Why do I need to do an Arc-Flash Analysis?

Transcription

1 Why do I need to do an Arc-Flash Analysis? Presented By Tom Norwood for Alexander Nizov, P.E. Principal/Manager Electrical Engineering Division TRAINING INSTITUTE, INC. A SUBSIDIARY OF MEGGER

2 Hazards Analysis Requirements OSHA (d) requires the employer to assess the workplace to: Determine if hazards are present or are likely to be present Determine required PPE for the hazards NFPA 70E requires electrical hazard analysis Shock Hazard Analysis Flash Hazard Analysis NESC, ANSI-C2 requires flash hazard analysis completed by January 1, 2009 Proposed revision to requires a flash hazard analysis NEC and CEC require hazard marking of electrical equipment

3 What happens in an Electrical Arc-Flash?

4 Electrical Arc-Flash As much as 80% of all electrical injuries are burns resulting from an arc-flash and ignition of flammable clothing Example of an arcing fault Over 2000 people are admitted into burn centers each year with severe electrical burns (2-6 6 months average stay)

5 If Clothing Ignites Clothed areas can be burned more severely than exposed skin Extensive 3 rd degree burns result

6 Electrical Arc-Flash Equal to 4 times the surface temperature of the sun (approximately 36,000 0 F) Vaporizes metals Ignites clothing Causes external burning of the skin Causes electrical blast (explosion) F (95 0 C) cell death (3 rd degree burn) 1.2 cal/cm 2 on-set of 2 nd degree burn

7 What is Electrical Arc-Flash? A rapid release of energy due to an arcing fault between a phase bus bar and another phase bus bar, neutral or ground Air is the conductor during an arc fault Limited to systems where bus voltage >240V Lower voltage levels normally will not sustain an arc

8 Key Arc-Flash Terms Arc-Flash Hazard: Dangerous electrical condition associated with the release of energy caused by arc- flash. Incident Energy: Amount of energy impressed on a surface, a certain distance away from the source, produced during an electric arc-flash. Note: Incident energy is measured in joules per centimeter squared (J/cm 2 ) or calories per centimeter squared (cal/cm 2 ). 1 cal = ~ 4.2 joules Flash Protection Boundary: An approach limit at a distance away from exposed energized parts which a person could receive a second degree curable burn due to an arc-flash event. Note: One cal/cm 2 (4.2 J/cm 2 ) is equivalent to the amount of energy produced by a cigarette lighter in one second!

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13 Electrical Arc Accident Didn t t think it could happen - but it did! Used a screwdriver to pry on live equipment 480-volt equipment, A-phaseA phase-to-ground (277- volt ground fault) Wasn t t wearing flash protection Wasn t t worth the risk He did fully recover He was LUCKY

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18 Electrical Arc-Blast - A Result of a High Energy Arc

19 Electrical Arc-Blast Copper vaporized by electrical arc expands 67,000 times (1 in. 3 copper = 1.44 yds. 3 vapor) Copper expanding - like dynamite Dynamite releases energy in microseconds Arc releases energy in milliseconds 1 MW = 1 stick of dynamite (1/3 lb of TNT)

20 Electrical Arc-Blast Arc - multi-hazard event Electrical Arc (temperature & incident energy) and Blast (explosion) Expansion produces explosion with: Molten metal Fragmented metal High temperatures Pressure on the body Doors and covers must be secure Body in safest position possible before operating electrical equipment

21 Electrical Hazards Safe work practices can minimize or eliminate the hazard (identified through analysis): Lockout/tagout w/temporary grounding Body positioning FR Clothing & PPE Insulated tools First choice is to minimize or eliminate the hazard Last choice is to use FR clothing and PPE

22 Electrical Safety should NEVER take a Holiday!

23 Job Assignment Perform preventive maintenance for food processing plant emergency power system. Perform work on a holiday weekend. Record data on performance of system.

24 Scope of Job Work to be performed on Memorial Day morning. Start work at 7:00 AM and finish at 11:00 AM. Open 15 kv switch to start emergency generator. Run generator for 3 hours under load to test reliability of system. Record ampere, water temperature, and oil pressure on generator.

25 Personnel Electrical supervisor, electrician, and technician. All workers had minimum of 5 years of experience. All workers had performed this type of work in the past.

26 Arc/Flash Video

27 Effect on Workers Two workers had 2 nd and 3 rd degree burns on 60% of their bodies. One of the workers was placed in a drug induced coma for over 60 days. The third worker had initial minor injuries. He has suffered long term effects, including neurological problems. Three families will never be the same again.

28 Post Evaluation No hazard analysis. When asked, the workers could not cite the three hazards of electricity in the workplace. Workers were not properly trained (qualified). Workers were wearing polyblend clothing. All three workers were within the flash protection boundary.

29 End Results Lost three long term employees OSHA citations and fines Negative publicity Litigation

30 Arc-Flash Hazard Analysis

31 What is Electrical Arc-Flash Hazard Analysis? Mathematical methods used to determine risk of personal injury as result of exposure to incident energy from arc flash

32 Typical Steps for Arc-Flash Hazard Analysis Presence of Electrical One-Line Diagram Collection of Required Field Component Data Power System Modeling (i.e., SKM, EDSA, ETAP) Power System Analysis: Short Circuit Study Protective Device Coordination Study Arc-Flash Hazard Analysis Written Reports

33 Collection of Required Field Component Data Utility Power Company available fault current at the entrance to the facility Arrangement of components on Electrical One-Line Diagram Nameplate of every electrical device Ratings and trip settings of every protective device Sizes, lengths and cross sections of all cables

34 Short-Circuit Study Electrical One-Line Diagrams must be created Maximum available fault current is calculated at each significant point in system Each interrupting protective device is analyzed to determine appropriate design and size in the event of bolted type short circuit Equipment must be reviewed for adequate size of bus bar to handle available fault current Bolted fault currents are converted into arc currents for additional analysis

35 Protective Device Coordination Study Examination of electrical system and available documentation with the goal of ensuring that over-current protective devices are properly designed and coordinated, rated, selected and adjusted so only the fault current protective device nearest the fault opens to isolate a faulted circuit from the system. Consists of time-current coordination curves that illustrate coordination among devices shown on one line diagrams.

36 Flash Hazard Analysis Magnitude of arc hazard determined by: NFPA 70E IEEE Standard 1584 Arc-flash hazard expressed in incident energy cal/cm 2 or J/cm 2 Arc-flash protective clothing is rated in: Arc Thermal Performance Value (ATPV) Incident energy (cal/cm 2 )

37 130.3 Flash Hazard Analysis Flash Protection Boundary Protective Clothing and Personal Protective Equipment for Application with a Flash Hazard Analysis < 600 volts 4 ft. (6 cycles x 50kA = 300kA cycles) > 600 volts 1.2 cal/cm 2 or ~ 5 J/cm 2 (threshold of a second degree burn)

38 Arc-Flash Warning Sign (Preferred) Required by NEC

39 Table 130.7(C)(9)(a) Hazard/Risk Category Classification Table Task (Assumes Equipment is Energized, and Work is Done Within the Flash Protection Boundary) Hazard/Risk Category V-rated Gloves Panelboards rated 240 V and below Notes 1 and 3 Circuit breaker (CB) or fused switch operation with covers on 0 N N CB or fused switch operation with covers off 0 N N Work on energized parts, including voltage testing 1 Y Y Remove / install CBs or fused switches 1 Y Y Removal of bolted covers (to expose bare, energized parts) 1 N N Opening hinged covers (to expose bare, energized parts) 0 N N Panelboards or Switchboards rated >240 V and up to 600 V (with molded case or insulated case circuit breakers) ñ Notes 1 and 3 CB or fused switch operation with covers on 0 N N CB or fused switch operation with covers off 1 N N Work on energized parts, including voltage testing 2* Y Y 600 V Class Motor Control Centers (MCCs) Notes 2 (except as indicated) and 3 CB or fused switch or starter operation with enclosure doors closed 0 N N Reading a panel meter while operating a meter switch 0 N N CB or fused switch or starter operation with enclosure doors open 1 N N Work on energized parts, including voltage testing 2* Y Y Work on control circuits with energized parts 120 V or below, exposed 0 Y Y V-rated Tools

40 Notes to Table 130.7(C)(9)(a) Note: V-rated Gloves are gloves rated and tested for the maximum line-to-line voltage upon which work will be done. V-rated Tools are tools rated and tested for the maximum line-to-line voltage upon which work will be done. 2* means that a double-layer switching hood and hearing protection are required for this task in addition to the other Hazard/Risk Category 2 requirements of Table 130.7(C)(10). Y = yes (required) N = no (not required) Notes: 1. Max. 25 ka short circuit current available, 0.03 second (2 cycle) fault clearing time.* 2. Max. 65 ka short circuit current available, 0.03 second (2 cycle) fault clearing time.* 3. For < 10 ka short circuit current available, the hazard/risk category required may be reduced by one number. 4. Max. 42 ka short circuit current available, 0.33 second (20 cycle) fault clearing time.* 5. Max. 35 ka short circuit current available, up to 0.5 second (30 cycle) fault clearing time.* 6. For < 25 ka short circuit current available, the hazard/risk category required may be reduced by one number. *Based on Tentative Interim Amendment (TIA)

41 Table 130.7(C)(11) Protective Clothing Characteristics

42 Rated Flash Protection (HR-2)

43 Rated Flash Suit (HR-4)

44 Conclusions The Arc-Flash Hazard Analysis is actually RISK MANAGEMENT.. There is basically three choices: 1. Be very conservative and require PPE HRC-4 4 in most cases resulting in higher cost. 2. Do nothing and suffer the consequences (pay later) 3. Perform the necessary AFHA and make adjustments to reduce the arc fault conditions resulting in reduced PPE requirements.

45 QUESTIONS & ANSWERS 52