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Arc Flash Analysis - March 2004 ETAP 5.0 ETAP 5.0 Arc Flash Analysis

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Arc Flash Analysis - March 2004

ETAP 5.0ETAP 5.0

Arc Flash Analysis

Arch Flash Analysis OTI March 2004 – Slide 2

Electrical Arc Hazards

• Electrical Arcs can occur when a conductiveobject gets too close to a high-amp currentsource (energized conductor).

• Arc Flash Burns– The arc can heat the air to temperatures as

high as 35,000 F, and vaporize metal.

– Arc flash can cause severe skin burns by directheat exposure and by igniting clothing.

Arch Flash Analysis OTI March 2004 – Slide 3

Electrical Arc Hazards

• Arc Blast Impacts– The heating of the air and vaporization of metal

creates a pressure wave that can damagehearing and cause memory loss (fromconcussion) and other injuries. Flying metalparts are also a hazard.

• Falls– Electric shocks and arc blasts can cause falls,

especially from ladders or unguardedscaffolding.

Arch Flash Analysis OTI March 2004 – Slide 4

Definitions• Limited Approach Boundary: A shock protection

boundary not to be crossed by unqualified personsunless escorted by qualified personnel

• Restricted Approach Boundary: A shock protectionboundary to be crossed by only qualified persons.Shock protection is required.

• Prohibited Approach Boundary: A shock protectionboundary to be crossed by only qualified persons. Theuse of techniques that may require direct contact withenergized equipment.

Arch Flash Analysis OTI March 2004 – Slide 5

Definitions• Flash Protection Boundary: Distance at which the

incident energy equals 1.2 Cal/cm^2• Incident Energy: The amount of energy impressed on

a surface, a certain distance from the source,generated during and electrical arc event

• Working Distance: The dimension between thepossible arc point and the head and body of a workerpositioned in place to perform the task.

• Bolted fault current: A short-circuit contact betweentwo conductors at different potentials in which theimpedance between the conductors is zero.

Arch Flash Analysis OTI March 2004 – Slide 6

Definitions• Available fault current: The electrical current that can

be provided by the serving utility and facility-ownedelectrical generating devices and large electricalmotors considering the amount of impedance in thecurrent path

• Arcing fault current: A fault current flowing through anelectrical arc-plasma, also called arc fault current andarc current.

• Voltage (Nominal): A nominal value assigned to acircuit or system for the purpose of designating itsvoltage class (I.e. 120/240 V, 480Y/277 V, 600V, etc).

Arch Flash Analysis OTI March 2004 – Slide 7

Regulating Authorities

• OSHA 29 CFR 1910.132 (d) requiresemployers to access the workplace todetermine if hazards are present, or likely to bepresent and select and have each employeeuse the types of PPE that will protect them.

• OSHA 29 CFR 1910.333 Requires employeeswho are exposed to electrical shock hazard tobe qualified for the specific task that they areperforming and use the appropriate PPE

Arch Flash Analysis OTI March 2004 – Slide 8

Regulating Authorities• OSHA 29 CFR 1910.335 (a)(1)(I): Protective

equipment for specific body parts• OSHA 29 CFR 1910.335 (a)(2)(I): use of Insulated

tools when working around energized equipment.• NEC 110.6: equipment must be marked to warn

qualified persons of potential electrical arc-flashhazards.

• NFPA 70E-2000 Part II Chapter 2, paragraph 2-1.3.3states that arc-flash analysis must be performed inorder to determine the level of hazard and appropriatePPE for given tasks.

Arch Flash Analysis OTI March 2004 – Slide 9

IEEE 1584 2002 “Guide for Performing Arc FlashHazard Calculations”

NFPA 70E 2000 “Standard for Electrical SafetyRequirements for Employee Workplaces”

Protection From Arc Flash Hazards

Arch Flash Analysis OTI March 2004 – Slide 10

18 inches +18 inches +Working Distance

No LimitNo limitArc Duration Range

Open Air, Cubic Box,Cable Bus

Open Air,Cubic Box

Installations

Cal/cm2 or J/cm2Cal/cm2 or J/cm2Unit of Measure

0.7 kA to 106 kA16 kA – 50 kACurrent Range

208 – 15 kV (Empirical)

15 kV+ (Lee Method)208 V – 600 VVoltage Range

IEEE 1584-2002NFPA 70E-2000

Comparison of Arc Flash Standards

Arch Flash Analysis OTI March 2004 – Slide 11

Incident energy exposure at a working distance of 18”

for a 19.5 kA Arc @ 600 Volts (open air equipment)

600 Volt Arc in Open Air Incident energy Exposure @ 18 in.

0

5

10

15

20

0 10 20Fault clearing time (Cycles)

Cal

orie

/cm

^2

NFPA 70E-2000IEEE 1584-2002

Incident Energy Comparison

Arch Flash Analysis OTI March 2004 – Slide 12

600 Volt Arc in Closed Box Incident energy Exposure @ 18 in.

0

5

10

15

20

0 10 20Fault clearing time (Cycles)

Cal

orie

/cm

^2

NFPA 70E-2000IEEE 1584-2002

Incident energy exposure at a working distance of 18”

for a 19.5 kA Arc @ 600 Volts (enclosed equipment)

Arch Flash Analysis OTI March 2004 – Slide 13

NFPA Hazard Risk DeterminationQuick Table (Table 3-3.9.1 of 2000 Ed)

• Can you use them exclusively and still be incompliance for Arc-Flash safety?

• Developed based on outdated standard that onlycovers 600 V systems

• May result in unnecessary overprotection / underprotection

• Best when used only in emergency situation for quickevaluation of hazard level

• Standard mandates a detail arc-flash analysis beperformed when the task is not specifically covered bythis table

Arch Flash Analysis OTI March 2004 – Slide 14

General Steps for PerformingArc Flash Analysis

• Collect system information required for the ArcFlash Calculation

• Determine the system operating configuration

• Calculate 3-Phase bolted fault currents

• Calculate arcing fault current (IEEE only)

• Determine arc clearing time (arc duration) -TCC

Arch Flash Analysis OTI March 2004 – Slide 15

• Calculate Incident Energy

• Determine Flash Protection Boundary

• Determine Hazard/Risk Category based onNFPA 70E requirements

• Select appropriate protective equipment(PPE Matrix)

General Steps for PerformingArc Flash Analysis

Arch Flash Analysis OTI March 2004 – Slide 16

XXWorking Distance

XXOpen/Enclosed Equipment

XSystem Grounding(Grounded/Ungrounded)

XXCoordination Information (TCC)

XXSystem Nominal Voltage

XGap Between Conductors

XDistance X Factor

IEEE1584

NFPA70ERequired Parameter

Data Collection for Arc Flash

Arch Flash Analysis OTI March 2004 – Slide 17

Gap between Conductors

Arch Flash Analysis OTI March 2004 – Slide 18

Additional Considerations

• Up to date one-line-diagrams

• Data similar to information required for Short-circuit studies like MVAsc values of Utilitiyincluding X/R, subtransient and transientreactance, cable impedance, etc.

• Include low voltage equipment which is oftennot included in large systems

Arch Flash Analysis OTI March 2004 – Slide 19

3-Phase Bolted Fault Current• Perform ANSI/IEC short circuit study that considers

the following:– 3-phase bolted fault– ½ cycle or 1½-4 cycle fault current depending on the

type of device or system voltage– Include all cables & Overload heaters– Prefault voltage (nominal circuit voltage)– Short-circuit Calculation should be more accurate rather

than too conservative (faults may persist longer at lowercurrent levels which may translate into higher energy)

Arch Flash Analysis OTI March 2004 – Slide 20

System Modes of Operation• Open or looped• One or more utility feeders in service• Utility interface substation secondary bus tie breaker

open or closed• Unit substation with one or two primary feeders• Unit Substation with two transformers with secondary

tie opened or closed• MCC with one or two feeders, one or both energized.• Generators running in parallel with the utility supply or

in standby mode

Arch Flash Analysis OTI March 2004 – Slide 21

Why use 3-Phase Faults

• Line to Line faults quickly escalate into three- phasefaults

• LV L-G faults in solidly grounded systems quicklyescalate into three phase faults

• LV L-G faults in Ungrounded / High resistancegrounded systems do not release enough energy.

• MV faults in low resistance or reactance groundedsystems should be cleared quickly, but worst casescenario 3-phase fault should be considered

Arch Flash Analysis OTI March 2004 – Slide 22

Standards for Short-Circuit

• IEEE Std 141-1993 (IEEE Red Book)

• IEEE Std 242-2001 (IEEE Buff Book)

• ANSI (different standards like C37, etc)

• IEC (60909, 60363, etc)

• See ETAP help file for more standards

Arch Flash Analysis OTI March 2004 – Slide 23

))(lg(**00304.0))(lg(**5588.0

*000526.0*0966.0)lg(*662.0)lg(

bfbf

bf

IGIVGVIKIa

−+

+++=

For buses with nominal kV in the range of 0.208 to 1.0 kV:

In general, arcing current in systems below 15.0 kV will be lessthan the 3-phase fault current because of arc impedance.

Arcing Current

Arch Flash Analysis OTI March 2004 – Slide 24

For buses with nominal kV rating greater than 15 kV, thearcing current can be considered to be the same as thebolted fault current:

For buses with nominal kV rating in the range of 1 to 15.0 kV:

)Ilg(*983.000402.0)Ialg( bf+=

bfIIa =

Arcing Current

Arch Flash Analysis OTI March 2004 – Slide 25

Arc Duration LV CB

Arch Flash Analysis OTI March 2004 – Slide 26

Arc Duration LV CB

Arch Flash Analysis OTI March 2004 – Slide 27

Arc Duration for Fuses

Arch Flash Analysis OTI March 2004 – Slide 28

Incident Energy

Empirical method (1.0 to 15.0 kV)

= x

x

nf DtECE 610*2.0

**184.4

Lee method (higher than 15.0 kV)

= 2

6 **10*142.2DtIVE bf

Arch Flash Analysis OTI March 2004 – Slide 29

Flash Protection Boundary

Empirical method (1.0 to 15.0 kV)

= x

x

nf DtEC 610*2.0

**184.42.1

Lee method (higher than 15.0 kV)

= 2

6 **10*142.22.1DtIV bf

Arch Flash Analysis OTI March 2004 – Slide 30

9 – 1228 > cal/cm2 ≥ 5

4.5 – 815 > cal/cm2 ≥ 1.24.5 – 701.2 > cal/cm2 ≥ 0

24-304cal/cm2 ≥ 2516-20325> cal/cm2 ≥ 8

Total WeightOz/yd2

Hazard RiskCategory

Incident EnergyExposure cal/cm2

Hazard / Risk CategoriesNFPA 70E 2000

Arch Flash Analysis OTI March 2004 – Slide 31

Categories 0 and 1 Personal Clothing/Equipment Requirementsper Table 3-3.9.2 of NFPA 70E 2000

Personal Protective EquipmentPPE Matrix

Arch Flash Analysis OTI March 2004 – Slide 32

Category 0 (up to 1.2 Cal/cm2)

• Shirt (Long-Sleeve)

• Pants (Long)

• Safety Glasses

• V-Rated Gloves

• Insulated Tools

Arch Flash Analysis OTI March 2004 – Slide 33

Category 1 (1.2 up to 5.0 Cal/cm2)

• Shirt (Long-Sleeve) FR

• Pants (Long) FR

• Safety Glasses FR

• V-Rated Gloves

• Insulated Tools

• Hard Hat FR

Arch Flash Analysis OTI March 2004 – Slide 34

Category 2 (5.0 up to 8.0 Cal/cm2)

• Category 1 Requirements

plus

• Extra Layer of UntreatedNatural fiber (Shirt &Pants)

• Leather Work Shoes

FR FR

Arch Flash Analysis OTI March 2004 – Slide 35

Category 3 (8 up to 25 Cal/cm2)

• Category 2 Requirements

plus

• Coveralls up to 2 Sets

• Double Layer SwitchingHood

• Hearing Protection

Arch Flash Analysis OTI March 2004 – Slide 36

Category 4 (higher than 25 Cal/cm2)

• Category 3 Requirements

plus

• Flash Suit

Arch Flash Analysis OTI March 2004 – Slide 37

PPE Incident Energy Rating

• ATPV: is the defined as the incident energy on a fabric ormaterial that results in sufficient heat transfer through thefabric or material to cause the onset of a second degreeburn.

• EBT: is defined as the average of the five highest incidentenergy exposures values below the Stoll curve where thespecimens do not exhibit breakopen. EBT is reported whenthe ATPV cannot be determined due to FR fabricbreakopen.

• HAF%: is the heat transfer capability of the fabric ormaterial

Arch Flash Analysis OTI March 2004 – Slide 38

Stoll Curve

Arch Flash Analysis OTI March 2004 – Slide 39

FR Equipment Layering

Arch Flash Analysis OTI March 2004 – Slide 40

Example of Layered System

100%)100(*' )/( 2

HAFEE cmcalcalculated

−=

• Proposed PPE for Arc Fault with E = 22 Cal/cm^2

ProposedEquipment

ATPV Rating(cal/cm^2)

EBT(cal/cm^2)

HAF %

FR Shirt (longSleeve)

5 9 85

FR Raincoat 10 18 70

Arch Flash Analysis OTI March 2004 – Slide 41

Example of Layered System

• Energy that passes to second layer is higher than ATPV

• EBT is too low for outer layer (possible breakopen)

ModifiedEquipment

ATPV Rating(cal/cm^2)

EBT(cal/cm^2)

HAF %

FR Shirt (longSleeve)

9 9 85

FR Raincoat 15 22 70

2/6.6100

)70100(*22' cmcalE =−=

Arch Flash Analysis OTI March 2004 – Slide 42

Considerations for layering

• ATPV rating of the equipment must be abovethe calculated incident energy of the Arc forsingle layer FR system

• In multiple layer FR system there must be nobreakopen that reaches the innermost layer toprevent possible ignition of such

• NFPA example recommends

Arch Flash Analysis OTI March 2004 – Slide 43

Arc Fault atLocation B

Arc Fault atLocation A

Example1

Arch Flash Analysis OTI March 2004 – Slide 44

Arch Flash Analysis OTI March 2004 – Slide 45

Example1

• Fault at location B

Calculated incident energy = 0.784 Cal/cm2

(Relay B operates at 1.206 cycles + 5 cycles HVCB)

• For a fault at location A

Calculated incident energy = 0.945 Cal/cm2

(Relay A operates at 2.406 cycles + 5 cycles HVCB)

• Hence the Incident Energy to be considered for this systemshould be 0.945 Cal/cm2 (the most conservative value).

Arch Flash Analysis OTI March 2004 – Slide 46

Arc Fault atLocation C

Example 2

Arc Fault atLocation D

Arch Flash Analysis OTI March 2004 – Slide 47

Arch Flash Analysis OTI March 2004 – Slide 48

Example 2

• Fault at location C:

Calculated incident energy = 7.604 Cal/cm2

(LVCB 15 operates in 0.150 sec.)

• For a fault at location D:

Calculated incident energy = 5.576 Cal/cm2

(LVCB 16, 17 & 18 operate in 0.115 sec.)

• Hence the Incident Energy to be considered for this systemshould be 7.604 Cal/cm2 (the most conservative value).

Arch Flash Analysis OTI March 2004 – Slide 49

Arc Flash Hazard Labels

• Place labels at each location (cubicle)

• Contain information that is clear andcommunicates the danger level

• Meet current format per ANSI Z535 2002(safety symbols)

Arch Flash Analysis OTI March 2004 – Slide 50

Examples of Safety Labels

Arch Flash Analysis OTI March 2004 – Slide 51

Arch Flash Analysis OTI March 2004 – Slide 52

Arch Flash Analysis OTI March 2004 – Slide 53

26.5 kV < Bus kV ≤ 36.0 kV436000

17.0 kV < Bus kV ≤ 26.5 kV326500

7.5 kV < Bus kV ≤ 17.0 kV217000

1.0 kV < Bus kV ≤ 7.5 kV17500

High Voltage Gloves

0.500 kV < Bus kV ≤ 1.0 kV01000

kV ≤ 0.500 Bus kV ≤≥00500

Low Voltage Gloves

Bus nominal kV rangeClassMax. use voltage AC

(L-L) (V-Ratingfield)

Types of Insulating Glove

ASTM Insulating Glove Voltage Classes