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Arc Flash

Conrad St.Pierre

Arc-Flash Hazard Evaluation Provides Safer and More

Efficient Workplace

Requirements of 2003 NEC• Article 110.16 states ‘Flash protection is required when

examining, adjusting, servicing, or maintaining energized equipment. The equipment shall be field marked to warn qualified persons of potential electric arc flash hazards’ ‘Flash protection is required when examining, adjusting, servicing, or maintaining energized equipment. The equipment shall be field marked to warn qualified persons of potential electric arc flash hazards’

• NEC is generally not retro-active, but for safety reasons should apply to all to all electrically equipment.

Dupont Nameplate

NFPA 70E

“Flash hazard analysis shall be done before a person approaches any exposed electrical conductor or circuit part that has not been placed in an electrically safe work condition.

The flash hazard analysis shall determine the flash protection boundary and the personal protective equipment that people within the arc flash boundary must use.”

Clothing RequiredMin. PPE Rating

Range of Calculated incident energy

Flash Hazard Risk Category

Cotton underclothing plus FR shirt, pants, plus multi-layer switching suit or equivalent

100 cal/cm240+ to 100 cal/cm25

Cotton underclothing plus FR shirt, pants, plus double layer switching coat and pants

40 cal/cm225+ to 40 cal/cm24

Cotton underclothing plus FR shirt, pants, overalls or equivalent

25 cal/cm28+ to 25 cal/cm23

Cotton underclothing plus FR shirt and pants

8 cal/cm25+ to 8 cal/cm22

FR shirt and pants5 cal/cm21.2+ to 5 cal/cm21

4.5-14.0 oz/yd2 untreated cottonN/A0 to 1.2 cal/cm20

Minimum Thermal Recommended Protection(Based on proposed updates to NFPA 70E)

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An arc flash can be ExpensiveRecovery and rehabilitation costs can be staggering

• Cost for an incident involving one fatalityand two injured employees has exceeded$12 million.

• Another company’s expenses for three serious incidents in a three year periodhave exceeded $875,000.

Reality of Arc Flash HazardArc current creates: – A brilliant flash of light– A loud noise– Intense heat– Fast moving pressure wave

Products of arcing fault are:– Ionized gases– Metal vapors– Molten metal droplets– Shrapnel

Development of Arc Flash Calculations

• In 1982 Ralph Lee presented an IEEE paperon Arc Flash Hazard

• NFPA 70E – 2000 Recommended Arc Flash Calcs

• IEEE-1584-2002 - Published Calc Methods

• IEEE 1584 Standard refers to Lee’s work as Lee’s Method.

• Equation use VLL and Ibolted fault and givesworking distance

Vs

Source

Zs

Arc Volts

Zcable

One Line Diagram

What is in IEEE 1584?

• Results based on tests

• Arc Flash in Open Space, on Cables, MV Swgr, LV Swgr, MCC, Dist. Panels

• Voltages 208 to 1000V, 1000 to 5000V5000-15000-V, >15-kV>15-kV uses Lee’s Method

• Grounded and Ungrounded Systems

• Faults cleared by CLF Equations

Video 1

3

Video 2Results of Experiments

• Best fit for arcing current: equations with terms of • bolted fault current• voltage• gap between conductors• open air or box

• Best fit for incident energy: equations with terms• arcing current• gap between conductors • open air or box• grounded or ungrounded

Getting from Incident Energy to PPE

• Utilizing PPE with Cal/cm2 values of 1.2, 4, 8, 25, 40 the IEEE Equations resulted in adequate levels of PPE in 95% of the arc-flash tests

• In 5% of the tests, the PPE chosen was one level too low

Arc CurrentLV Ia = 10 [K + 0.662 log(Ib) + 0.0966 V

+ 0.000526 G + 0.5588 log(Ib) V – 0.00304 log(Ib) G]

MV Ia = 10 [0.00402 +0.983 log (Ibf)]where:

Ia = arcing current (kA)K = – 0.153 for open configuration

or – 0.097 for box configurationlog(Ib) = log10 of sym RMS bolted fault current (kA)Voltage = system voltage (kV)G = distance between buses (mm)

LV Equation - Incident Energy Normalized

En =10 K1 + K2 + 1.081 log(Ia) + 0.0011 G

whereEn = incident energy normalized to

0.2 seconds and 610 mm distanceK1 = -0.792 for open configurations

or -0.555 for box configurations K2 = 0 for ungrounded and high resistance

grounded systems,or -0.113 for grounded systems

G = bus bar spacing or gap (mm)

Incident Energy

E = Cf 10 log(En)(t /0.2)( 610X / DX)

whereE is incident energy in cal/cm2

Cf is calculation factor of 1.0 for Voltage > 1kV,or 1.5 for Voltage < 1kV

t is time in secondsD is working distance in mmX is the distance exponent from table based on

enclosure size and voltage

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Man without

PPEProtection

Human ConductorCausing

Arc

Racking Out Breaker• Grounded Definition• Incident Energy verses Voltage and Test Data

0 – 1000V have voltage term in equation

1000+ to 15000 V do not have voltage term in equation. Two grouping 1-5-kV, 5-15-kV

15000 V+ has voltage in equation

Questionable Items

Standard K2 = 0 for ungnded and hi-resistance gnded systemsK2 = –0.113 for grounded systems

SpreadsheetUngded, Res Gnding, Other Imp gnded K2 = 0Solid Grounded K2 = -0.113

-0.113-0.113Solid0.0-0.113Low Imp0.00.0Hi-Imp0.00.0UnGnd

SpreadsheetStandardGrounding

Grounded Definition

600-V

480-V

13.8-kV

2.4-kV

4.16-kV

13.8-kV

34.5-kV

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

Inci

dent

Ene

rgy

(Cal

/cm

^2)

0 10 20 30 40 50 60

Bolt Fault Current in kA

0

25

50

75

100

125

150

175

200

Inci

dent

Ene

rgy

(Cal

/cm

^2)

0 10 20 30 40 50 60

Bolted Fault Current in kA

Time = 0.1 sec, Working distance = 24 inches, Arc gap per IEEE 1584 for switchgea, Grounded

*

Incident Energy verses Bolted Fault Currentfrom IEEE 1584 Equation

5

2

0 10 20 30 40 50 60 70 80Bolted kA

0

10

20

30

40

50

60

Cal

/cm

IEEE Lee's Method

IEEE 1584 Equations

Test Data Points

Comparison of IEEE Equations to 600 Volt Open Air Arc Test DataIEEE 1584 Eq, based on 24 inch to subject, 1.25 Inch Arc Gap, 1.0 sec

Incident Energy verses Voltage and Test Data

IEEE Lee's Method

IEEE 1584 Equations

Test Data Points

0 10 20 30 40 50 60Bolted kA

0

50

100

150

200

250

300

Cal

/cm

2

Comparison of IEEE Equations to 4160 Volt Open Air Arc Test DataIEEE 1584 Eq, based on 24 inch to subject, 4.0 Inch Arc Gap, 1.0 sec

Incident Energy verses Voltage and Test Data2

IEEE 1584 Equations

Test Data Points

IEEE Lee's Method

0

100

200

300

400

500

Cal

/cm

0 10 20 30 40 50 60Bolted kA

IEEE 1584 Eq, based on 24 inch to subject, 6.0 Inch Arc Gap, 1.0 sec

Comparison of IEEE Equations to 13,800 Volt Open Air Arc Test

Incident Energy verses Voltage and Test Data

MCC or PANELBOARD

LV SWITCHGEAR

SMALL

LARGE

BOX APPLICATION

165x165 cm

254x254 cm

OPENING

191 cm

508 cm

DEEP

38 cm

10 cm

ELECTRODEELECTRODE

SMALL BOX

LARGE BOX

Test Cubicles (Box)

Arc Pressure

• In 1987 Ralph Lee presented an IEEE paperon Arc Pressure

• Arc Pressure = 11.5*kA lbs/ft2(Distance. from arc in feet)0.9

• for 50-kA fault at 2 feet = 308 lb/ft2

Video 3

6

1. Low voltage remote trip and close

2. Use a remote or longer operating arms when racking in or opening/closing breakers

3. Place a shield between the technician and the device being placed in service or racked in

4. Review protective devices to see if they canbe lowered in time and pick-up.

Limiting Flash Hazard

5. On double ended load centers with normally closed tie, open an incoming breaker or th tie breaker

6. Determine if smaller fuses can be used

7. Change relay settings when working onequipment

Limiting Flash Hazard

Hi-impact plastic shield with arm holds

Breaker

Switchgear Cubicle

Protective Shield

Breaker

Relay withInst. Set

Switchgear Bus

Feeder

CT

Safety On/Off

Time OvercurrentRelay Trip Contact

O/CO/C CT

Relay withInst. Set

Breaker Main

FeederBreaker

To - DC busTo Main BreakerTrip Circuit

Lt Inst. OvercurrentTrip Contact

Switch

Relay without Inst. SetCT O/C

Main Breaker Control Circuit + DC Bus

Circuit to Reduce Arc Fault Time

Arc Heat

53 51 3 5 10 100 3 5 1000 3

10

50

100

1000

500300

30

53

1

.5

.3

.1

.05

.03

.01

SECONDS

101 3 5 100 3 5 33 5 51000

.01

.03

.05

.3

.5

3

.1

1

5

10

30

50

1000

300500

100

SECONDS

CURRENT IN AMPS X 100 @ 480 VOLTS

ARC-1 FDRGeneral Electric RMS-9Low Voltage PowerSensor = 800 Plug = 600Curr Set = 1.0 Trip = 600LTBand = 1 Inst = 10.0STpu = 4.0 I^2t = IN Bd = Min

250E

1600A

600A

480V

4160V

1000 kVA

MainGeneral Electric RMS-9Low Voltage PowerSensor = 1600 Plug = 1600Curr Set = 1.0 Trip = 1600LTBand = 1 Inst = NoneSTpu = 2.0 I^2t = IN Bd = Min

Transf Amps

85% Transf Amps

1000 kVAS&CSMU-40 4.8 KVStd Speed250E SF= 1

17.6

1.2

5.3

8.8

1.4

4.4

Cal/Cm^2

17.3 0.42

1.014.3Fuse

0.0519.7Feeder

0.3014.3Main

85% fault

Fuse

0.0523.2Feeder

0.2117.3Main

Time(sec)

kALocation

100% Fault

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Slide the tab to run Short Circuit.

W A R N IN GW A R N IN GA p p ro p r ia te P P E R e q u ire d

V o lts M ax S h o rt C ircu it k A

R eq u ire d XN o t R e q u ire d

B u s E le c tr ic a l S h o c k a nd F la s h H a z a rd

5 .04 80 0

E q u ip m en t N a m e: 01P ro jec t: T 12 3

A rc F la s h b o u n d a ry a t e n e rg y < 1 .2 c a l/c m ^ 2

W h e n L iv e P a r ts a re E x p o s e d (R e s t r ic te d S h o c k H a za r d D is ta n c e = 2 6 in c h )

C lo th in gL e v e l 0 F a c e

S h ie ld X

G lo v eC la s s 0 E y e

P ro te c tio nX

In s u la te dT o o ls X H a ir /B e a rd N e t

N o t A llo w e d X

P P E B as ed o n 1 7 .9 in c h W o rkin g D is tan c eA rc F las h b ou n d ary , P P E re q u ire d w i th in 1 3 .2 in c h es )

Warning Label Plot of Incident Energy