Hilton Hotel and Royale Palms
Myrtle Beach, South Carolina
July 11, 2011
Michael C. Dougherty, PE
A.J. Molnar, PE
Southeastern Consulting Engineers, Inc.
Charlotte, NC
What is Arc Flash?

Definitions
 Per the National Fire Protection Association
(NFPA):
○ Arc – “Occurs when an insulating medium such as air
is breached by a conducting component.”
○ Arc Flash – “The energy released during an arcing
fault”. This occurs when current flows through a
medium that is not intended to conduct electrical
current. Because the arc current is not intended, the
arc current releases energy that also is not intended,
thus exposing a worker to unexpected hazards.
What is Arc Flash?

Definitions (continued)
○ Arc Flash Hazard - “a dangerous condition
associated with the release of energy caused by an
electric arc.”
○ Flash Hazard Analysis – A study investigating a
worker’s potential exposure to arc-flash energy,
conducted for the purpose of injury prevention and
the determination of safe work practices and the
appropriate levels of Personal Protective Equipment
(PPE).”
ARC FLASH EXAMPLE
ARC FLASH EXAMPLE
Types of Electric Faults

Bolted Fault - solidly connected fault path

Arcing Fault – current flows through ionized air
Arcing faults release most of the energy of the
fault out into the surrounding environment.
Bolted faults most of the energy flows through
the faulted equipment.
Arc Flash Facts



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

An arc flash is a source of intense heat, light,
sound, and pressure.
Arc temperature can reach 35,000˚F – this is
four times hotter than the surface of the sun.
Fatal burns can occur at distances over 10 ft.
Five to ten Arc Flash explosions occur in electric
equipment every day in the United States.
Over 2000 people per year are treated for
severe burns from electrical arcs.
As much as 80% of all electrical injuries are
burns resulting from an arc-flash and/or the
ignition of flammable clothing.
Personnel Hazards
 Direct injury
 Pressure wave
 Contact with energized parts
 Radiation burns from intense heat & light
 Indirect injury
 Shrapnel from component parts - the blast can
hurl shrapnel at velocities over 700mph.
 Molten Copper and Steel
 Breathing superheated air & arc by-products
Potential Causes of Arc Flash
 An arc flash can be caused a number of
ways, including:






Tracking across insulation surfaces
Accidental contact with energized parts
Inadequate short circuit ratings
Tools dropped on energized parts
Wiring errors and loose connections
Contamination, such as dust on insulating
surfaces
 Corrosion of equipment parts and contacts
 Improper work procedures
 Equipment failures
 Animals
Interrupting 500kV with Air
Break Switch
Industry Standards and Regulations
used to protect workers from Arc Flash
 NEC 2008
 OSHA 29 CFR 1910
 NFPA 70E - 2009
 IEEE 1584
 National Electrical Safety Code®
(NESC) - 2007
2007 NESC Article 410.A.3

“Effective as of January 1, 2009, employers are
to ensure that an assessment is performed to
determine potential exposure to an electric arc
for employees who work on or near energized
parts or equipment. If the assessment
determines a potential employee exposure
greater than 2 cal/cm2 exists, the employer
shall require employees to wear clothing or a
clothing system that has an effective arc rating
not less than the anticipated level of arc
energy.”

How do you comply with NESC 410.A.3?
 Utilities must perform an assessment of their entire
electric system and verify that their PPE is providing
adequate protection.
 The assessment utilizes voltage, clearing time and fault
current to determine the available incident energy.
 You can determine this by using NESC tables 410-1 and
410-2 or by performing an arc flash hazard analysis.
○ When an arc hazard analysis is performed, it shall include a
calculation of the estimated arc energy based on the available
fault current, the duration of the arc(cycles), and the distance
from the arc to the employee
A comparison of these two options

NESC Tables 410-1 & 410-2
 To utilize the tables, you must calculate single phase
to ground fault current and then identify upstream
protective device clearing times.
 Not very accurate for “actual” fault current and
clearing time.

Perform an Arc flash hazard analysis, and
document the incident energy exposure.
 IEEE 1584 (SKM, ETAP, Easypower, Duke Heat Flux,
and others)
 ArcPro Software by Kinectrics
IEEE 1584





Guide for performing Arc Flash Hazard
calculations for incident energy and
determining proper PPE.
Calculations verified over voltage range from
208V to 15kV.
Three-phase arcs in enclosures or open air.
No single phase faults
Shifts from lab tested standard formula to Lee
Method for 25kV faults and above.
 Lee method is based on theoretical behavior of arcs.
 No data indicating Lee Method has been verified for
25kV and above.
ARCPRO



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
Physics based model which calculates the
thermal parameters of electric arcs.
Calculations are very similar to IEEE 1584 for
15kV systems.
Typically utilized for analysis of 25kV systems
and above.
Single-phase arcs in open air only. This is
typically more suited to the majority of
distribution system situations.
Multipliers (adjustment factors) are applied to
incident energy for three phase and faults in a
box (enclosures such as padmounted
transformers.
Arc Flash Analysis Steps
1. Data collection
1. Data Collection
Secure arc flash calculations and upstream
protective device settings from Wholesale
provider
 Bring Electric system maps up to date and
create accurate substation one-lines if not
already available
 Collect substation equipment nameplate
information and protective device settings
 Collect distribution system information to
create typical feeder for overhead and
underground. This includes recloser and fuse
information.

Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose
worst case
2. Determine System operating
modes
 Identify modes of operation:
ie utility
only, extended parallel generation only,
multiple scenarios with generators in
parallel with utility, etc.
 Run the analyses on worst case.
Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose worst case
3. Calculate available fault current throughout system
3. Calculate the available fault
current
 Utilizing data collected in Step 1, create a
system single line and system parameters
in SKM software.
 In SKM, calculate the available fault current
at each bus identified in the system oneline.
 For systems 25kV and above, first calculate
the single phase fault current in SKM,
identify clearing times and then input into
ARCPRO.
Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose worst case
3. Calculate available fault current throughout system
4. Calculate arc flash incident energy levels
4. Calculate incident energy levels
 In SKM, calculate the incident energy
levels at each bus in the system.
 For systems 25kV and above, calculate
the single line to ground incident
energy in ARCPRO, then apply
adjustment factors to convert from
single phase faults to three phase
faults and faults in enclosures (such as
padmounts)
What is Incident Energy?




Unit of measure is cal/cm2 or Joules/cm2
A calorie is the energy required to raise one gram of water one degree
Celsius at one atmosphere.
One cal/cm2 is equivalent to the amount of energy produced by a
cigarette lighter in one second
The onset of second degree burns will occur at 1.2 cal/cm2 per second.
(See chart below)
Incident Energy
(cal/cm2)
1.2
Degree Burn
2nd degree burn to skin
4
Ignite a cotton shirt
8
3rd degree burn to bare skin
Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose worst case
3. Calculate available fault current throughout system
4. Calculate arc flash incident energy levels
5. Calculate arc flash protection boundaries
5. Calculate the Arc Flash Protection
boundaries
 In SKM or ARCPRO, calculate the Arc Flash
Protection boundaries at each bus.
 ARC Flash protection boundaries are an
approach limit measured from exposed live
parts within which an unprotected person
could receive a second degree burn if an
arc flash were to occur.
 Appropriate PPE must be worn inside this
boundary
Arc Flash Protection Boundaries
 Arc
flash hazard and flash protection
boundary varies with:
 Type of equipment and equipment
configuration
 Available short circuit current
 Voltage
 Fault duration – protectice devices upstream
of the arcing fault and their settings.
Approach Boundaries
Note: The flash protection boundary is the distance at which the incident energy
equals 1.2 cal/cm2.
Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose worst case
3. Calculate available fault current throughout system
4. Calculate arc flash incident energy levels
5. Calculate arc flash protection boundaries
6. Determine protective device characteristic and arc
duration
6. Determine protective device
characteristic and arc duration
 Using the SKM software calculate the
clearing times for the available faults.
 Clearing times are determined by the
intersection of the available arcing fault
current and the protective device curve
Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose worst case
3. Calculate available fault current throughout system
4. Calculate arc flash incident energy levels
5. Calculate arc flash protection boundaries
6. Determine protective device characteristic and arc
duration
7. Determine working distances
7. Determine working distances
 IEEE 1584 (SKM) assigns working
distances based on equipment type and
voltage class. (You are permitted to
adjust these distances if within
acceptable range)

ARCPRO calculates incident energy at
various distances. Choose voltage
appropriate distance following footnotes
from NESC table 410-1 and 410-2.
Table 410-2 refers you to or 441-2 for
46kV and above.
Arc Flash Analysis Steps
1. Data collection
2. Determine system operating modes…choose worst case
3. Calculate available fault current throughout system
4. Calculate arc flash incident energy levels
5. Calculate arc flash protection boundaries
6. Determine protective device characteristic and arc
duration
7. Determine working distances
8. Determine required PPE (risk hazard) category
8. Determine required PPE

Using the SKM software calculate the
required PPE category.
Personal Protective Equipment is the
complete clothing system required in order
to prevent an incurable burn during an
arcing fault.
 PPE can include eye protection, ear
protection, face protection, gloves, &
clothing
 Always perform work de-energized if
possible!

Classes of Protective Clothing
Incident
Clothing
Energy
Category
Description
ATPV
(cal/cm2)
0 - 1.2
0
Untreated Cotton
Long Sleeve shirt & Long
pants
n/a
1.2 -4
1
FR shirt and pants
Or FR coverall
Minimum 4
4-8
2
Minimum 8
Cotton Underwear + CL.1
8-25
3
Minimum 25
FR Coveralls + CL.2
25-40
4
Double Layer Switching
Coat + CL.2
ATPV - Arc thermal performance exposure value (cal/cm2)
Minimum 40
Personal Protective Equipment (PPE)
 Category 0
 Long-sleeve shirt and Long pants
○ Made of non-melting/flammable materials
○ Fabric weight at least 4.5 oz/yd2
 Hard Hat
 Safety Glasses
 Leather Gloves
 Leather Work Shoes
PPE
 Category 1 – Minimum Arc Rating of 4
cal/cm2
 FR Shirt and Pants or FR Coverall
 Hard Hat
 Safety Glasses
 Leather Gloves
 Leather Work Shoes
PPE
 Category 2 – Minimum Arc Rating of 8
cal/cm2
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Cotton Underwear plus FR Shirt and FR Pants
Cotton Underwear plus FR Coverall
Hard Hat
Safety Glasses/Goggles
Arc Rated Face Shield or Flash Suit Hood
Hearing Protection
Leather Protectors worn over rubber gloves
Leather Work Shoes
PPE
 Category 3 – Minimum Arc Rating of
25 cal/cm2
 Cotton Underwear plus FR Shirt and FR Pants

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

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plus FR Coverall
Hard Hat with FR Hard Hat Liner
Safety Glasses/Goggles
Flash Suit Hood
Hearing Protection
Leather Protectors worn over rubber gloves
Leather Work Shoes
PPE
 Category 4 – Minimum Arc Rating of 40
cal/cm2
 Cotton Underwear plus FR Shirt and FR Pants plus

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Multilayer Flash Suit
Cotton Underwear plus FR Coverall plus Multilayer Flash
Suit
Hard Hat with FR Hard Hat Liner
Safety Glasses/Goggles
Flash Suit Hood
Hearing Protection
Leather Protectors worn over rubber gloves
Leather Work Shoes
Arc Flash Mitigation

Reduce the Arcing Fault Current
 Current Limiting Protective Devices

Increase the Working Distance
 Operating Devices remotely
○ SCADA
○ Relays and Breaker controls in Equipment
House
 Extension tools

Reduce the Clearing Time
 Lower protective device settings
 Differential relaying
Arc Flash Mitigation
Reduce Clearing Time:

Upstream Circuit Breaker

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


Reduce protective device settings
Enable Instantaneous Trip Function
Disable Reclosing when working on circuit
Utilize “maintenance mode” with alternate Settings if
necessary (digital relays)
Differential relaying
 Removes fault in minimum time (2 or 3 cycles)

Arc Flash relaying
 Compares over current value to light flash
magnitude.
Arc Flash Mitigation

Reduce the Arcing Fault Current
 Current Limiting Protective Devices

Increase the Working Distance
 Operating Devices remotely
○ SCADA
○ Relays and Breaker controls in Equipment House
 Extension tools

Reduce the Clearing Time
 Lower protective device settings
○ Maintenance mode with alternate settings (Digital
relays). Instantaneous covers circuit “backbone”
 Differential relaying

Arc Flash design
Arc Flash Mitigation
Arc Flash Design Strategies:
Relocate Relays & Controls to the
Equipment House
 For new substations perform a preliminary
Arc Flash analysis to aid in design.
 Specify digital relays to provide flexibility
with regards to settings and
communications.
 Specify equipment with an emphasis on
minimizing arc flash exposure.

Arc Flash Mitigation
Safety and Design Considerations:
Arc Flash Boundary
Identified
 Specify Arc Resistant

 MV Switchgear
 LV Switchgear

View Port for Infrared
inspection
Infrared Ports
 Monitoring
without exposure
Arc Flash Mitigation
Safety and Design Considerations:

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Arc Flash Boundary
Identified
Arc Resistant
View Port for Infrared
inspection
Hinged covers vs. bolted
Remote Racking
Mimic Bus (Touch panel)
PPE Storage on site if
necessary
Arc Flash Analysis Example #1

12.47kV system – 12.47kV Circuit Breaker
 Arc Flash Calculation Summary
 Time Current Curve (TCC)

Protected by upstream CO-7 relay
Arc Flash Calculation Summary
12.47kV system
12.47kV Circuit Breaker
12.47kV Circuit Breaker
4640A
Arc Flash Analysis Example #2

12.47kV system – Substation 240V AC
Panel
 Arc Flash Calculation Summary
 Time Current Curve (TCC)

Protected by upstream 3A Fuse
Arc Flash Calculation Summary
12.47kV system
240V AC Panel
240V AC Panel
Arc Flash Analysis Example #3

12.47kV system – 100A Fuse
 Time Current Curve (TCC)
 Arc Flash Calculation Summary

Protected by upstream 3000A breaker
Arc Flash Calculation Summary
12.47kV system
12.47kV 100A FUSE
12.47kV 100A FUSE
Arc Flash Analysis Example #4

100kV system – 100kV Circuit Switcher
 Arc Flash Calculation Summary – NESC 2007
 Arc Flash Calculation Summary – NESC IEEE 1584
 ArcPro Total Heat Flux Calculation
 ArcPro Heat vs. Distance Table

Protected by SEL 587Z Differential Relay
Arc Flash Calculation Summary
100kV system
100kV Circuit Switcher
100kV Circuit Switcher
Apply 3phase adjustment
factor of 2.2 to incident
energy. Total is 1.12
cal/cm@
Arc Flash Calculation Summary
100kV system
100kV Circuit Switcher
100kV Circuit Switcher
Typical Summary of Results
69kv & 100kV equipment can range from Category 0 to
Dangerous
 This is dependent upon working distance and
clearing time
 We recommend all work be performed de-energized
 Most equipment on overhead 15kV and 25kV lines is
Category 1. Category will increase is instantaneous
function is disabled or fault location is past pickup.
 Transformers
 Secondary side below 240V

○ Category 0
 Secondary side of 240V, less than 125 KVA
○ Category 0
 Secondary side of 240V, 125 KVA and above
○ Category 2
Typical Summary of Results
Transformers – Secondary side of large
transformers (208V or 480 V) have potential
for high incident energy levels.
 Typical Hazard Risk Categories:


Transformer Size
PPE Category
Up to 300 KVA
Category 2
500 KVA to 1000 KVA
Category 3
1000kVA to 1500kVA
Category 4
2000kVA and Over
Dangerous
Perform all work on padmounted transformer
secondaries de-energized if possible.
Typical Summary of Results

Inside Substations
 Line side of Feeder Circuit Breakers have
higher incident energy when the only
upstream device is Wholesale provider’s
relay or Fuse.
 It is better to have control over relay settings
 Load side of Feeder Circuit Breakers
○ Category can be any where from 0 up to 3.



FLASH PROTECTION
Flash Protection Boundary
An approach limit measured from exposed live parts within
which an unprotected person could receive a second
degree burn if an arc flash were to occur. Appropriate PPE
must be worn inside this boundary.
Approach Boundaries
Note: The flash protection boundary is the distance at which the incident energy
equals 1.2 cal/cm2.
Example of “WARNING” Label
Example of “DANGER label”
Brady GlobalMark Printer
How does the Arc Flash Analysis
effect your Safety Program?



Electric Utilities should provide proper PPE for
workers based on results of the study.
Work rules should be enacted for common work
tasks.
Provide customers with arc flash information
 Typically do not provide upstream protective device info.


Contractors must wear properly rated PPE for
work being performed.
Mutual aid work must be coordinated very
carefully when working on other electric systems.
Crews should not work on any equipment that
has available incident energy greater than their
PPE.
Future of Arc Flash
Constantly evolving issue.
 NESC 2012 will most likely have many
changes.

 Proposed new Table 410-1 for voltages from
50 – 1000V (AC) that is Task specific.

Arc Flash research and testing on
systems 15kV and higher will continue.
This should provide better data for future
software programs.
QUESTIONS?
THANK YOU FOR
YOUR TIME
Michael C. Dougherty, PE
A.J. Molnar, PE
Southeastern Consulting Engineers, Inc.
Charlotte, NC