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Introduction to Arc FlashGuest Lecturer: Jon Leman, P.E.
University of Idaho: BSEE 2001, MSEE 2010
U.S. Navy – Physics/Electrical Engineering Instructor (4 years)
POWER Engineers, Inc. – Electrical System Studies (10 years)
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Arc Flash - Description
Arc Flash = Short Circuit Through the Air
Temp. can reach 5000° F Hot Gassing
Molten Metal
Severe Pressure Wave
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Arc Flash - Description
Arc Flash = Short Circuit Through the Air
Temp. can reach 5000° F Hot Gassing
Molten Metal
Severe Pressure Wave
Shrapnel
http://www.youtube.com/watch?v=Hp1JdVwbN_U
http://www.youtube.com/watch?v=hA-w0QAaxRU
http://www.youtube.com/watch?v=FDy6fixKVxc&list=UUa8eW
ErXv1OSBLpQemGEkog
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Arc Flash - Description
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Arc Flash - Theory Thermal aspects of arc flash were first described
mathematically by Ralph Lee in a 1982 paper called
“The Other Electrical Hazard: Electric Arc Blast Burns”.His approach made use of the maximum power transferTheorem.
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Arc Flash - Theory Ralph Lee Method (significant limitations)
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Arc Flash – Calculations (Energy) (Power ⋅ Time) (Voltage ⋅ Current ⋅ Time)
Energy on a surface at a distance d from the source is inverselyproportional to the distance squared
Energy (Voltage ⋅ Current ⋅ Time)
Distance2
=>Easily seen in the Lee equations – Not easily seen inIEEE equations.
Incident Energy is reported in Joules per cm2 or Calories per cm2
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Arc Flash - Theory IEEE 1584 Method: Empirical Equations
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Arc Flash – Industry Standards National Electrical Code (NFPA-70, Revised 2014)
OSHA 29 CFR 1910 (Revised in 2014)
IEEE 1584 (Revised in 2002, revision pending)
NFPA 70E (Revised 2015)
Software Most programs use the IEEE 1584 approach Non IEEE 1584 methods:
Duke Heat Flux ArcPro (by Kinectrics)
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Arc Flash - Description PPE = Personal Protective
Equipment
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Arc Flash – Calculations1. Gather System Data
2. Identify Voltages and Equipment Types3. Select Working Distances
4. Relate computer model to physical equipment
5. Determine Modes of Operation (Worst)
6. Determine Bolted Fault Currents
7. Determine Arcing Fault Currents
8. Determine Duration of Arcs
9. Calculate Incident Energies
10. Calculate Flash Protection Boundaries
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Arc Flash – Calculations
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Note: relays are inserted below breaker they
control. This not typical and was done to get
around a software limitation.
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http://www.apt-power.com/wp-content/uploads/Medium-Voltage-Switchgear-Distribution-Switchgear-APT.pdf Used with permission
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Arc Flash – Considerations Always relate electrical models to the actual physical
system.
Pick the right location for worst case analysis
Be aware of available evacuation space or lack thereof
Higher fault currents and longer clearing times compete forworst case arc flash conditions
Be aware of interrupting device ratings. If fault currentsare too high, it may not be safe to assume the device clears
the fault. Poorly maintained equipment can also fail tointerrupt a fault.
Remember that it takes breakers a finite time to clear a
fault (typical 3-5 cycles).
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Arc Flash – Mitigation Arc resistant gear
More PPE Administrative constraints such as prohibiting energized
work or other procedures that eliminate or reduce
exposure.
Faster clearing times
Reduce pickup/time dial (may need to be temporary and include a
lock-out procedure)
Cubicle flash detecting instantaneous element (arc flash/optical relays)
Remote operation
Reduce fault currents (series reactors).
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Questions?
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