the curve type was set to C1.
𝑡𝑝 = 𝑇𝐷 (0.14
(𝐼𝑎/𝐻𝑉
𝐼𝑝𝑢)
0.02
−1
) (8)
𝑡𝑝 = 0.21 (0.14
(211
50)
0.02−1
) = 1.01 𝑠
𝑡𝑡𝑜𝑡𝑎𝑙 = 𝑡𝑝 + 𝑡𝑜 (9)
𝑡𝑡𝑜𝑡𝑎𝑙 = 1.01 + 0.05 = 1.06 𝑠
where
TD is the time dial setting of the protection relay
𝐼𝑝𝑢 is the pickup setting of the protection relay
𝑡𝑝 is the operating time of the protection device
𝑡𝑜 opening time of the circuit breaker
𝑡𝑡𝑜𝑡𝑎𝑙 is the total clearing time of the protection device
Then, using equation 3 and 4, the incident energy was calculated to be equal to 38.86 𝑐𝑎𝑙
𝑐𝑚2.
34
For the protection of the remaining sections of the switchboard, the incomer, which is an LV circuit
breaker, would clear the fault. Hence, the incomer’s operating time was used for the calculation
which can be found in Appendix B. The minimum arc current of 13.25kA was used in order to
calculate the result for the hypothetical worst-case incident energy level. The protection device’s
short-time and instantaneous time elements have pickup settings of 21.6kA and 26.4kA respectively
which are above the arc current of 13.25kA. Hence, these elements will not detect the fault and
therefore, the long-time element was used for the incident energy calculations. The protection device
has a pickup setting of 2400 and the curve type was set to C-04. The total clearing time of the device
can be approximated from the curve shown in Appendix G, but first, it must be scaled [39]:
𝑆𝑐𝑎𝑙𝑖𝑛𝑔 = 𝐼𝑎,𝐿𝑉
𝐼𝑝𝑢 (10)
𝑆𝑐𝑎𝑙𝑖𝑛𝑔 = 13250
2400= 5.5
Where 𝐼𝑎,𝐿𝑉 is the arc current in the LV side of the transformer. Approximating from the curve, 5.5
equates to 3 seconds total clearing time as seen from the curve in Appendix G. Then, using equation
3 and 4, the incident energy was calculated to be equal to 92.27 𝑐𝑎𝑙
𝑐𝑚2.
When considering the results of the above calculations, it is evident that the arc flash incident energy
levels are very high. This is because the protection devices were set without consideration for arc
faults. The value of the arc current is a lot lower compared to the bolted fault current in LV systems.
And in this instance, the magnitude of the arc fault falls within the “inverse” region of the TCCs of
the devices, which in turn has led to longer operating times and higher incident energy.
On the other hand, all 6.6kV switchboards were found to have very low arc flash incident energy
levels with potential incident energy exposure not exceeding 8 cal/cm2. Therefore, the existing PPEs
that are currently used in Solomon Hub which are rated at 12 cal/cm2 are appropriate for continued
usage.
35
In addition, the 0.69kV switchboards were found to have low arc flash incident energy levels with
potential incident exposure not exceeding 8 cal/cm2, except when the arc fault occurs at the incomer
where personnel are exposed to incident energy of up to 52.08 cal/cm2, and therefore energised work
should not be conducted until mitigating procedures have taken place.
Currently, most of the 33kV switchboards have manageable arc hazard levels with arc flash incident
energy having been found to be less than 8 cal/cm2. An exception was the 33kV switchboards
installed at Firetail where the incident energy levels were found to be 23.37 cal/cm2 – 37.58 cal/cm2.
Although the arc flash hazard levels for switchboards other than those installed at Firetail were at
safe levels, the 33kV system has no grading from protection devices installed at Substation 2 and
Substation 3. A three-phase fault anywhere in the 33kV system will result in unnecessary power
outage to other healthy equipment. For example, if there is a fault at the HV terminal of a transformer
in Kings Valley OPF, the protection device installed at Substation 3 will clear the fault which will
result in unnecessary power outages to other equipment operating at Kings Valley. It will be
recommended that the protection settings of these devices be adjusted to ensure the reliability of the
protection system. However, as a consequence of changing these settings, the arc flash incident
energy levels at these switchboards will increase. This is a major problem that needs to be resolved
and this will be considered when recommending solutions for the arc flash studies.
It would seem then that using arc flash studies solely as a means to determine the required PPE
requirements is not the most effective control method for minimizing potential danger to personnel.
Engineers must conduct risk assessments and identify possible risk mitigation strategies by
identifying which controls are feasible for mitigation of arc flash hazards. A hierarchy of controls is
a system used in the industry to help prevent or reduce hazards [40]. Numerous safety organizations
have promoted this method and it is widely accepted in the industry. As depicted by the triangle in
Figure 9, the methods considered to be least effective are at the bottom whilst the methods considered
the most effective are at the top:
36
Figure 9: Hierarchy of controls (redrawn from [40])
A preferred approach is to use solutions higher in the pyramid, that is, elimination, substitution and
engineering; although these alternatives are not always feasible. The different controls to reduce the
arc flash hazard were investigated.
5.1 Elimination
Elimination is the most ideal control method to protect personnel from arc flash hazards. The
elimination of arc flash hazards can be achieved if electrical work is performed only while equipment
is not energised. However, it is not feasible to switch off equipment every time testing or
maintenance functions are performed. This is especially true for the switchboards installed at the
Solomon Hub as the cost of a few hours of de-energised work can result in millions of dollars of lost
revenues. Furthermore, if equipment de-energisation was to become the chosen option, it involves
circuit breaker switching, racking and isolation verification which would also have associated arc
flash hazards that would need to be controlled.
5.2 Substitution
Substituting equipment like switchboards and protection devices for faster arc fault clearing is
impractical. The cost associated with the procurement and installation of this type of equipment
makes this control method infeasible. As a result, this control method was not considered.
37
5.3 Engineering Controls
5.3.1 Optimise protection settings
It has been determined from engineering research that the arc time has a linear effect in the incident
energy [30], whereby reducing the protection device’s clearing time proportionately reduces arc flash
incident energy. Therefore, the most effective solution to mitigate the arc flash hazard is to reduce
the operating time of the protection devices to clear arc faults as rapidly as possible. Protection
settings must be chosen to ensure high levels of protection for equipment while still allowing normal
operating currents and inrush currents to flow without causing equipment to trip. In addition, grading
between protection devices must not be compromised, and therefore the protection device closest to
the fault must be the only one that trips so that service will only be interrupted to a minimal portion
of the power network. Proper coordination between protection devices will result in protection
devices closer to the power source having longer clearing times and higher pickup levels compared
to protection devices further downstream. This means that protection devices downstream can clear
faults faster than the upstream protection devices, thereby avoiding an unnecessary power outage to
a larger portion of the power network. Consequently, optimising protection settings may not always
be a feasible solution for arc flash mitigation due to protection grading requirements.
5.3.2 Installing a maintenance switch
An alternative and simple method for the reduction of incident energy is to install a maintenance
switch. A maintenance switch is an external switch that is wired into a protection device to allow
personnel to activate maintenance mode protection settings. A maintenance mode protection setting
is a pre-set setting which allows fast clearing of arc faults (in most cases, instantaneously) [41].
For protection relays, the 50P element is activated, and for LV circuit breakers, the instantaneous
element is used. Both elements are used to detect faults without unintentional delay. If the
maintenance mode is activated, the grading between the protection devices will be compromised.
However, the maintenance switch will only be engaged when personnel are working on a
switchboard, and it must be deactivated as soon as switching/maintenance work at the switchboard
38
is completed. Switching to maintenance mode can be included in permit conditions to ensure it is a
mandatory step.
5.3.3 Zone Selective Interlocking Scheme
The Zone Selective Interlocking (ZSI) scheme is a method recognised in the engineering field used
to speed up the operating time of protection devices without sacrificing protection devices
coordination and introducing nuisance tripping into the system [42]. This concept allows protection
devices to communicate across the distribution zones. The information is transmitted from the
feeders to the incomers through wires or using communication infrastructure like supervisory control
and data acquisition (SCADA).
The concept of ZSI is best explained in a visual format, as shown in Figure 10. If a fault occurs
downstream of feeder F3, where the magnitude of the fault exceeds the pick-up settings of both
feeder F3 and the incomer, both protection devices will detect the fault. However, feeder F3 will
send a restraint signal to the incomer which will activate the pre-set time delay for the incomer’s
operating time allowing feeder F3 to clear the fault. The ZSI scheme allows the incomer to clear the
fault with little intentional delay. The incomer cannot be set to trip instantaneously because it needs
to allow the feeder to send the restraint signal where there is an inherent time delay. However, the
incomer time delay can still be set for a faster operating time because the incomer does not need to
grade with downstream protection devices. As a result, proper coordination and selectivity is
maintained while still providing back-up protection for feeder F3.
39
Figure 10: Zone selective interlocking
5.3.4 Remote Operation
Increasing the working distance between the possible origin of an arc flash and the personnel is also
an effective method to reduce exposure to an arc flash hazard. Therefore, another known effective
method to mitigate the arc flash hazard when switching or racking the circuit breakers is to perform
these tasks remotely. The remote operation of the circuit breakers can be achieved by installing a
remote switching and racking panel outside the arc flash boundary or using the SCADA
infrastructure where personnel can operate the equipment in front of a human machine interface
(HMI) panel or a personal computer (PC).
40
5.4 Administrative control
There are administrative controls that are already employed to mitigate arc flash hazards when
working at energised switchboards at the Solomon Hub. These include risk assessments, safety
related working procedures and safety training. Arc flash labels are currently not available, however
Fortescue intends to implement these based on the arc flash study results that were calculated in the
present project. This method of labelling equipment showing the level of arc flash hazard exposure
and the appropriate PPE will assist personnel in making informed choices about how to safely
perform their work.
5.5 PPE
There are PPE clothing options rated at 12 cal/cm2 and 40 cal/cm2 available at Solomon electrical
rooms. However, the use of PPE must be the last line of defence applied and all other means must
be investigated to reduce the arc flash hazard to an acceptable level. PPE clothing options with higher
category ratings are known to be heavy and uncomfortable, and capable of restricting vision and
movement. These drawbacks can make it difficult to complete many tasks, which means that this
protection equipment is also creating a hazard. The requirement set by FMG is the reduction of arc
flash incident energy to not greater than 8 cal/cm2 if feasible, so that the lighter PPEs rated at 12
cal/cm2 available at Solomon Hub can be used.
41
6 Recommendations
From Section 5, it can be seen that numerous arc flash hazard mitigation strategies exist. The
challenge is to find the optimal strategy that can be implemented on an existing facility like the
Solomon Hub. Implementing many of these strategies are difficult for engineers due to excessive
capitals costs and retrofitting costs that limit their feasibility. Incorporating the findings of the present
project, and following thorough research of the engineering literature and discussions with senior
engineers, it was decided that Fortescue would implement three engineering controls at the Solomon
Hub mines: protection settings optimisation, installing maintenance switches and remote operation.
Based on the results of the arc flash hazard studies, optimising the 50P element of protection relays
and the instantaneous protection settings of LV circuit breakers appeared to be the superior option
due to the very low costs associated with this strategy. Therefore, the settings of all LV incomers
and some HV incomers were optimised so that arc faults can be cleared fast, thereby reducing
incident energy exposure. These protection settings will give consideration to the inrush current from
motors and transformers during the energisation stage. Hence, the proposed protection settings will
clear arc faults fast, reducing the incident energy significantly while maintaining protection system
reliability. However, this method is not always feasible due to protection grading requirements, and
hence it can only be applied to some protection devices.
Where grading requirements do not allow for the mitigation of the arc flash hazard by optimising
protection settings, installing maintenance switches is proposed. Switching to maintenance mode
when working on the switchboard will be included in permit conditions to ensure it is a mandatory
step. A physical switch will be wired to the protection device, which will be used to activate the
maintenance mode protection settings. Initially, it was proposed to install 52 maintenance switches.
The majority were to be installed on the upstream protection devices, which are normally located in
another switch room. It was also noted that the existing SCADA infrastructure has the capability of
also being used to remotely activate the maintenance mode settings from upstream protection
42
devices. However, further investigation needs to be conducted to determine the feasibility of using
SCADA to activate the settings.
Arc flash calculations were performed based on the proposed optimised protection settings and
maintenance mode protection settings for the 52 protection devices. It was found that the potential
incident energy exposure from all switchboards would be reduced to less than 8 cal/cm2, which is a
significant improvement on the existing incident energy exposures. However, the number of
maintenance switches that would need to be installed is not practical due to the high cost of
installation and due to large distances, varying from a few hundred metres to just over 1 km, that
would limit accessibility. Ultimately, it was decided to use remote operation to mitigate the arc flash
hazard when switching or racking the LV incomers, which resulted in the reduction in the number
of maintenance switches that needed to be installed to just three, (the settings and locations can be
found in Appendix H). A remote switching and racking panel would be installed inside the
switchroom where the incomers are located. The switches that would be used to remotely switch or
rack the incomers would be wired to the protection devices. This method could eliminate the arc
flash hazard because the remote switching and racking panel would be installed outside the arc flash
boundary, and hence personnels’ safety could be assured.
The proposed optimised protection settings and the results of the arc flash studies based on these
settings can be found in Appendices, I, J, K and L. The findings regarding the proposed solutions of
optimising protection settings, installing maintenance switches and utilising remote operation, if
implemented, will meet the principal aim of this project, which was to reduce the incident energy to
less than 8 cal/cm2. As a result, by applying the three solutions in the appropriate situations, the
existing PPEs rated at 12 cal/cm2 can be used for energised work in the switchboards installed at the
Solomon Hub mines.
43
Finally, it was found that the 33kV system does not have correct protection grading for three-phase
faults. While it is not part of the project, it is a major problem that need to be resolved. Therefore,
protection settings to resolve this problem were proposed which can be found in Appendix M. The
proposed protection settings will ensure the reliability of the protection system while giving
consideration to clearing time for arc flash.
44
7 Conclusion
The main purpose of this project is to conduct arc flash studies for switchboards installed at
Fortescue’s Solomon Hub. The aim of the studies is to find feasible solutions to reduce arc flash
incident energies to less than 8 cal/cm2 and to provide appropriate arc flash PPE recommendations.
The arc flash studies were conducted based on IEEE 1584-2002 Standard, the IEEE Guide for
Performing Arc-Flash Hazard Calculations. PowerFactory was used to perform short-circuit analyses
and coordination studies and the results were used to provide the information that is required for the
completion of an arc flash hazard analyses for each switchboard.
The arc flash study results summarised in Section 4 indicate that the existing arc flash incident energy
of some switchboards installed at the Solomon Hub are significantly above the desired level of 8
cal/cm2. Contrary to what was believed at the start of the studies, the LV switchboards represent the
most significant hazards, where many have incident energy greater than 40 cal/cm2, which is above
the withstand rating of PPEs available at Solomon Hub. In addition, it was found that the potential
incident energies of 0.69kV switchboards will depend on the task that is being performed. Switching
or racking the incomer create a significant arc flash hazard with many have incident energies greater
than 8 cal/cm2. Other switchboards that have voltages of 6.6kV and 11kV have low potential incident
energies except for SUB801-SWB01 switchboard, which has a potential incident energy of 21.82
cal/cm2.
Moreover, the 33kV switchboards have manageable arc flash hazards (with arc flash incident
energies less than 8 cal/cm2), with the exception of the 33kV switchboards installed at Firetail OPF,
where the incident energy levels are 23.37 cal/cm2 – 37.58 cal/cm2. However, the 33kV protection
system has no protection grading, if the correct protection settings are implemented, the incident
energies will increase.
45
While the main objective of this project was to conduct arc flash studies for switchboards installed
in the Solomon Hub, insufficient protection grading was found in a number of areas. As a result, the
recommendations for this project also included protection setting changes to ensure the reliability
and selectivity of the protection system. The main grading problems (for three-phase faults) that
were found were:
The 33kV system at Firetail has no three-phase fault grading. Faults in any of the 33kV
switchboards installed at Firetail will take out the whole Firetail OPF.
The 33kV system at KV has no three-phase fault grading. Fault in any of the 33kV
switchboards installed at KV will take out the whole KV OPF.
The feeders from RMUs have no three-phase fault grading with upstream protection
devices at Substation 2 and Substation 3.
The recommended solutions to reduce the arc flash hazard and to resolve the grading problems are
discussed in Section 6. To mitigate the arc flash hazard, three simple solutions were proposed:
1. Optimise protection settings
2. Maintenance switches
3. Remote operation
The proposed engineering controls will significantly reduce the arc flash incident energy for all
switchboards to less than 8 cal/cm2 which is the principal aim of this project. As a result, the existing
PPEs rated at 12 cal/cm2 can be used for energised work in the switchboards installed at the Solomon
Hub mines without compromising personnel safety. These results represent a significant
achievement and the project is considered to have been a resounding success.
46
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metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and
including 52 kV, Sydney: Standards Australia, 2005.
[21] Standards Australia, AS/NZS 3439.1:2002 - Low-voltage switchgear and controlgear, Sydney:
Standards Australia, 2002.
[22] D. Stonebridge, ARC FAULT PROTECTION STANDARDS FOR HEAVY CURRENT LV
SWITCHGEAR, Perth: Industrial Electrix, 2015.
[23] D. Stonebridge, ARC FAULT PROTECTION IN LV SWITCHGEAR, Perth: Industrial Electrix, 2014.
[24] M. Steyn and G. Nagel, “Arc Flash Hazard Reduction by Fault Clearance Acceleration,” in Arc
Flash & Isolation Safety Conference, Perth, 2015.
[25] Energy Networks Association, ENA NENS 09 -2014: National Guideline for the Selection, Use
and Maintenance of Personal Protective Equipment for Electrical Arc Hazards, Sydney:
Standards Australia , 2014.
[26] National Fire Protection Association, NFPA 70E - Standard for Electrical Safety in the
Workplace, Quincy: National Fire Protection Association, 2015.
[27] G. T. Homce and J. Cawley, “Understanding and Quantifying Arc Flash Hazards in the Mining
Industry,” IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, vol. 47, no. 6, pp. 2437-2444,
2011.
[28] K. Lippert, D. Colaberardino and C. Kimblin, “UNDERSTANDING ARC FLASH HAZARDS,” in
Pulp and Paper Industry Technical Conference, Appleton, 2004.
[29] X. Liang, B. Bagen and D. W. Gao, “An Effective Approach to Reducing Arc Flash Hazards in
Power Systems,” in IEEE Industry Applications Society Annual Meeting, Vancouver, 2014.
[30] Institute of Electrical and Electronics Engineers, IEEE Guide for Performing Arc-Flash Hazard
Calculations, New York: Institute of Electrical and Electronics Engineers, 2002.
48
[31] DigSILENT GmbH, PowerFactory 15 User Manual, Gomaringen: DigSILENT GmbH, 2014.
[32] W. Tinsley and M. Hodder, “A Practical Approach to Arc Flash Hazard Analysis and
Reduction,” in IEEE IAS Pulp and Paper Industry Conference, Victoria, 2004.
[33] International Electrotechnical Commision, IEC 60909-0:2001 - Short-circuit currents in three-
phase a.c. systems - Part 0: Calculation of Currents, Geneva: International Electrotechnical
Commision, 2001.
[34] Aurecon, FMG T155 Solomon Project Ore Processing Facilities, Perth: Fortescue Metals
Group Ltd., 2012.
[35] W. Tinsley, M. Hodder and A. Graham, “ARC FLASH HAZARD CALCULATIONS: MYTHS, FACTS
AND SOLUTIONS,” in IEEE IAS Pulp and Paper Industry Technical Conference, Appleton,
2006.
[36] M. Holt, “What is Arc Flash?,” Mike Holt Enterprises, Inc., 2004. [Online]. Available:
https://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/What-is-Arc-
Flash~20040512.php. [Accessed 11 January 2016].
[37] P. Willis, “Arc Flash Standards - Australian Developments,” in Electrical Arc Flash Forum ,
Melbourne, 2010.
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Moon Township: Eaton Corporation, 2006.
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GE Consumer & Industrial GmbH, 2010.
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Environmental & Safety Professionals, 2009. [Online]. Available:
http://www.environet.com.au/services.asp?id=20&cid=16. [Accessed 14 01 2016].
[41] N. Thompson, Arc Faults - Safety Measures and Detection, Auckland: NHP, 2013.
[42] C. G. Walker, “Arc flash energy reduction techniques zone selective interlocking & energy-
reducing maintenance switching,” in Pulp and Paper Industry Technical Conference (PPIC),
Nashville, 2011.
49
9 Appendices
9.1 Appendix A – Solomon Interconnection diagram
50
9.2 Appendix B – LV incomers Settings
It is important to inspect the relevant manuals to understand the interpretation of values in the
following tables.
Table 9: Existing Stockyard .4 kV MCC protection settings
Table 10: Existing Firetail .4 kV MCC protection settings
Existing Stockyard .4 kV MCC protection settings
Location Descriptor Protection device I rating In(xICT) LT PU LTD (s) ST PU trip time (s) INS PU
SUB801 SUB801
Incomer Terasaki 2500 1 0.9 10 3 0.4 16
SUB801 SK802
Incomer Terasaki 1250 0.63 0.8 20 8 0.2 10
SUB801 RC901
Incomer Terasaki 800 0.5 0.8 2.5 6 0.2 12
SUB901 SUB901
Incomer Terasaki 2500 1 0.9 10 3 0.4 6
Existing Firetail .4 kV MCC protection settings
Location Descriptor Protection
device
I
rating Ir LT PU
LT
Band
ST
PU
ST
Band
Inst
PU
SR203 Firetail SR203 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
SR104 Firetail SR104 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
SR102 Firetail SR102 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
SR502 Firetail SR502 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
SR402 Firetail SR402 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
SR303 Firetail SR303-MCC02 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
SR303 Firetail SR303-MCC01 Incomer GE
MPD32W32 3200 2400
0.75 x
rating C2
6 x
Ir 5
10 x
rating
51
Table 11: Existing KV .4 kV MCC protection settings
Table 12: 0.4kV MCCs fed from RMUs
Existing KV .4 kV MCC protection settings
Location Descriptor Protection
device
I
rating Ir LT PU
LT
Band
ST
PU
ST
Band Inst PU
SR303 Kings Valley SR303-MCC03 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR303 Kings Valley SR303-MCC02 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR303 Kings Valley SR303-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR104 Kings Valley SR104-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
2 x
rating
SR102 Kings Valley SR102-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR203 Kings Valley SR203-MCC02 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR203 Kings Valley SR203-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR702 Kings Valley SR702-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR402Kings Valley SR402-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
SR509 Kings Valley SR509-MCC03 incomer GE
MPD32W32 3200 2400
0.75 x
rating C4
9 x
Ir 10
2 x
rating
SR509 Kings Valley SR509-MCC02 incomer GE
MPD32W32 3200 2400
0.75 x
rating C4
9 x
Ir 10
11 x
rating
SR505 Kings Valley SR505-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
2 x
rating
SR503 Kings Valley SR503-MCC01 incomer GE
MPD32W32 3200 2400
0.75 x
rating
C
MIN
9 x
Ir 10
10 x
rating
0.4kV MCCs fed from RMUs
Location Descriptor Protection device I
rating In(xICT)
LT
PU
LTD
(s) ST PU
trip time
(s)
INS
PU
SR706 SR706-MCC01
INCOMER Terasaki 1250 0.8 1 10 6 0.4 16
SR705 SR705-MCC01
INCOMER Terasaki 1600 1 0.8 10 1 0.4 off
SR703 SR703-MCC01
INCOMER Terasaki 1250 0.8 1 10 6 0.4 16
SR701 SR701-MCC01
INCOMER Terasaki 1600 1 1 10 6 0.4 16
SR707 SR707-MCC01
INCOMER Terasaki 1600 1 0.85 10 1 0.4 2
52
Table 13: Exising incomer protection settings for VSDs
Protection
device In LT PU (x In) t ST Inst PU (x In)
CV763-VSD02 incomer ABB 1600 0.975 3
no ST
protection
4
CV125-VSD01 incomer ABB 1600 1.025 3 4
CV704-VSD03 incomer ABB 2500 1 144 4
CV704-VSD02 incomer ABB 2500 1 144 4
CV704-VSD01 incomer ABB 2500 1 144 4
CV705-VSD03 incomer ABB 2500 1 144 4
CV153-VSD01 incomer ABB 1600 1 144 4
CV123-VSD01 incomer ABB 2500 1 144 4
CV113-VSD01 incomer ABB 2500 1 144 4
CV763-VSD01 incomer ABB 1600 0.9 3 4
CV705-VSD01 incomer ABB 1600 1 3 4
CV705-VSD02 incomer ABB 1600 0.95 3 4
53
9.3 Appendix C – Arc flash study results for the Stockyard
Table 14: Arc flash study results for 0.4kV switchboards installed at the Stockyard based on the existing protection settings
Equipment
Clearing
Device
Location
Maximum
Bolted Fault
Current (kA)
Maximum
Arc
Current
(kA)
Minimum
Bolted Fault
Current
(kA)
0.85 x
Minimum
Arc Current
(kA)
Total
Clearing
Time (s)
Working
Distance
(mm)
Incident
Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash
Boundary
(mm)
PPE
SUB801-SWB01 Incomer
Upstream 30.54 13.89 29.80 11.58 2.18 610 53.78 8062 X
SUB801-SWB01
Switchboard Incomer 30.54 13.89 29.80 11.58 0.43 610 12.92 3061 3
SK801-MCC01 Incomer
Upstream 28.42 13.12 27.07 10.73 0.91 610 20.67 4213 3
SK801-MCC01
Switchboard Incomer(1) 28.42 13.12 27.07 10.73 610
SK802-MCC01 Incomer
Upstream 22.74 10.98 21.94 9.08 0.75 610 14.22 3268 3
SK802-MCC01
Switchboard Incomer 22.74 10.98 21.94 9.08 0.06 610 1.40 677 1
RC901-MCC01 Incomer
Upstream 15.35 8.03 15.31 6.81 1.15 610 15.98 3537 3
RC901-MCC01
Switchboard Incomer 15.35 8.03 15.31 6.81 0.06 610 1.00 538 0
SUB901-MCC01 Incomer
Upstream 29.48 13.51 28.61 11.21 2.28 610 54.30 8116 X
SUB901-MCC01
Switchboard Incomer 29.48 13.51 28.61 11.21 0.43 610 12.53 2999 3
(1) Protection settings not available.
Table 15: Arc flash study results for 11kV switchboards installed at the Stockyard based on the existing protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
CV801-VSD01 Switchboard Upstream 19.04 18.28 11.09 9.13 0.08 910 2.57 1993 1
CV801-VSD02 Switchboard
Upstream 19.15 18.38 11.14 9.17 0.08 910 2.59 2005 1
CV802-VSD01 Switchboard
Upstream 19.16 18.39 11.14 9.17 0.08 910 2.59 2007 1
CV902-VSD01 Switchboard
Upstream 12.09 11.70 7.87 6.52 0.08 910 1.59 1214 1
CV902-VSD02 Switchboard
Upstream 12.07 11.68 7.87 6.52 0.08 910 1.58 1204 1
CV902-VSD03 Switchboard
Upstream 12.13 11.73 7.87 6.52 0.08 910 1.59 1218 1
CV902-VSD04 Switchboard
Upstream 12.10 11.71 7.87 6.52 0.08 910 1.59 1215 1
CV901-VSD01 Switchboard
Upstream 12.08 11.69 7.87 6.52 0.08 910 1.59 1213 1
CV901-VSD02 Switchboard
Upstream 12.10 11.71 7.87 6.52 0.08 910 1.59 1215 1
CV901-VSD03 Switchboard
Upstream 12.11 11.71 7.87 6.52 0.08 910 1.59 1216 1
SUB901-SWB01 Switchboard
Upstream 12.18 11.78 7.92 6.56 0.42 910 8.40 6725 3
SUB901-SWB01 Incomer CB
Incomer 12.18 11.78 7.92 6.56 0.37 910 7.40 5903 2
SUB801-SWB01 Switchboard
Upstream 19.26 18.49 11.18 9.21 0.67 910 21.82 17934 3
SUB801-SWB01 Incomer
Incomer 19.26 18.49 11.18 9.21 0.67 910 21.82 17934 3
RC901-SWB01 Switchboard
Upstream 5.48 5.37 4.48 3.75 0.42 910 3.59 2809 1
RC901-SWB01 Incomer
Incomer 5.48 5.37 4.48 3.75 0.40 910 3.42 2672 1
54
9.4 Appendix D – Arc flash study results for Firetail OPF
Table 16: Arc flash study results for 0.4kV switchboards installed at Firetail OPF based on the existing protection settings
Table 17: Arc flash study results for 6.6kV switchboards installed at Firetail OPF based on the existing protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
2200-SR201-MCC02 Incomer
Upstream(1) 4.03 3.97 3.56 2.99 910
2200-SR201-MCC02 Switchboard
Incomer 4.03 3.97 3.56 2.99 0.41 910 2.54 1967 1
2200-SR201-MCC01 Incomer
Upstream(1) 4.05 3.99 3.59 3.02 910
2200-SR201-MCC01 Switchboard
Incomer 4.05 3.99 3.59 3.02 0.41 910 2.55 1977 1
SR103-MCC01 Incomer
Upstream 4.01 3.96 3.55 2.98 0.66 910 4.07 3195 2
SR103-MCC01 Switchboard
Incomer 4.01 3.96 3.55 2.98 0.42 910 2.57 1992 1
SR101-MCC01 Incomer
Upstream 4.02 3.97 3.56 2.99 0.66 910 4.08 3204 2
SR101-MCC01 Switchboard
Incomer 4.02 3.97 3.56 2.99 0.42 910 2.58 1998 1
SR501-MCC01 Incomer
Upstream 4.02 3.97 3.55 2.98 0.66 910 4.08 3198 2
SR501-MCC01 Switchboard
Incomer 4.02 3.97 3.55 2.98 0.42 910 2.58 1997 1
SR401-MCC01 Incomer
Upstream 3.96 3.90 3.49 2.93 0.67 910 4.04 3166 2
SR401-MCC01 Switchboard
Incomer 3.96 3.90 3.49 2.93 0.42 910 2.55 1971 1
SR301-MCC01 Incomer
Upstream 5.36 5.26 3.55 2.98 0.66 910 5.55 4390 2
SR301-MCC01 Switchboard
Incomer 5.36 5.26 3.55 2.98 0.59 910 4.93 3888 2
SR301-MCC02 Incomer
Upstream 4.39 4.33 3.55 2.98 0.66 910 4.48 3527 2
SR301-MCC02 Switchboard
Incomer 4.39 4.33 3.55 2.98 0.42 910 2.83 2199 1
(1) Protection settings not available.
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc Current (kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
SR203-MCC01 Incomer
Upstream 37.59 16.39 35.38 13.28 1.07 610 38.43 6418 4
SR203-MCC01 Switchboard
Incomer 37.59 16.39 35.38 13.28 1.25 610 35.76 6330 4
SR104-MCC01 Incomer
Upstream 37.54 16.38 35.27 13.24 1.1 610 39.46 6535 4
SR104-MCC01 Switchboard
Incomer 37.54 16.38 35.27 13.24 1.25 610 35.64 6326 4
SR102-MCC01 Incomer
Upstream 42.39 18.04 35.34 13.27 1.1 610 43.82 7016 x
SR102-MCC01 Switchboard
Incomer 42.39 18.04 35.34 13.27 1.25 610 35.73 6791 X
SR502-MCC01 Incomer
Upstream 39.80 17.16 35.34 13.27 1.1 610 41.5 6762 X
SR502-MCC01 Switchboard
Incomer 39.80 17.16 35.34 13.27 1.25 610 35.73 6545 4
SR402-MCC01 Incomer
Upstream 40.93 17.54 35.37 13.28 1.09 610 42.13 6831 X
SR402-MCC01 Switchboard
Incomer 40.93 17.54 35.37 13.28 1.25 610 37.47 6653 4
SR303-MCC02 Incomer
Upstream 38.95 16.86 35.32 13.26 1.1 610 40.73 6677 X
SR303-MCC02 Switchboard
Incomer 38.95 16.86 35.32 13.26 1.25 610 35.70 6463 4
SR303-MCC01 Incomer
Upstream 41.07 17.59 35.33 13.26 1.1 610 42.64 6887 X
SR303-MCC01 Switchboard
Incomer 41.07 17.59 35.33 13.26 1.25 610 40.65 6667 X
55
Table 18: Arc flash study results for 33kV switchboards installed at Firetail OPF based on the existing protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
2200-SR201-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.57 4.57 2.47 2.10 0.39 910 36.32 5006 4
2100-SR103-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.45 4.45 2.42 2.06 0.39 910 35.41 4944 4
2100-SR101-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.53 4.53 2.45 2.08 0.39 910 36.02 4986 4
2550-SR501-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.54 4.54 2.45 2.08 0.41 910 37.58 5092 4
2400-SR401-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.56 4.56 2.46 2.09 0.41 910 37.58 5092 4
2300-SR301-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.52 4.52 2.44 2.07 0.41 910 37.48 5086 4
2000-SR001-SWB01 Switchboard/Incomer
SUB002 Feeder to
Firetail 4.59 4.59 2.47 2.10 0.39 910 36.43 5014 4
56
9.5 Appendix E – Arc flash study results for Kings Valley OPF
Table 19: Arc flash study results for 0.4kV switchboards installed at KV OPF based on the existing protection settings
(1) Protection settings not available.
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
2300-SR303-MCC03 Incomer
Upstream 36.34 15.96 34.88 13.12 1.12 610 39.07 6490 4
2300-SR303-MCC03 Switchboard
Incomer 36.34 15.96 34.88 13.12 0.45 610 13.17 3102 3
2300-SR303-MCC02 Incomer
Upstream 39.57 17.08 35.23 13.23 1.11 610 41.67 6780 X
2300-SR303-MCC02 Switchboard
Incomer 39.57 17.08 35.23 13.23 0.45 610 13.17 3260 3
2300-SR303-MCC01 Incomer
Upstream 38.92 16.85 32.10 12.29 1.17 610 43.3 6959 X
2300-SR303-MCC01 Switchboard
Incomer 38.92 16.85 32.10 12.29 0.45 610 13.97 3229 3
2100-SR104-MCC01 Incomer
Upstream 36.81 16.12 35.22 13.23 1.11 610 39.15 6500 4
2100-SR104-MCC01 Switchboard
Incomer 36.81 16.12 35.22 13.23 0.45 610 13.17 3260 3
2100-SR102-MCC01 Incomer
Upstream 43.42 18.39 35.26 13.24 1.11 610 45.14 7159 X
2100-SR102-MCC01 Switchboard
Incomer 43.42 18.39 35.26 13.24 0.45 610 13.17 3260 3
2200-SR203-MCC02 Incomer
Upstream 39.19 16.95 35.05 13.18 1.11 610 41.33 6743 X
2200-SR203-MCC02 Switchboard
Incomer 39.19 16.95 35.05 13.18 0.45 610 14.05 3242 3
2200-SR203-MCC01 Incomer
Upstream 40.49 17.39 34.49 13.01 1.12 610 42.88 6914 X
2200-SR203-MCC01 Switchboard
Incomer 40.49 17.39 34.49 13.01 0.45 610 14.45 3304 3
2700-SR702-MCC01 Incomer
Upstream 37.37 16.32 35.78 13.40 1.10 610 39.31 6517 4
2700-SR702-MCC01 Switchboard
Incomer 37.37 16.32 35.78 13.40 0.45 610 13.49 3153 3
2400-SR402-MCC01 Incomer
Upstream 39.91 17.19 34.81 13.11 1.12 610 42.35 6856 X
2400-SR402-MCC01 Switchboard
Incomer 39.91 17.19 34.81 13.11 0.45 610 14.27 3276 3
2500-SR509-MCC03 Incomer
Upstream 33.56 14.98 32.13 12.30 1.17 610 38.11 6382 4
2500-SR509-MCC03 Switchboard
Incomer 33.56 14.98 32.13 12.30 2.5 610 91.66 11579 X
2500-SR509-MCC02 Incomer
Upstream 38.50 16.71 35.28 13.25 1.06 610 38.86 6467 4
2500-SR509-MCC02 Switchboard
Incomer 38.50 16.71 35.28 13.25 3 610 92.27 11631 X
2500-SR509-MCC01 Incomer
Upstream 37.94 16.51 35.26 13.24 1.11 610 40.18 6615 X
2500-SR509-MCC01 Switchboard
Incomer(1) 37.94 16.51 35.26 13.24 610
2570-SR505-MCC01 Incomer
Upstream 37.18 16.25 35.16 13.21 1.11 610 39.5 6538 4
2570-SR505-MCC01 Switchboard
Incomer 37.18 16.25 35.16 13.21 0.45 610 13.43 3144 3
2550-SR503-MCC01 Incomer
Upstream 39.40 17.02 35.31 13.26 1.11 610 41.52 6763 X
2550-SR503-MCC01 Switchboard
Incomer 39.40 17.02 35.31 13.26 0.45 610 14.12 3252 3
57
Table 20: Arc flash study results for the 6.6kV switchboards installed at KV OPF based on the existing protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
2300-SR302-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.08 3197 2
2300-SR302-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1993 1
2300-SR301-MCC02
Incomer Upstream 5.46 5.36 3.57 3.00 0.66 910 5.66 4480 2
2300-SR301-MCC02
Switchboard Incomer 5.46 5.36 3.57 3.00 0.42 910 3.58 2795 1
2300-SR301-MCC01
Incomer Upstream 5.10 5.01 3.57 3.00 0.66 910 5.26 4158 2
2300-SR301-MCC01
Switchboard Incomer 5.10 5.01 3.57 3.00 0.84 910 6.67 5302 2
2100-SR103-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.07 3196 2
2100-SR103-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1993 1
2100-SR101-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.08 3199 2
2100-SR101-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1994 1
2200-SR201-MCC03
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.07 3193 2
2200-SR201-MCC03
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1988 1
2200-SR201-MCC02
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.08 3198 2
2200-SR201-MCC02
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1994 1
2200-SR201-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.08 3200 2
2200-SR201-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.58 1995 1
2700-SR701-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.07 3195 2
2700-SR701-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1992 1
2400-SR401-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.07 3193 2
2400-SR401-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1990 1
2500-SR508-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.08 3199 2
2500-SR508-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.57 1994 1
2570-SR504-MCC02
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.08 3200 2
2570-SR504-MCC02
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.58 1998 1
2570-SR504-MCC01
Incomer Upstream 4.02 3.96 3.57 3.00 0.66 910 4.07 3197 2
2570-SR504-MCC01
Switchboard Incomer 4.02 3.96 3.57 3.00 0.42 910 2.58 1996 1
2550-SR501-MCC02
Incomer Upstream 4.02 3.98 3.59 3.02 0.66 910 4.09 3207 2
2550-SR501-MCC02
Switchboard Incomer 4.02 3.98 3.59 3.02 0.42 910 2.58 2002 1
58
(1) Protection settings not available.
Table 21: Arc flash study results for 33kV switchboards installed at KV OPF based on the existing protection settings
2550-SR501-MCC01
Incomer Upstream 4.02 3.97 3.59 3.02 0.66 910 4.08 3199 2
2550-SR501-MCC01
Switchboard Incomer(1) 4.02 3.97 3.59 3.02 910
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
2300-SR301-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.75 4.75 2.37 2.01 0.08 910 7.74 2312 2
2100-SR103-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.72 4.72 2.37 2.01 0.08 910 7.70 2305 2
2100-SR101-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.73 4.73 2.38 2.02 0.08 910 7.72 2308 2
2200-SR201-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.75 4.75 2.38 2.02 0.08 910 7.75 2312 2
2700-SR701-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.68 4.68 2.36 2.01 0.08 910 7.64 2296 2
2400-SR401-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.73 4.73 2.36 2.01 0.08 910 7.71 2307 2
2500-SR508-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.71 4.71 2.38 2.02 0.08 910 7.69 2303 2
2570-SR504-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.74 4.74 2.39 2.03 0.08 910 7.73 2309 2
2550-SR501-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.78 4.78 2.40 2.04 0.08 910 7.79 2319 2
2000-SR001-SWB01 Switchboard/Incomer
SUB003 Feeder to
KV 4.86 4.86 2.41 2.05 0.08 910 7.87 2330 2
59
9.6 Appendix F – Arc flash study results for RMUs and switchboards
downstream
Table 22: Arc flash study results for the RMUs based on the existing settings
Table 23: Arc flash study results for the sizer drives switchboards based on the existing protection settings
Table 24: Arc flash study results for the VSDs based on the existing protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
RMU12 Upstream (SUB003)
4.86 4.86 2.42 2.06 0.08 910 7.93 2340 2
RMU29 Upstream (SUB003)
4.81 4.81 2.40 2.04 0.08 910 7.85 2327 2
RMU13 Upstream (SUB003)
4.78 4.78 2.39 2.03 0.08 910 7.80 2320 2
RMU17 Upstream (SUB003)
4.72 4.72 2.37 2.01 0.08 910 7.70 2305 2
RMU11 Upstream (SUB002)
4.58 4.58 2.46 2.09 0.08 910 7.47 2270 2
RMU14 Upstream (SUB002)
4.50 4.50 2.43 2.07 0.08 910 7.35 2252 2
RMU15 Upstream (SUB002)
4.45 4.45 2.41 2.05 0.08 910 7.26 2238 2
RMU16 Upstream (SUB002)
4.36 4.36 2.36 2.01 0.08 910 7.11 2216 2
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
SR152-SWB01 Incomer
Upstream 3.43 3.39 2.55 2.15 0.92 910 4.79 3775 2
SR152-SWB01 Switchboard
Incomer 3.43 3.39 2.55 2.15 0.52 910 2.71 2100 1
SR122-SWB01 Incomer
Upstream 3.58 3.53 2.67 2.25 0.77 910 4.21 3304 2
SR122-SWB01 Switchboard
Incomer 3.58 3.53 2.67 2.25 0.52 910 2.83 2198 1
SR112-SWB01 Incomer
Upstream 3.57 3.53 2.67 2.25 0.77 910 4.21 3306 2
SR112-SWB01 Switchboard
Incomer 3.57 3.53 2.67 2.25 0.52 910 2.82 2194 1
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
CV113-VSD01 Incomer
Upstream 25.68 21.18 24.23 17.04 1.05 610 49.75 7647 X
CV113-VSD01 Switchboard
Incomer 25.68 21.18 24.23 17.04 0.09 610 4.26 1443 2
CV123-VSD01 Incomer
Upstream 25.70 21.20 24.25 17.04 1.05 610 49.79 7652 X
CV123-VSD01 Switchboard
Incomer 25.70 21.20 24.25 17.04 0.09 610 4.27 1444 2
CV763-VSD02 Incomer
Upstream 25.43 20.10 23.58 16.60 1.11 610 52.08 7888 X
CV763-VSD02 Switchboard
Incomer 25.43 20.10 23.58 16.60 0.09 610 4.22 1433 2
CV125-VSD01 Incomer
Upstream 25.30 20.89 23.48 16.54 1.05 610 49 7569 X
CV125-VSD01 Switchboard
Incomer 25.30 20.89 23.48 16.54 0.09 610 4.20 1428 2
CV705-VSD03 Incomer
Upstream 25.47 21.02 23.62 16.63 1.05 610 49.34 7604 X
CV705-VSD03 Switchboard
Incomer 25.47 21.02 23.62 16.63 0.09 610 4.23 1435 2
CV704-VSD01 Incomer
Upstream 25.65 21.16 23.82 16.76 1.05 610 49.71 7643 X
CV704-VSD01 Switchboard
Incomer 25.65 21.16 23.82 16.76 0.09 610 4.26 1442 2
CV704-VSD02 Incomer
Upstream 25.66 21.17 23.82 16.76 1.05 610 49.72 7644 X
CV704-VSD02 Switchboard
Incomer 25.66 21.17 23.82 16.76 0.09 610 4.26 1442 2
60
Table 25: Arc flash study results for 0.4kV switchboards based on the existing protection settings
(1) Protection settings not available.
CV704-VSD03 Incomer
Upstream 25.54 21.07 23.82 16.76 1.05 610 49.48 7619 X
CV704-VSD03 Switchboard
Incomer 25.54 21.07 23.82 16.76 0.09 610 4.26 1442 2
CV153-VSD01 Incomer
Upstream 25.00 20.65 23.21 16.35 1.05 610 48.41 7506 X
CV153-VSD01 Switchboard
Incomer 25.00 20.65 23.21 16.35 0.09 610 4.15 1416 2
CV763-VSD01 Incomer
Upstream 17.92 15.05 17.49 12.50 0.89 610 29.14 5319 4
CV763-VSD01 Switchboard
Incomer 17.92 15.05 17.49 12.50 0.09 610 2.95 1123 1
CV705-VSD02 Incomer
Upstream 18.83 15.78 18.32 13.06 0.84 610 29.01 5303 4
CV705-VSD02 Switchboard
Incomer 18.83 15.78 18.32 13.06 0.09 610 3.10 1162 1
CV705-VSD01 Incomer
Upstream 18.80 15.75 18.28 13.04 0.84 610 29.03 5305 4
CV705-VSD01 Switchboard
Incomer 18.80 15.75 18.28 13.04 0.09 610 3.10 1161 1
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE
SR701-MCC01 Incomer
Upstream 20.57 10.14 20.48 8.59 1.16 610 24.79 4766 3
SR701-MCC01 Switchboard
Incomer 20.57 10.14 20.48 8.59 6.5 610 116.54 13629 X
SR029-MCC01 Incomer
Upstream 29.72 13.60 29.07 11.36 1.37 610 40.19 6616 X
SR029-MCC01 Switchboard
Incomer(1) 29.72 13.60 29.07 11.36 610
SR706-MCC01 Incomer
Upstream 13.55 7.27 13.42 6.14 1.07 610 15.96 3535 3
SR706-MCC01 Switchboard
Incomer 13.55 7.27 13.42 6.14 0.46 610 6.86 1993 2
SR705-MCC01 Incomer
Upstream 20.40 10.07 19.78 8.36 4.45 610 94.42 11815 X
SR705-MCC01 Switchboard
Incomer 20.40 10.07 19.78 8.36 0.43 610 9.12 2418 3
SR703-MCC01 Incomer
Upstream 13.53 7.26 13.38 6.12 1.07 610 15.94 3531 3
SR703-MCC01 Switchboard
Incomer 13.53 7.26 13.38 6.12 0.43 610 6.40 1901 2
SR151-MCC01 Incomer
Upstream 36.17 15.90 33.63 12.75 2 610 69.84 9627 X
SR151-MCC01 Switchboard
Incomer(1) 36.17 15.90 33.63 12.75 610
SR121-MCC01 Incomer
Upstream 36.2 15.91 34.36 12.97 2.01 610 69.89 9632 X
SR121-MCC01 Switchboard
Incomer 36.2 15.91 34.36 12.97 0.09 610 3.13 1169 1
SR111-MCC01 Incomer
Upstream 36.15 15.89 34.29 12.95 2 610 69.80 9624 X
SR111-MCC01 Switchboard
Incomer 36.15 15.89 34.29 12.95 0.09 610 3.13 1168 1
SR707-MCC01 Incomer
Upstream 45.36 19.04 42.39 15.33 0.60 610 25.33 4836 4
SR707-MCC01 Switchboard
Incomer 45.36 19.04 42.39 15.33 0.43 610 18.16 3858 3
61
9.7 Appendix G – GE LV circuit breaker curve
Refer to the relevant section from the “Operation and Maintenance Manual” for the MPRO 50 trip
unit to understand how to determine the total clearing time from the curve seen in Figure 11.
Figure 11: GE LV circuit breaker curve (approval pending [39]
62
9.8 Appendix H – Maintenance mode protection settings
Table 26: Settings and location of the three maintenance switches
MS at SUB801 11kV Switchboard incomer
50P2 pickup 2550A
Time setting 0
MS at SUB002 33kV switchboard incomer
50P1 pickup 1600 A
Time setting 0
MS at SUB003 33kV switchboard incomer
50P1 pickup 1600 A
Time setting 0
63
9.9 Appendix I – Arc flash study results for Stockyard based on the
proposed solutions
Table 27: Arc flash study results for 0.4kV switchboards installed at the Stockyard based on the proposed protection settings
Highlighted in red are the protection settings changes that need to be implemented to reduce the arc
flash incident energy.
Table 28: Proposed protection settings for the Stockyard 0.4kV switchboards incomers
SUB801 MCC Incomer SUB901 MCC Incomer SK801 MCC Incomer(1) SK802 MCC Incomer RC901 MCC Incomer
ICT 2500 2500 1250 800
In (xICT) 1 1 1 1
LT (x In) 0.9 0.9 0.85 0.8
LT s 10 10 20 2.5
ST 3 3 8kA 6 6
ST s 0.2 0.2 0.2 0.2 0.2
INST 8 6 10 12
(1) Protection settings to ensure incident energy is less than 8 cal/cm2.
Table 29: Arc flash study results for the Stockyard 11kV switchboards based on the proposed protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
SUB801-SWB01
Incomer CB Remote operation will eliminate arc flash hazard.
SUB801-SWB01
Switchboard Incomer 30.54 13.89 29.80 11.58 0.23 610 6.91 2002 2 No
SK801-MCC01 Incomer CB
Remote operation will eliminate arc flash hazard.
SK801-MCC01 Switchboard
Incomer 28.42 13.12 27.07 10.73 0.23 610 5.36 1685 2 No
SK802-MCC01 Incomer CB
Remote operation will eliminate arc flash hazard.
SK802-MCC01 Switchboard
Incomer 22.74 10.98 21.94 9.08 0.23 610 5.36 1685 2 No
RC901-MCC01 Incomer CB
Remote operation will eliminate arc flash hazard.
RC901-MCC01 Switchboard
Incomer 15.35 8.03 15.31 6.81 0.23 610 3.82 1339 1 No
SUB901-MCC01
Incomer CB Remote operation will eliminate arc flash hazard.
SUB901-MCC01
Switchboard Incomer 29.48 13.51 28.61 11.21 0.23 610 6.70 1961 2 No
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
SUB901-SWB01
Incomer CB Upstream 12.18 11.78 7.92 6.56 0.25 910 5.00 3946 2 No
SUB901-SWB01
Switchboard Incomer 12.18 11.78 7.92 6.56 0.25 910 5.00 3946 2 No
SUB801-SWB01
Incomer CB Remote operation will eliminate arc flash hazard.
SUB801-SWB01
Switchboard Incomer 19.26 18.49 11.18 9.21 0.08 910 2.61 2019 1 Yes
64
Table 30: Proposed protection settings for Stockpile 11kV switchboards incomers
Protection Device Location Relay CTR 51P 50P
Feeder to SUB901 11kV switchboard
SUB801 SEL751A 1000 CS – 0.52
C2 TD – 0.75
Pickup – 4 Time setting – 0.20 s
Incomer of main SUB901 11kV switchboard
SUB901 SEL751A 1000 CS-0.94
C2 TD – 0.69
Pickup – 4 Time setting – 0.20 s
65
9.10 Appendix J – Arc flash study results for the Firetail OPF based on the
proposed solutions
Table 31: Arc flash study results for Firetail 0.4kV switchboards based on the proposed protection settings
Highlighted in red are the protection settings changes that need to be implemented to reduce the arc
flash incident energy.
Table 32: Proposed protection settings for Firetail 0.4kV switchboards incomers
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
SR203-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR203-MCC01 Switchboard
Incomer 37.59 16.39 35.38 13.28 0.18 610 6.46 1914 2 No
SR104-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR104-MCC01 Switchboard
Incomer 37.54 16.38 35.27 13.24 0.18 610 6.46 1912 2 No
SR102-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR102-MCC01 Switchboard
Incomer 42.39 18.04 35.34 13.27 0.18 610 7.17 2053 2 No
SR502-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR502-MCC01 Switchboard
Incomer 39.80 17.16 35.34 13.27 0.18 610 6.79 1979 2 No
SR402-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR402-MCC01 Switchboard
Incomer 40.93 17.54 35.37 13.28 0.18 610 6.96 2011 2 No
SR303-MCC02 Incomer
Remote operation will eliminate arc flash hazard.
SR303-MCC02 Switchboard
Incomer 38.95 16.86 35.32 13.26 0.18 610 6.67 1954 2 No
SR303-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR303-MCC01 Switchboard
Incomer 41.07 17.59 35.33 13.26 0.18 610 6.98 2015 2 No
SR203-MCC01
Incomer SR104-MCC01
Incomer SR102-MCC01
Incomer SR502-MCC01
Incomer SR402-MCC01
Incomer SR303-MCC02
Incomer SR303-MCC01
Incomer
Rating 3200 3200 3200 3200 3200 3200 3200
LT pickup 0.75 x Ie 0.75 x Ie 0.75 x Ie 0.75 x Ie 0.75 x Ie 0.75 x Ie 0.75 x Ie
LT Band C2 C2 C2 C2 C2 C2 C2
Ir 2400 2400 2400 2400 2400 2400 2400
ST pickup 5 x Ir 5 x Ir 5 x Ir 5 x Ir 5 x Ir 5 x Ir 5 x Ir
ST Band 5 5 5 5 5 5 5
INST pickup 10 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie
66
Table 33: Arc flash study results for Firetail 33kV switchboards based on the proposed maintenance mode protection settings
Equipment Clearing Device
location
Max Bolted Fault
Current (kA)
Max Arc
Current (kA)
Min Bolted Fault
Current (kA)
0.85 x Min Arc Current
(kA)
Total Clearing time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
2000-SUB001-RMU01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.59 4.59 2.47 2.10 0.08 910 7.46 2269 2 Yes
2200-SR201-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.57 4.57 2.47 2.10 0.08 910 7.43 2262 2 Yes
2100-SR103-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.45 4.45 2.42 2.06 0.08 910 7.25 2236 2 Yes
2100-SR101-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.53 4.53 2.45 2.08 0.08 910 7.37 2256 2 Yes
2550-SR501-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.54 4.54 2.45 2.08 0.08 910 7.39 2258 2 Yes
2400-SR401-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.52 4.52 2.46 2.09 0.08 910 7.42 2263 2 Yes
2300-SR301-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.52 4.52 2.44 2.07 0.08 910 7.35 2252 2 Yes
2000-SR001-SWB01 Switchboard/Incomer
SUB002 33kV switchboard
incomer 4.59 4.59 2.47 2.10 0.08 910 7.48 2273 2 Yes
67
9.11 Appendix K – Arc flash study results for the Firetail OPF based on the
proposed solutions
Table 34: Arc flash study results for KV 0.4kV switchboards based on the proposed protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault
Current (kA)
0.85 x Minimum
Arc Current
(kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
2300-SR303-MCC03 Incomer
Remote operation will eliminate arc flash hazard.
2300-SR303-MCC03 Switchboard
Incomer 36.34 15.96 34.88 13.12 0.20 610 6.98 2015 2 No
2300-SR303-MCC02 Incomer
Remote operation will eliminate arc flash hazard.
2300-SR303-MCC02 Switchboard
Incomer 39.57 17.08 35.23 13.23 0.20 610 7.51 2118 2 No
2300-SR303-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2300-SR303-MCC01 Switchboard
Incomer 38.91 16.85 32.10 12.29 0.20 610 7.40 2098 2 No
2100-SR104-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2100-SR104-MCC01 Switchboard
Incomer 36.81 16.12 35.22 13.23 0.20 610 7.05 2030 2 No
2100-SR102-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2100-SR102-MCC01 Switchboard
Incomer 43.42 18.39 35.26 13.24 0.18 610 7.32 2082 2 No
2200-SR203-MCC02 Incomer
Remote operation will eliminate arc flash hazard.
2200-SR203-MCC02 Switchboard
Incomer 39.19 16.95 35.05 13.18 0.20 610 7.45 2106 2 No
2200-SR203-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2200-SR203-MCC01 Switchboard
Incomer 40.49 17.39 34.49 13.01 0.20 610 7.66 2147 2 No
2700-SR702-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2700-SR702-MCC01 Switchboard
Incomer 37.37 16.32 35.78 13.40 0.20 610 7.15 2049 2 No
2400-SR402-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2400-SR402-MCC01 Switchboard
Incomer 39.91 17.19 34.81 13.11 0.20 610 7.56 2129 2 No
2500-SR509-MCC03 Incomer
Remote operation will eliminate arc flash hazard.
2500-SR509-MCC03 Switchboard
Incomer 33.56 14.98 32.13 12.30 0.20 610 6.51 1924 2 No
2500-SR509-MCC02 Incomer
Remote operation will eliminate arc flash hazard.
2500-SR509-MCC02 Switchboard
Incomer 38.50 16.71 35.28 13.25 0.20 610 7.33 2085 2 No
2500-SR509-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2500-SR509-MCC01 Switchboard
Incomer 37.94 16.51 35.26 13.24 0.20 610 7.24 2067 2 No
2570-SR505-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2570-SR505-MCC01 Switchboard
Incomer 37.18 16.25 35.16 13.21 0.20 610 7.12 2043 2 No
2550-SR503-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
2550-SR503-MCC01 Switchboard
Incomer 39.40 17.02 35.31 13.26 0.20 610 7.48 2113 2 No
68
Highlighted in red are the protection settings changes that need to be implemented to reduce the arc
flash incident energy.
Table 35: Proposed protection settings for KV 0.4kV incomer
SR303-MCC01 Incomer
SR303-MCC02 Incomer
SR303-MCC03 Incomer
SR104-MCC01 Incomer
SR102-MCC01 Incomer
SR203-MCC01 Incomer
SR203-MCC02 Incomer
Rating 3200 3200 3200 3200 3200 3200 3200
LT pickup 0.75 0.75 0.75 0.75 0.75 0.75 0.75
LT Band C-Min C-Min C-Min C-Min C-Min C-Min C-Min
Ir 2400 2400 2400 2400 2400 2400 2400
ST pickup 4 x Ir 4 x Ir 4 x Ir 4 x Ir 4 x Ir 4 x Ir 4 x Ir
ST Band 6 6 6 6 5 6 6
INST pickup 10 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie
SR702-MCC01 Incomer
SR402-MCC01 Incomer
SR509-MCC03 Incomer
SR509-MCC02 Incomer
SR509-MCC01 Incomer
SR505-MCC01 Incomer
SR503-MCC01 Incomer
Rating 3200 3200 3200 3200 3200 3200 3200
LT pickup 0.75 0.75 0.75 0.75 0.75 0.75 0.75
LT Band C-Min C-Min C4 C4 C4 C-Min C-Min
Ir 2400 2400 2400 2400 2400 2400 2400
ST pickup 4 x Ir 4 x Ir 4 x Ir 4 x Ir 4 x Ir 4 x Ir 4 x Ir
ST Band 6 6 6 6 6 6 6
INST pickup 10 x Ie 10 x Ie 9 x Ie 10 x Ie 10 x Ie 10 x Ie 10 x Ie
Table 36: Arc flash study results for KV 33kV switchboards based on the proposed maintenance mode protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault Current (kA)
Maximum Arc Current
(kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time
(s)
Working Distance
(mm)
Incident
Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
2300-SR301-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.75 4.75 2.37 2.01 0.08 910 7.74 2312 2 Yes
2100-SR103-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.72 4.72 2.37 2.01 0.08 910 7.70 2305 2 Yes
2100-SR101-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.73 4.73 2.38 2.02 0.08 910 7.72 2308 2 Yes
2200-SR201-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.75 4.75 2.38 2.02 0.08 910 7.75 2312 2 Yes
2700-SR701-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.68 4.68 2.36 2.01 0.08 910 7.64 2296 2 Yes
2400-SR401-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.73 4.73 2.36 2.01 0.08 910 7.71 2307 2 Yes
2500-SR508-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.71 4.71 2.38 2.02 0.08 910 7.69 2303 2 Yes
2570-SR504-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.74 4.74 2.39 2.03 0.08 910 7.73 2309 2 Yes
2550-SR501-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.78 4.78 2.40 2.04 0.08 910 7.79 2319 2 Yes
2000-SR001-SWB01 Switchboard/Incomer
SUB003 33kV switchboard
incomer
4.86 4.86 2.41 2.05 0.08 910 7.87 2330 2 Yes
69
9.12 Appendix L – Arc flash study results for RMUs based on proposed
solutions
Table 37: Arc flash study results for the RMUs based on the proposed maintenance mode protection settings
Equipment Clearing Device
Location
Maximum Bolted Fault
Current (kA)
Maximum Arc
Current (kA)
Minimum Bolted Fault Current (kA)
0.85 x Minimum
Arc Current (kA)
Total Clearing Time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm)
PPE
MS
RMU12
SUB003 33kV switchboard
incomer
4.86 4.86 2.42 2.06 0.08 910 7.93 2340 2 Yes
RMU29
SUB003 33kV switchboard
incomer
4.81 4.81 2.40 2.04 0.08 910 7.85 2327 2 Yes
RMU13
SUB003 33kV switchboard
incomer
4.78 4.78 2.39 2.03 0.08 910 7.80 2320 2 Yes
RMU17
SUB003 33kV switchboard
incomer
4.72 4.72 2.37 2.01 0.08 910 7.70 2305 2 Yes
RMU11
SUB002 33kV switchboard
incomer
4.58 4.58 2.46 2.09 0.08 910 7.47 2270 2 Yes
RMU14
SUB002 33kV switchboard
incomer
4.50 4.50 2.43 2.07 0.08 910 7.35 2252 2 Yes
RMU15
SUB002 33kV switchboard
incomer
4.45 4.45 2.41 2.05 0.08 910 7.26 2238 2 Yes
RMU16
SUB002 33kV switchboard
incomer
4.36 4.36 2.36 2.01 0.08 910 7.11 2216 2 Yes
Table 38: Arc flash study results for 0.4kV switchboards based on the proposed protection settings
Equipment Clearing Device
location
Max Bolted Fault
Current (kA)
Max Arc Current
(kA)
Min Bolted Fault
Current (kA)
0.85 x Min Arc Current
(kA)
Total Clearing time (s)
Working Distance
(mm)
Incident Energy
(𝒄𝒂𝒍
𝒄𝒎𝟐)
Arc Flash Boundary
(mm) PPE MS
SR701-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR701-MCC01 Switchboard
Incomer 20.57 10.14 20.48 8.59 0.23 610 4.92 1589 2 No
SR029-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR029-MCC01 Switchboard
Incomer 29.72 13.60 29.07 11.36 0.26 610 7.63 2141 2 No
SR706-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR706-MCC01 Switchboard
Incomer 13.55 7.27 13.42 6.14 0.23 610 3.43 1245 1 No
SR705-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR705-MCC01 Switchboard
Incomer 20.40 10.07 19.78 8.36 0.23 610 4.88 1581 2 No
SR703-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR703-MCC01 Switchboard
Incomer 13.53 7.26 13.38 6.12 0.23 610 3.43 1243 1 No
SR151-MCC01 Incomer
Remote operation will eliminate arc flash hazard.
SR151-MCC01 Switchboard
Incomer 36.17 15.90 33.63 12.75 0.09 610 3.13 1169 1 No
SR121-MCC01 Incomer
Remote operation will eliminate arc flash hazard. SR111-MCC01
Incomer
SR707-MCC01 Incomer
SR707-MCC01 Switchboard
Incomer 45.36 19.04 42.39 15.33 0.13 610 5.49 1712 2 No
RBS MCC Incomer 7.88 4.72 7.76 3.96 0.26 610 2.43 985 1 No
70
Highlighted in red are the protection settings changes that need to be implemented to reduce the arc
flash incident energy.
Table 39: Proposed protection settings for LV incomers
SR706-MCC01
Incomer SR705-MCC01
Incomer SR703-MCC01
Incomer SR701-MCC01
Incomer SR151-MCC01
Incomer(1)
SR029-MCC01
Incomer(1)
RBS Incomer(1)
SR707-MCC01 Incomer
ICT 1250 1600 1250 1600 3200 1600
In (xICT) 0.8 1 0.8 1 0.9 1
LT (x In) 1 0.8 1 1 C12 0.85
LT s 10 10 10 10 2880 10
ST 4 4 4 4 3 8kA 2kA 6
ST s 0.2 0.2 0.2 0.2 1 0.2 0.2 0.1
INST 12 10 12 10 5 16
71
9.13 Appendix M – Proposed protection settings to resolve grading
problems found
Highlighted in red are the protection settings changes that need to be implemented to reduce the arc
flash incident energy.
Table 40: Proposed settings for protection devices for the main Firetail 33kV switchboard (2000-SR001)
Location Relay CTR 51P CS Curve TD 50P
Feeders to main Firetail Switchboard
(2000-SR001) SUB002 GE F650 600 0.81 Curve A 0.23 Off
Incomer for main Firetail switchboard (2000-SR001)
Main Firetail switchboard
(2000-SR001) SEL751A 600 0.81 C1 0.23 Off
Table 41: Proposed settings for protection devices for the main KV 33kV switchboard (2000-SR001)
Table 42: Proposed settings for feeders to RMUs for correct coordination between protection devices
Location Relay CTR 51P CS Curve TD 50P
Feeders To main KV Switchboard
(2000-SR001) SUB003 GE F650 600 1.2 Curve A 0.19
De-activate
Incomers for main KV switchboard (2000-SR001)
KV SEL751A 1200 0.6 C1 0.19 off
Location Relay CTR 51P 50P
Feeder To RMU14
SUB002 (SWB05-CB07)
GE F650 300 CS – 1
Curve A TD – 0.1
Pickup – 6 Time setting – 0.25 s
Feeder To RMU11
SUB002 (SWB05-CB06)
GE F650 300 CS – 0.48 Curve A TD – 0.1
Pickup – 2.9 Time setting – 0.25 s
Feeder To RMU13
SUB003 (SWB06-CB06)
GE F650 300 CS – 1
Curve A TD – 0.1
Pickup – 6 Time setting – 0.25 s
Feeder To RMU12
SUB003 (SWB06-CB07)
GE F650 300 CS – 0.48 Curve A TD – 0.1
Pickup – 2.9 Time setting – 0.25 s