arc flash analysis and protection [t. short, 4/12/2013]
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Arc Flash Analysis and Protection
Tom Short, tshort@epri.com
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Larger Panel Test Results
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Larger Panel Test Results
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Padmounted Transformers
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PG&E Padmounted Transformer Tests
2.2 cycles
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Arc Energy Increases in Proportion to:
•Fault current
•Duration •Arc length
P = I × V Voltage per unit length stays about the same.
~ 35 V/inch or 420 V/ft
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Filtered View
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Filtered View
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Arc Elongation
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Quiz time:
If the available fault current is twice as high, what happens to incident energy? Assume a 0.2-sec clearing time.
1)Stays the same
2)About doubles
3)Almost quadruples (I2t)
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Quiz time:
Comparing a 25-kV system to a 12.5-kV system. Which is true (assuming the same fault current).
1)25-kV energy is about 2 times the 12.5-kV energy
2)25-kV energy is about equal to the 12.5-kV energy
3)None of the above
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Protection Options
• Better flame-retardant clothing – Shirts, pants – Face protection – Flash suits
• Better work practices
• Faster relaying
• Lower fault currents
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Analysis Approaches
• NESC tables
• NFPA tables
• Study
– IEEE 1584 – ARCPRO
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2007 NESC
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2012 NESC
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Quiz time:
Which scenario has the worst arc flash hazard?
1)480-V transformer secondary compartment 20 kA available fault current
2)480-V self-contained meter 10 kA available fault current
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PMH Switch Testing at PG&E
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Fault Initiation
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Test Results
Heat rate = 19.5 cal/cm2/sec working distance = 48” Iarc = 6.0 kA V = 21 kV
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Comparisons of Tests and Predictions
Test: 48” working distance 20 cycles duration 6.3 kA Results: 6 cal/cm2
ARCPRO 4” arc Results: 0.38 cal/cm2
IEEE 1584 Grounded; switchgear Results: 0.7 cal/cm2
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More information
• Video summary of EPRI research
– http://youtu.be/fZP47mlELSc
• Papers – Short, T.A.; Eblen, M.L., "Medium-Voltage Arc Flash in Open Air
and Padmounted Equipment," Industry Applications, IEEE Transactions on , vol.48, no.1, pp.245,253, Jan.-Feb. 2012.
– Eblen, M.L.; Short, T.A., "Arc-Flash Testing of Typical 480-V Utility Equipment," Industry Applications, IEEE Transactions on , vol.48, no.2, pp.581,592, March-April 2012.
– Reports on www.epri.com
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