Mitch Bradt, PE Univ. of Wisconsin-Madison · NESC- IEEE/ANSI-C2 National Electrical Safety Code....

1May 25, 2011 Wind Plant Collector System Design WINDPOWER2011

Intro to IEEE PES Wind Plant Collector System Design working group

and Today’s Panel

Mitch Bradt, PEUniv. of Wisconsin-MadisonIEEE PES Wind Plant Collector Design wg

Chair

May 25, 2011 Wind Plant Collector System Design WINDPOWER2011


GE Energy2.5 MW

Wind Turbine

184 m

147 m

192 m183 m

150 m RE Power5 MWWind

Turbine

169 m

Wind Energy is Big – Size and Business


General Layout of the Collector System

Inside the Nacelle

DD

Converter

GeneratorProtection

To Adjacent WTG orSubstation Feeder Breaker

Pad-MountedTransformer

(Internal or External)

Tower Voltage 575V to 35kV

(Cable or Bus)


Generator Step Up Transformer

Voltage stepped-up to 34.5kV; connected to collector


Transformer located in Nacelle


Feeder Conductors—Trench Installation


Wind Plant Collector Substation


Feeder Terminations, grounding xfmrs,34.5kV breakers and bus


Substation Interconnection Transformer

Secondary bushing: 34.5 kV

Primary bushing: 345kV

“Zig-Zag” grounding transformer


IEEE Wind Plant Collector Design Working Group Scope:

• Serve as a focal point within the Institute of Electrical and Electronic Engineers (IEEE) for addressing issues related to the design of collector systems for wind plants, including tradeoffs associated with overhead vs. underground lines, grounding, distribution equipment applications, cost and reliability tradeoffs for the unique characteristics of this energy resource, protection, reactive compensation, and SCADA application.

• Conduct activities to promote the sharing of knowledge and experience among diverse organizations working on similar issues through the conduct of studies, symposia, workshops, paper session, panel sessions, and tutorials.

• Publish working group papers to document results of working group activities and to share working group positions on issues related to the design of collector systems for wind plants.

• Website: http://grouper.ieee.org/groups/td/wind/– Links to: Papers, Presentations, Meeting Announcements, Minutes


Organization of the WPCSD wg The WPCSD wg was stood up in April 2008 at the

IEEE T&D Conf. & Expo in Chicago

IEEE PES

T&D Cmte

Integration of

Renewable Energy into the

T&D GridSub-cmte

Wind Plant Collector

Sys Design wg


Working Group

Many wonderful volunteers

Current Officers:

For resources, please see our website for papers and presentations:– http://grouper.ieee.org/groups/td/wind/

or use QR …

Chair Mitch Bradt – Univ. of Wisconsin-Madison

Vice-Chair Wayne Dilling – Mortenson Construction

Secretary/Web

Michael Starke – Oak Ridge National Lab


Available Resourcespublished 2009

WPP Collector System Design Considerations Characteristics of WTGs for WPP WPP Grounding, Overvoltage Protection &

Insulation Coordination Reactive Power Compensation for WPP WPP Substation and Collector System

Redundancy, Reliability and Economics



WPP Collector System Design Considerations



WPP Grounding, Overvoltage Protection & Insulation Coordination

-100

-50

0

50

100

100 200 300 400 500 600

34.5kV Collector Circuit #1 Voltage

Volta

ge (k

V)

Time (ms)

Phase A Phase B Phase C

Fault Occurs

Breaker Trips

Temporary Overvoltage



Reactive Power Compensation for WPP

1.25 MVAR

33 kV

2.5 MVA0.48/34.5 kV

1.25 MVAR



WPP Substation and Collector System Redundancy, Reliability and Economics

Bus Type Cost Reliability EHV MV

Single 46.7% Low X X

Sectionalized 57.0% Low X X

Main & Transfer 66.8% Low X X

Ring 53.3% Medium X

Breaker-and-a-Half 73.8% High X

Double Breaker –Double Bus

100% High X



Arc-Flash Hazards in WPP Design and Application of Cables and OH Lines

for WPP Power Transformer Application for WPP WPP Collector System Fault Protection and

Coordination



Arc-Flash Hazards in WPP



Design and Application of Cables and OH Lines for WPP

Jacket Insulation

Concentricneutral or ‘shield’

Insulationshield

Conductor

Conductorshield



Power Transformer Application for WPP



WPP Collector System Fault Protection & Coord.

Tran

sform

er

Zon

e

Util

ity

Inte

rcon

nect

ion

Zon

e

Bus

Diff

eren

tial

Zon

e

Collector Zone


… and more comingto be published at PES GM in Detroit, July 2011

Harmonics and Resonance Issues in WPP WPP SCADA and Controls WPP Testing and Commissioning


Presenters at Today’s Panel

Wayne Dilling – MortensonNEC and NESC Considerations from a Construction Perspective

Chris Brooks – S&C ElectricNational Electrical Safety Code Applicability in Wind Farms

Abdou Sana– RES AmericasNational Electrical Code Applicability to Wind Power Plant Collection

Systems and Grounding Design


Logistics

Presentations are available through AWEA Also available through our website

QUESTIONS are encouraged, but please hold until after each speaker finishes

Speakers will be available after panel for discussion

– http://grouper.ieee.org/groups/td/wind/

or use QR …

Impacts of NEC/NESC on Wind PlantsA Construction Perspective

Wayne Dilling, PEMortenson Construction

Impacts of NEC/NESC on Wind Plants


Introduction

• Code Enforcement

• Applicable Codes

• Code Compliance Challenges for Wind Plants


Code Enforcement on Wind Plants

Defined by State, County, and/or local jurisdictions• Construction permit application process will usually

define (not always…)• Authority Having Jurisdiction (AHJ)

– Will have ultimate code enforcement on site (many sites will not have any known or active AHJ)


Code Enforcement on Wind PlantsAHJ (as defined by NFPA 70)“An organization, office, or individual responsible for

enforcing the requirements of a code or standard, or for approving equipment, materials, an installation, or a procedure.”

May be a federal, state, local, or other regional department or individual such as a fire chief, electrical inspector, or others having statutory authority.


Applicable CodesNESC- IEEE/ANSI-C2 National Electrical Safety Code

The purpose of the NESC is the practical safeguarding of persons during the installation, operation, or maintenance of electrical supply and communication lines, equipment, and associated work practices employed by a public or private electric supply, communications, railway, or similar utility in the exercise of its function as a utility.


Applicable CodesNESC- IEEE/ANSI-C2 National Electrical Safety Code

What Isn't CoveredNESC rules do not cover installations in mines, ships, railway rolling equipment, aircraft, or automotive equipment, or utilization wiring except as covered in Parts 1 and 3. For building utilization wiring requirements, see the National Electrical Code.

Clear Direction Right???


Applicable CodesNEC- NFPA 70- National Electrical Code

Article 90.2 SCOPE (A) CoveredThis code covers the installation of electrical conductors,

equipment, and raceways...equipment…for the following:– Public and private premises…– Industrial substations– Installation of conductors and equipment that connect

to the supply of electricity– Installations used by electric utilities that are not part

of a generating plant, substation, or control center.


Applicable CodesNEC- NFPA 70- National Electrical Code

Article 90.2 SCOPE (B) NOT COVERED

(5) Installations under the exclusive control of an electric utility…

(Most large scale wind plants are not under the exclusive control of an electric utility.)


Applicable CodesThe Simplistic View:

NESC: Covers High Voltage Work (transmission, substations, distribution)

NEC: Covers Public and private building wiring, typically 15kV and below. For a wind plant this seems to be more applicable to inside the tower.

Quote from Minnesota Regulatory Commission:“Most work under the jurisdiction of the NESC in Minnesota is

exempt from licensing and inspection requirements and therefore the NESC is minimally referenced by the ‘inspection’department”


Applicable CodesSo, Which Code Applies?

Ultimately OSHA (Occupational Safety and Health Administration)

Majority of Wind plant installations have chosen to comply with both NESC and the governing NFPA codes (inclusive of the NEC) since this provides the best chance of OSHA compliance


Code Compliance Challenges for Wind Plants

Many Wind Turbine components are produced outside of North America and originally adopted under European codes and standards.

Some examples:DIN- Deutches Institute Fur NormungIEC- International Electrotechnical Commission

Turbine suppliers often reference these standards and are required to be met under the Turbine Supplier Agreement (TSA)



Confined Spaces:

PtD- (Prevention through Design) can help eliminate this type of egress issue.

Photo from Redwood Kardon, Code Check Institute- published in EC&M Magazine March 2011



Clear Working Space:

Oil containment or trip hazard?

Photo from Redwood Kardon, Code Check Institute- published in EC&M Magazine March 2011



Substation Control Building or Electrical Equipment Enclosure?Confirm what, if any, building codes apply. An adjacent Utility owned switchyard control building may be exempt, but the wind plant control building may need to meet IBC or other local codes.



Grounding- Copper Vs. Copper Clad Steel

With rising copper costs (over $4/lb), Copper Clad Steel is being used by many wind plants for grounding as a cost reduction and theft deterrent.

Copper Clad steel is not recognized by the NEC but is allowed under the NESC.



Turbine Foundation Grounding- Step and Touch Potential

IEEE Standard 80 governs safety in substation grounding

•Is this the right application for wind towers?•Do Utility owned distribution equipment located in public places meet this requirement?

(OSHA 1910.269 App C-addresses Step & Touch also)



Use of DLO- Finely Stranded Wire and Lug application

NEC 110.14 requires connectors to be identified for the specific conductor class but the finely stranded DLO conductor may not fall in a defined NEC class for some sizes.


Conclusion

• Identify early in the design process who is designated as the AHJ (Authority Having Jurisdiction) and what codes will be enforced

• Ensure the wind turbine components that may come from other countries, will comply with U.S. and local codes that are applicable to the project site

• The wind industry is still vetting what codes should apply for specific installations. The IEEE “Wind Working Groups” are making steps to help define this.


Questions?

Wayne Dilling, Mortenson [email protected]

mailto:[email protected]�

http://www.mortenson.com/�

©2011

How to Apply Electrical Code Requirements for Large Wind Power Plants

National Electrical Safety Code (NESC) (ANSI/IEEE C2) Applicability in Wind Farms

May 25, 2011Christopher L. Brooks, P.E.Senior Consultant

(678) 427-0126

1628 Arden DriveMarietta, GA 30008

©2011

Types of Safety Codes and Regulations that Wind Power Plants Need to Follow• NESC (National Electrical Safety Code )• California – GO 95(OH) and GO 128(UG)

– Very similar to NESC• NEC (National Electrical Code)• Local requirements• Contract requirements• OSHA

©2011

Interaction of Safety and Construction Standards

800kV

50 V

240/120V

345kV

480/277V

1000V

138kV

69kV

230kV

500kV dc

500kV

46kV

12kV

LV

MV

HV

EHV

©2011


OSHA800kV

50 V

240/120V

345kV

480/277V

1000V

138kV

69kV

230kV

500kV dc

500kV

46kV

12kV

LV

MV

HV

EHV

©2011


OSHA800kV

50 V

240/120V

345kV

480/277V

1000V

138kV

69kV

230kV

500kV dc

500kV

46kV

12kV

LV

MV

HV

NESC & GO95+128

EHV

©2011


OSHA800kV

50 V

240/120V

345kV

480/277V

1000V

138kV

69kV

230kV

500kV dc

500kV

46kV

12kV

LV

MV

HV

NESC & GO95+128

NFPA 70E

EHV

©2011


OSHA800kV

50 V

240/120V

345kV

480/277V

1000V

138kV

69kV

230kV

500kV dc

500kV

46kV

12kV

LV

MV

HV

NESC & GO95+128

NFPA 70ENEC-NFPA 70

EHV

©2011


OSHA800kV

50 V

240/120V

345kV

480/277V

1000V

138kV

69kV

230kV

500kV dc

500kV

46kV

12kV

LV

MV

HV

NESC & GO95+128

NFPA 70ENEC-NFPA 70

Utility Safety Rules,Construction Standards, & Designs

Utility

Standards

EHV

©2011

Where the codes are to be used

• Substation– NESC – Mostly MV (34.5kV) and HV (69kV-230kV)

• Collector System– NESC or NEC? – MV – 34.5kV Ownership? Voltage Level? Best suited? Size?

• Wind turbine towers– NEC – Mostly LV (<1000V)

©2011

Basic Structure of the Electric SystemAnd Applicability of Safety Codes

Residential

Com. & Ind.

Electrical Utility

©2011


Residential

Com. & Ind.

Wind Farms

Electrical Utility

©2011


NESC

Residential

Com. & Ind.

Wind Farms

Electrical Utility

NEC

©2011

Jurisdiction is a Key • State and/or local governments have the jurisdictions over codes to

enforce– NESC Enacted only by state governments Coverage - generation plant to the meter Includes LV(<1000V), MV(< 46,000V), and HV&EHV(> 46,000V) Self-enforced by the utilities – three states inspect the utilities

– NEC Enacted by local governments and by some states Coverage in-building, premises and connections to utilities

– Mostly LV(<1000V)– Some MV(< 46,000V) – such as - campuses

Enforced by cities/counties/districts– Utilities - some times have enforcement responsibilities

– Gray area – MV(< 46,000V) systems at industrial plants, campuses, and now wind power plant

©2011

Existing 2007 NESC Purpose (010)

The purpose of these rules is the practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment.

These rules contain the basic provisions that are considered necessary for the safety of employees and the public under the specified conditions. This Code is not intended as a design specification or as an instruction manual.

©2011

Proposed 2012 NESC Purpose (010)A. The purpose of the National Electrical Safety Code (NESC) is practical safeguarding of

persons and property during the installation, operation, and maintenance of electric supply and communication lines and associated equipment. NESC rules are founded upon the fundamental principles used for safety of public and private utility facilitiesand good engineering practice throughout the world.

B. NESC rules contain the basic provisions, under specified conditions, that are considered necessary for the safety of the following: 1. The public,2. Utility workers (employees and contractors),3. Utility lines,4. Electric supply and communication equipment connected to utility lines and

structures, and5. Other facilities or premises adjacent to or containing utility lines and equipment.

C. NESC rules are intended to provide a standard of safe practices that can be adopted by public utilities, private utilities, state or local utility commissions or public service commissions, or other boards or bodies having control over safe practices employed in the design, construction, operation, or maintenance of electric supply, communication, street and area lighting, signal, or railroad utility installations.

…(continued)

©2011

Scope for NESCKey Word - Utility

• NEW 2012 NESC – New Scope and Definition of a utility.

• utility. An organization responsible for the engineering supervision (design, construction, operation, or and maintenance) of a public or private electric supply…

• private utility. A private utility is an entity that – (a) performs or provides one or more utility services to its own

facilities, … – (b) generate or transmit power that is delivered to another

utility.

©2011

NESC - Top Level

NESC

Section 2Definitions Part 1

Rules for the Installation and

Maintenance ofElectric

Supply Stationsand Equipment

Part 2Safety Rules for the

Installation and Maintenanceof

OverheadElectric Supply

and Communication Lines

Section 1Introduction

Part 3Safety Rules for the

Installation and Maintenanceof

UndergroundElectric Supply

and Communication Lines

Part 4Rules for the

Operationof

Electric Supply andCommunications Lines and

Equipment

Section 9Grounding Methods

Section 3References

Part 1 Part 2 Part 3 Part 4

Sect 9

©2011

Where NESC rules are ApplicableSubstation

• Section 9 – grounding– Ground grid – (96B) – IEEE 80-2000– Fence grounding (92E + 93C6)

• Part 1 – Power Plants and Substations– Signage (110A1)– Conductor clearances inside substation (124’s)– Transformer clearances (150’s)– Circuit breakers (170’s)– Fence clearance (110A1+2)– Illumination (111)– Identification (128)– Overcurrent Protection (161A)– Conductor terminations (164)

©2011

Where NESC rules are Applicable Substation

• Part 3 – Underground conductors and structures– Excavation, ducts, vaults, etc (321-323)– Cables in manholes and vaults (340s)– Underground Equipment (380s)

• Part 4 – Work Safety– Arc Flash and risk (410A)– Personal precautions (420s) - definition of “qualified”, etc. Tools, ladders, fall, fire extinguishers, etc. Excavation, ventilation, flames, identification, etc.

– Minimum Approach Distances (MAD) – (441) Hot line work, tools, cover-ups, barehand, PPE, etc.

– Switching Control Procedures (442)

©2011

Example - Live Conductor ClearancesTable 124-1

Source: 2007 Edition of the National Electrical Safety Code, NY,NY

©2011

Where NESC rules are Applicable Collector System

• Section 9 – grounding – Must be multi-grounded – four(4) times/mile (96C)– If overhead – pole grounding rules (97)– If overhead – communications (97G) bond with any neutral conductor NOT with a static wire conductor

• Part 1 – Power Plants, Substations, and Field pad-mounted sites– Transformer clearances (150s)– Metal enclosed switchgear (180s)– Conductor terminations (164)

• Part 2 – Overhead conductors– Clearances (230s)– Mechanical limits in construction (250s)– Strength requirements in construction (260s and 270s)

©2011

Where NESC rules are Applicable Collector System

• Part 3 – Underground conductors– UG Clearances (320) - gas, water, sewer, com, etc.– Excavation, ducts, vaults, etc (321-323)– Cables in manholes and vaults (340s)– Buried Cables (350s)

• Part 4 – Work Safety– Arc Flash and risk (410A)– Personal precautions (420s) - definition of “qualified”, etc. Tools, ladders, fall, fire extinguishers, etc. Excavation, ventilation, flames, identification, etc.

– Minimum Approach Distances (MAD) – (441) Hot line work, tools, cover-ups, barehand, PPE, etc.

– Switching Control Procedures (442) – Equipment Safe Work (443-447) – grounding, LOTO, live work,

etc.

©2011

Example – Arc Flash Table - Table 410-1(1kV – 46kV)


©2011

Example – Arc Flash Table - Table 410-2(46kV – 800kV)


©2011

Example – Weather Loading 250B – Three Districts - Heights of poles/cond.


©2011

Example – Weather Loading 250D – Extreme Ice and Wind Loading >60 ft


©2011

Where NESC rules are Applicable Tower Vicinity

• Section 9 - grounding - Silent on a Ohm-age to ground– Manufacturer of WT & Tower – Some set ohm-age

• Part 1 – Power Plants, Substations, and Field pad-mounted sites– Metal enclosed switchgear (180s)– Rotating machines (130s)

©2011

Where NESC rules are Applicable Tower Vicinity

• Part 3 – Underground conductors– UG Clearances (320) - gas, water, sewer, com, etc.– Excavation, ducts, vaults, etc (321-323)– Cables in manholes and vaults (340s)– Buried Cables (350s)– Risers and Terminations (360s and 370s)– Underground Equipment (380s)

• Part 4 – Work Safety– Arc Flash and risk (410A)– Personal precautions (420s) – (definition of “qualified”, tools, ladders,

fall, fire extinguishers, excavation, ventilation, flames, etc.)– Minimum Approach Distances (MAD) – (441) – (Hot line work, tools,

cover-ups, barehand, PPE, etc.– Switching Control Procedures (442) – Equipment Safe Work (443-447) – grounding, LOTO, live work, etc.

©2011

Example – 2012 Proposed NESC Draft Table- for 50 to 1000V - Table

Source: Preprint Proposals for the 2012 Edition of the National Electrical Safety Code, NY,NY, 9/1/2009

©2011

Conclusions – My Thoughts

• Substation and Collector System – NESC (CA-GO95+GO128) Deep Rule set for HV and MV, Lines and Substations Proven use at these voltages Similar to a utility system

• Electrical Demark – Transition Point– NESC+NEC Transformer Outside - Secondary Cabinet Transformer Inside - First inside termination

• Wind Turbine and Tower– NEC & NFPA70E Deep Rule set for LV conductors and equipment Good equipment rules Similar to an industrial plant

©2011

Thank YouQuestions?

Christopher L. Brooks, P.E.Senior Consultant1628 Arden DriveMarietta, GA 30008678-427-0126

National Electrical Safety Code (NESC) (ANSI/IEEE C2) Applicability in Wind Farms

May 25, 2011 Wind Plant Collector System Design WINDPOWER2011 8282

NEC’s Applicability to Wind Power Plant (WPP) Collection Systems and Grounding Design.

Abdou SANA – Eng., M.Sc., Ph.D.Senior Electrical Design Engineer

AWEA May 2011


Content

• 1.0 Introduction• 2.0 Application of the NEC to

Parallel Cables3.0 Selection of Ampacity

• 4.0 Conclusions


1 Introduction

Purpose of the NEC (2011-version) Article 90.1.(A) “The practical safeguarding of persons

and property from hazards arising from the use of electricity”.


The Scope of the NEC (Rule 90.2(A)) Includes:

“The installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following:

1. Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings

2. Yards, lots, parking lots, carnivals, and industrial substations

3. Installations of conductors and equipment that connect to the supply of electricity

4. Installations used by the electric utility, such as office buildings, warehouses, garages, machine shops, and recreational buildings, that are not an integral part of a generating plant, substation, or control center..”.


The Scope of the NEC (Rule 90.2(B)) Excludes:1. Installations in ships, watercraft other than floating buildings, railway

rolling stock, aircraft, or automotive vehicles other than mobile homes and recreational vehicles...

2. Installations underground in mines and self-propelled mobile surface mining machinery and its attendant electrical trailing cable

3. Installations of railways for generation, transformation, transmission, or distribution of power used exclusively for operation of rolling stock or installations used exclusively for signaling and communications purposes

4. Installations of communications equipment under the exclusive control of communications utilities located outdoors or in building spaces used exclusively for such installations

5. Installations under the exclusive control of an electric utility where such installations :

• Consist of service drops or service laterals, and associated metering, or• Are on property owned or leased by the electric utility for the purpose of

communications, metering, generation, control, transformation, transmission, or distribution of electric energy.”

• Are located in legally established easements or rights-of-way or,• Are located by other written agreements either designated by or recognized

by public service commissions, utility commissions, or other regulatory agencies having jurisdiction for such installations…”


No mention of Wind Power Plant. NEC 2011 new Article 694 provides rules to

follow for safe wind turbine installation of “Small Wind Electric Systems” with WTG of 100 kW and less. The NEC is not yet covering the larger size

wind turbines and wind power generation plants.


NEC 2011 Article 694 Small Wind Electric Systems• Intended to Supply of a building or other structure• Consists of one or more WTGs with individual

WTG rated max 100 kW ~ 10 Houses (of 10kW each)

Utility Scale Wind WTG and Wind Power Plant• 1.5MW ~ 150 Houses• 4 MW ~ 400 Houses• 100 MW ~ 10,000 houses• 350 MW ~ 35,000 houses


Consultants include WPP in the scope of the NEC for the purpose of checking or approving design for third parties, because: WPP are not necessary a utility owned or under the

exclusive control of an electric utility and as such cannot be excluded (as per rule 90.2.(B).(5)).

Though WPP can be considered as an integral part of a generation plant, it is a distributed generation’s plant which is interconnected through a collection system which may be subject to public access and may be included as per rule 90.2(A)(1)to(4)

Application of the NEC to WPP results in possible conflicts in some cases. The following are two examples of controversies resulting from the application of the NEC

Consultants include WPP in the scope of the NECfor the purpose of checking or approving design forthird parties, because: WPP are not necessary a utility owned or under the

exclusive control of an electric utility and as such cannotbe excluded (as per rule 90.2.(B).(5)).

Though WPP can be considered as an integral part of ageneration plant, it is a distributed generation’s plantwhich is interconnected through a collection system whichmay be subject to public access and may be included asper rule 90.2(A)(1)to(4)

Application of the NEC to WPP results in possibleconflicts in some cases. The following are twoexamples of controversies resulting from theapplication of the NEC


2 Application of the NEC to Parallel Cables

Case where the WTG low voltage generation is stepped to the distribution level using a pad mounted transformer outside the tower as illustrated in Figure 1a &b.


2 Application of the NEC to Parallel Cables

Figure 1a; WTG tower & Pad-Mount Transformer


To the Nacelle

TowerPad Mount

Transformer

Conduits

Figure 1b: Illustration of a Typical Parallel LV Cables Connection between a WTG and a Pad Mounted Transformer –1x Grounding Conductor per Conduit


The following items needs to be designed, procured and installed: Pad mount transformer (PMT) --- Usually MV/LV

• The LV voltage is 690 Volts or 575volts and is Y-connected solidly grounded

• The MV voltage could vary from 12.5kV to 46kV (Most at 34.5kV) and may be Y solidly grounded, ungrounded Y or Delta

LV power cables connecting the WTG and the PMT trough the concrete structure of the tower As per NEC Article 310.10(H)(2) : “The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, equipment grounding conductor, or equipment bonding jumper shall comply with all of the following:• Be the same length• Have the same conductor material• Be the same size in circular mil area• Have the same insulation type• Be terminated in the same manner”

LV control cables in some cases A grounding conductor connecting the PMT and the WTG The Raceways (Cable Conduits) between the WTG and PMT


Application of Article 250.24.(C).(2) and Article 250.122. (F)

Article 250.122.(F) states that :“Where conductors are installed in parallel in multiple

raceways or cables as permitted in 310.10(H), the equipment grounding conductors, where used, shall be installed in parallel in each raceway or cable. Where conductors are installed in parallel in the same raceway, cable, or cable tray as permitted in 310.10(H), a single equipment grounding conductor shall be permitted. Equipment grounding conductors installed in cable tray shall meet the minimum requirements of 392.10(B)(1)(c). Each equipment grounding conductor shall be sized in compliance with 250.122.”


Article 250.24.(C).(2 ) applicable to sizing the grounding conductor in parallel conduits:

“If the ungrounded service-entrance conductors are installed in parallel in two or more raceways, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway, as indicated in 250.24(C)(1), but not smaller than 1/0 AWG...”


These two articles require that:• A grounding conductor be installed in each of the parallel

conduits as in Figure 1 • The size of the grounding conductor be based on the

phase conductors and the ampere rating of the overcurrent protection device.

For a typical WTG 2.3MW one can expect: • Phase Conductors:

• 6x 777kcmil copper per phase (1 in each conduit) • Grounding Conductors:

• 6x 500kcmil or 6x 600kcmil (1 per conduit) depending on fault level and clearing time.


• Why a redundant use of copper in the specific case of WPP where all the conduits are PVC (non conductive)?

• Is there any need for the Ground conductor in the same conduit as the phase conductors to be withstanding a ground fault happening inside the conduit?

• Does a ground fault inside the conduits means also that at least one of the phase conductors has an insulation failure and needs to be replaced?

• Is any fault inside the conduits destructive and will require a replacement of the destroyed conductor?

• A phase-to-ground fault at the end bus of the cable (a through fault) at the connecting bus-bar will have a low split factor which will result in a smaller sized conductor?

• One would expect a grounding conductor in a separate conduit as shown in Figure 2. For the typical 2.3MW WTG this would reduce the number of grounding cables from 6 to 1 or 2.


Figure 2: Illustration of a Typical Parallel LV Cables Connection between a WTG and a Pad Mounted Transformer – Grounding Conductors in a Separate Conduit

TowerPad Mount

Transformer

ConduitsTo the Nacelle


3 Selection of Ampacity –Articles 310.15(A)(2) and 310.60(B)(1)

Article 310.15(A)(2) applies to the selection of conductor rated 0 - 2000V (LV cables)

• “Where more than one ampacity applies for a given circuit length, the lowest value shall be used.

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less”

Article 310.60.(B)(1) states quite the same and is applicable to MV cables rated 2001- 35,000V.


Figure 3 Illustration of MV and LV Cable Entrance into a Typical Pad Mounted Transformer

MV Cables

Out

Pad Mount Transformer

< 10ft (3m) or 10% of L

L

Ampacity 1

Ampacity 2

MV Cables

In

WTGFondationConcrete

Dirt< 10ft (3m) or

10% of H

H

Ampacity 3

Ampacity 4

LV

MV

LV Cables


• LV cable coming from the foundation concrete will generally go through dirt before entering the Pad mounted transformer LV cabinet.

• There are two adjacent ampacity areas (Ampacity 3 and Ampacity 4 as shown in Figure 3) that need to be examined.

• Ampacity 4 (in concrete) > Ampacity 3 (in dirt)

Applying rule 310.15.(A).(2) will allow using the higher ampacity of cable embedded in concrete in most of the application where the pad mount is sitting close (<10 ft) to or on the concrete foundations.


Another area where the application of rule 310.60.(B)(1) may lead to controversy is the MV side of the pad mounted transformer (Figure 3)

• The MV cables to or from the pad mounted transformer are subject to a change of ampacity at the vicinity of the pad mounted transformer.

• Ampacity 1>Ampacity 2 (de- rating due to proximity and mutual heating)

Application of rule 310.60.(B)(1) will often avoid a costly up-rating of cables.


4- Conclusions• The 2011 National Electrical Code have a new article (Article

694) added that will provide rules to follow for safe wind turbine installation.

• However, this new Article only applies to wind turbine installations of 100 kW and less.

• The NEC is not covering the larger size wind turbines and wind power generation plants.

• Application of the NEC as is, by third parties in checking or approving WPP design as show in this discussion results, in some cases, in controversies.

• Many other articles may be found difficult to be applied to WPP. • There is need for an update of the NEC or a specific standard or

code for WPP


Questions and AnswersIntroduction


Logistics Presentations are available through AWEA Also available through our website

QUESTIONS are encouraged, but please hold until after each speaker finishes

Speakers will be available after panel for discussion

– http://grouper.ieee.org/groups/td/wind/

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Questions and AnswersPart 1


Questions and AnswersPart 2

Mitch Bradt, PE Univ. of Wisconsin-Madison · NESC- IEEE/ANSI-C2 National Electrical Safety Code....

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Transcript of Mitch Bradt, PE Univ. of Wisconsin-Madison · NESC- IEEE/ANSI-C2 National Electrical Safety Code....