NHP Arc Flash Presentation

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13/11/2014

ARC FLASH HAZARD
AWARENESS & MITIGATION
by
Sesha Prasad
NHP engSPACE
Melbourne
th
12 November 2014

OVERVIEW OF TOPICS









Introduction to Arc Flash Hazards
Brief Overview of Australian Arc Flash Standards
Arc Flash PPE Specs – NFPA 70E
Arc Flash Hazards in Modern Power Systems
Arc Flash Incident – A Case Study
Mitigation of Arc Flash Hazards
Arc Flash Analysis – Case Study Demo
Conclusions & Questions
2

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13/11/2014

ARC FLASH HAZARD
• Arc temp can reach up to about 20,000oC
(4 times the temperature on sun’s surface!)
(Fires in Petrochemical industries ≈ 2,800oC)







Arc plasma temperatures are > 5,000oC
Gaseous copper is 44,000 times solid metal
Severe or even fatal burns
Clothing can be ignited several meters away
Physical injuries due to arc blast
3

ARC FLASH IN 415V BOARD

4

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13/11/2014

ARC FLASH IN 415V BOARD

5

CAUSES OF ARC FLASH
• We are more concerned with an arc flash
incident when a person is working near
energised conductors
• Accidental contact
• Dropped Tools
• Faulty / Inappropriate Test Equipment
• Misalignment of contacts or parts
• Carless device removal / operation
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13/11/2014

CASE STUDIES – IEEE 1584
• IEEE 1584 documents a total of 49
incidences
• 24 incidences are at <1kV (480V)
• 10 incidences from 1kV to 6.6kV
• 8 incidences from 6.6kV to 15kV
• 7 incidences >15kV
7

CASE STUDIES – IEEE 1584
• Electrician was installing a fuse in a panel
• An electrical connector touched brace bar while
racking in
• Trouble shooting with a voltmeter when the
meter was shorted (several incidences)
• Two electricians were taking current readings
with a clamp on type ammeter
• Electrician was testing for voltage using a HV
probe inside a breaker compartment
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13/11/2014

CASE STUDIES – IEEE 1584
• Ground wire touched the energised phase lug while
moving ground wire inside a panel
• Trip button fell on bus while trouble shooting trip button
• Screw penetrated phase conductor while installing MCCB
• The wrench being used by the electrician bridged two
phases of a 13.2kV circuit breaker
• Electrician was working on 12kV breaker controls without
insulating barriers
• Three employees were removing a wrong breaker which
was energised
9

ARC FLASH HISTORY
• Ralph Lee – 1982 – ‘The Other Electrical Hazard’
• NFPA (Nat Fire Prot Assoc in US) Statistics – 1994
• 1 to 2 fatality due to shock & arc flash burns per day
• 5 serious burn injuries per day






Doughty, Neil & Floyd Equations – 1998 – Up to 600V
NFPA 70E – 2000 – PPE Table & Doughty’s Eqn
IEEE 1584 – 2002 - Up to 15 kV / Arc Flash Current
NFPA 70E 2004 / 2009 / 2012 / 2015
10

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13/11/2014

DOUGHTY (NFPA) EQUATION

11

AUST STANDARDS
• ESAA – NENS 09:2004 / ENA NENS 09:2006
– National Guidelines for Selection, Use and
Maintenance of PPE for Electrical Hazards
– Applicable for Electric Utilities
– Equation is based on single phase faults
– 3-Ph Heat Flux = 3 x 1-Ph Heat Flux
– Cotton drill clothing of varying thickness/layers
– Cotton can catch fire under arcing conditions !
– 185gsm cotton clothing for 10cal/cm2 !
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13/11/2014

AUST STANDARDS
• AS 4836 : 2011
– Safe Working on or near LV Installations
– Included arc flash PPE specs in 2011 edition





Face Shield rated at 10 cal/cm2
Arc Flash suit rated at 40 cal/cm2
Flame Resistant Gloves and Protective Clothing
Cal/cm2 ratings not specified for Gloves and Clothing

– Provides a table of PPE specs for Isolated Work,
Switching/Isolation, Testing/Fault Finding and Live
Electrical Work for various Switchboard Ratings
13

AUST STANDARDS
• AS 4836 – Testing / Fault Finding
– PPE specs is based on Switchboard Rating
• Up to 100A – No need for Arc Flash PPE
• 100 – 400A – Face Shield / Arc Flash Suit (if required)
• 400 – 1000A – Face Shield necessary, AF Suit (if reqd)

– Arc Flash Incident Energy is mainly determined by
Fault Current, Arc Duration and Working Dist
– Use of AS 4836 results in false sense of security
and exposes electrician to dangerous conditions
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13/11/2014

AUST STANDARDS
• AS 3007 : 2013
– Electrical Equipment in Mines and Quarries
• Design shall include provisions for prevention of arc
flash / arc blast injury (Refer to AS 3439 / AS 3000)
• Consideration must be given to remote switching
• Clearly define arc flash levels and PPE required
• For information on arc flash / arc blast protection,
refer to IEEE 1584 and NFPA 70E

15

PPE SPECS – NFPA 70E - 2004

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13/11/2014

NFPA 70E-2004 - ISSUES







PPE 3 & 4 – are not comfortable
Cotton underwear– Conventional short sleeve & brief/shorts
Flame Retardant (FR) is not Arc Resistant (AR)
Why specify number of layers?
PPE specification in cal/cm2 – not layers
PPE Table does not include face, hand and leg
protection
17

PPE SPECS – NFPA 70E - 2012

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13/11/2014

PPE SPECS – NFPA 70E - 2012

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PPE SPECS – NFPA 70E - 2012





NFPA 70E-2012 Specs are simple & clear
Specifies clothing & other PPE in same Table
No of layers is no longer mandatory
Face shields come with added conditions
Arc flash suit hood is the preferred option
• Arc rated leather gloves only for cat 3 & 4
• Leather work shoes for all categories
20

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13/11/2014

SIMPLIFIED PPE TABLE
• Note that Cat 1&2 and Cat 3&4 have
effectively same specifications – except for
incident energy specs
• NFPA 70E – 2012 provides an alternative PPE
table in Appendix H
• This is the relevant table when arc flash
analysis is done
21

SIMPLIFIED PPE TABLE

22

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13/11/2014

EVERY DAY WORK WEAR ?

12 Cal / cm2 PPE

23

WHY 4 CATEGORY TABLE ?
• 4 category is now relevant only for the ‘Work
Based’ table provided in NFPA 70E
• This table has been made much simpler in
NFPA 70E – 2015 edition
• This is now the mandatory part of NFPA 70E
• Arc flash analysis is now optional, however,
this provides for simplified PPE specs
24

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13/11/2014

NFPA 70E – 2012 WORK TABLE

25

ARC FLASH HAZARD IN
MODERN POWER SYSTEMS
• Let us consider 415V switch board supplied by a
11kV/415V 250kVA transformer
• 7kA Fault Level ; Trip Time 0.1s ; Dist 500mm
• Incident Energy = 1.3 cal/cm2
• Can get away with normal cotton clothing
• What if the Transformer rating is higher?
• Same 415V switchboard can now become very
“Dangerous” !
26

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13/11/2014

ARC FLASH HAZARD IN
MODERN POWER SYSTEMS

27

ARC FLASH – CASE STUDY
• Arc Flash 480V, 17kA (750kVA?), 0.85s

28

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13/11/2014

ARC FLASH - CASE STUDY (ESV)
• 415V Switchboard in club house of a retirement
village
• Electrician was replacing an RCD
• Shorts, T-shirt, Synthetic jacket & Hi Vis vest
• Adjusting a live bus with screw driver
• 750kVA txf min – Typical pad mount ?
• Trip Time > 1s ?
• Inc En > 30 cal/cm2 ?
29

ARC FLASH - CASE STUDY

30

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13/11/2014

ARC FLASH – A CASE STUDY







Burns to face, abdomen, hands and legs
Shorts, T-shirt, synthetic jacket & Hi Vis vest
Jacket & Hi Vis Vest melted
3 days in coma & 4 wks in specialist hospital
6 weeks of rehab and more operations
Unable to go in sun without being covered
up for the foreseeable future
31

HAZARD MITIGATION
• Electrician awareness – especially at LV boards
• Most arc flash incidents are due to inadvertent
contact
• Use appropriately designed equipment and tools, to
avoid possible contact with energised conductors
• Use 8 or 12 cal/cm2 clothing as a minimum
• Comfortable arc rated clothing is available now
• Use arc rated face shield as a part electrical work
• Comfortable combination helmet / face shield is
now available
32

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13/11/2014

HAZARD MITIGATION
• Ensure fast clearance for arc flash currents
(30 to 60% of bolted fault currents)
• Conduct arc flash studies to establish arc
flash energy levels at switchboards
• More stringent checks on O/C prot settings
• Relays with two groups of protection
settings are now available – Use them
• Arc flash relays for high fault level boards
33

CONCLUSIONS
• Be Aware of Arc Flash Hazard
• 415V Switchboards with high fault currents are
Dangerous
• Trip Arc Flash Current Quickly - not just Bolted
Fault Current
• Use Arc Rated PPE
• Thank You
34

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