Manitoba Hydro – Generation Operations Presented By: Allison Fritz, P. Eng. & David Hildebrand, P. Eng.

1. Introduction

2. Background

3. Generation Operations (GO) Arc Flash Program

4. Assessment Method and Calculations

5. Conclusion

Arc flash hazard poses a significant risk to electrical workers

It is the law in Manitoba that employers must protect workers from injury due to arc flash hazard

All workers at GO facilities are required to comply with the GO Arc Flash Hazard safety program

Important that all equipment and systems are designed to reduce the operational impacts of an arc flash hazard

There are generally three types of electrical hazards: i. Electrical shock ii. Arc blast iii. BURNS FROM ARC FLASH

An arc flash occurs when electrical current flows through the air and releases heat energy

Arc Flash Hazard is the total amount of heat energy exposed to a surface of the skin at a specified distance (measured in cal/cm2)

Arc flash events have a probability of occurring during interacting energized electrical equipment

An Arc Flash Hazard is identified as follows: ◦ Incident energy (cal/cm2)

◦ Working distance Distance from the arcing source to the face or torso

◦ Flash protection boundary Distance from the arcing source to where the incident

energy is 1.2 cal/cm2

Hazard Risk Category (HRC)

Hazard Risk Category (HRC)

Incident Energy

0 1.2 cal/cm2 1 4 cal/cm2 2 8 cal/cm2 3 25 cal/cm2 4 40 cal/cm2

Dangerous Greater than 40 cal/cm2

Each Hazard Risk Category (HRC) has a list of personal protective equipment (PPE)

Modified PPE if work is unsafe

For example, while working on equipment that is HRC 4 (40 cal/cm2) the following PPE must be worn: ◦ Arc-rated long-sleeve shirt and pants ◦ Arc-rated arc flash suit jacket and bib-overalls ◦ Arc Rated Hood (face shield & hard hat) ◦ Safety glasses ◦ Hearing protection ◦ Safety footwear ◦ Rubber insulating gloves (proper voltage class)

Manitoba Safe Work Bulletin No. 277 – Arc Flash Hazards, August 2011 ◦ “ The employer must ensure that an arc flash hazard

analysis is conducted for all electrical equipment to be worked on in an energized state, unless the following conditions are present: The circuit is rated 240 volts or less; The circuit is supplied by one transformer; and The transformer supplying the circuit is rated less than

125 kVA ◦ The findings of the arc flash hazard analysis must be

posted on the piece of equipment ”

CAN/ULC-S801-2014 – Standard On Electric Utility Workplace Electrical Safety for Generation, Transmission, and Distribution ◦ “8.1.1 When workers are required to work in proximity to

energized equipment above 50 V a.c., all potential sources of electric arc hazard shall be identified and risk assessed.”

CSA Z462-2015 – Workplace Electrical Safety ◦ Table 4A identifies tasks requiring PPE where arc flash risk is

significant

IEEE 1584-2002 – IEEE Guide for Performing Arc-Flash Hazard Calculations

IEEE Paper entitled “Arc Flash Calculations for Exposures to DC Systems” by D. R. Doan

The Generation Operations (GO) Arc Flash Working Group was initiated late 2014 to implement an arc flash safety program

Live work restriction directive was issued by the GO division management on April 21, 2015 (huge impact on operations)

GO Arc Flash Working Group was able to develop assessment methods and tools based on the industry standards

GO Arc Flash Safety Program is now successfully implemented and regular work has resumed

Information sharing via Sharepoint site

Arc Flash Safe Work Procedure

Generation Operations Technical Bulletin

Arc Flash Hazard Assessment eforms

Arc Flash Labels

Arc flash hazard labels are to be placed on each piece of equipment

Labels refer to the arc flash assessment via tracking number Labels indicate the worst-case hazard risk category, flash

protection boundary and working distance

Sample Label

Risk of arc flash hazard can be reduced at the design stage with the following methods: ◦ Reduced fault currents

◦ Faster/better coordinated protection systems

◦ Arc detection systems

◦ Barriered primary circuits

◦ Maintenance/troubleshooting with door closed

◦ Load-break/horsepower-rated safety switches

◦ Arc-resistant switchgear

◦ System redundancy

The risk of arc flash hazard can be reduced operationally with the following methods: ◦ DE-ENERGIZE!!! ◦ Identify flash protection boundary ◦ Wear appropriate arc-rated PPE ◦ Use temporary barriers & insulated tools ◦ Safe work procedures ◦ Worker training & awareness ◦ Use remote racking devices or insulated tools (ie. hot sticks)

Assessments are completed in two parts ◦ Energy Source Identification - Each exposed

electrical energy source in the work area must be identified and qualified, including the voltage, upstream protective device, source transformer, etc.

◦ Incident Energy Analysis – Each energy source must be analyzed to determine the maximum available incident energy that a worker would be exposed to if an arc flash event occurs. Two methods have been developed for incident energy analysis: Risk Based Assessments

Incident Energy Calculations

Incident Energy Analysis methods:

◦ Risk Based Assessments – for energy sources 240Vac and below, from sources less than 125kVA, Risk = Probability x Severity x Frequency

◦ Incident Energy Calculations – For energy sources above 240Vac or 125kVA, engineering calculations are performed to determine the incident energy.

PPE Requirements based on risk/quantified incident energy

IEEE 1584 Empirical Method ◦ 208 V – 15,000 V, 3-phase, AC

◦ Available short circuit current from 700 – 106,000 A

◦ Arc gaps of 13 – 152 mm

Lee Method (IEEE 1584, Section 5.4) ◦ Theoretical, applies to all AC voltages, short-circuit current, and arc gaps

◦ 1-phase; multiply by √3 for 3-phase

◦ In air; multiply by 3 for arc-in-a-box (enclosure)

Doan Method (CSA Z462, Appendix D) ◦ Theoretical, applies to all DC voltages, short-circuit current, and arc gaps

◦ Identical to Lee Method; only difference is due to rounding of unit conversion

Arc flash assessments are documented on electronic forms (eforms). The following are recorded on the eforms: ◦ Equipment designation ◦ Tracking number ◦ Each energy source & associated calculation/PPE

requirement ◦ Identification of the highest hazard risk category, flash

protection boundary and working distance ◦ Reference documentation ◦ Authentication from the person who prepared the

assessment

Assessment Tools: ◦ Breaker curve assessments ◦ Fuse curve assessments ◦ Minimum cable length assessments ◦ DC arc flash studies (most stations

completed to-date) ◦ AC arc flash studies (four stations

completed to-date) ◦ Equipment specific calculations

including system short-circuit study

Breaker curve assessments ◦ Example: Westinghouse, 100A, type BAB breaker, TCC curve shows HRC 3 for 600VAC

Fuse curve assessments ◦ Example: Ferraz-Shawmut, 200A, type A4J fuse, shows HRC 2 for 250VDC

DC arc flash studies ◦ Example – McArthur Falls Generating Station 250VDC System

AC arc flash studies ◦ Example – Gen 1 &

Gen 2 model from Pointe du Bois Generating Station Easy Power model

Background GO Arc Flash Program Assessment Methods & Calculations Conclusion & Key Points ◦ It is the law in Manitoba that employers must protect workers

from arc flash hazard.

◦ De-energize where practicable.

◦ Use risk reductions methods at design stage and operationally.

◦ Conduct hazard risk assessments, wear appropriate arc-rated PPE, establish flash protection boundary.

Possible Discussion Topics: ◦ Arc Flash Personal Protective Clothing ◦ Arc Flash Assessment Methods ◦ Arc Flash Calculations ◦ TCC curve Analysis

Questions? Thank you!