EE1PEEE Refresher Class

Power Part 6

notes by T. Ernst

EE1 – Power Part 6 Notes Fall 2011, Page 1

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EE1 – Power Part 6 Notes

• Sequence Impedances• T-Lines• Rotating Machines• Transformers

• Short Circuit Calculations• 3-phase faults• Phase-phase faults• Phase-ground faults• Phase-phase-ground faults

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EE1 – Power Part 6 Notes

Symmetrical components

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EE1 – Power Part 6 Notes

Sequence impedances

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EE1 – Power Part 6 Notes

T-line sequence impedances

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EE1 – Power Part 6 Notes

Rotating machine sequence impedances

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EE1 – Power Part 6 Notes

Transformer sequence impedances

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EE1 – Power Part 6 Notes

Transformer zero sequence impedance: Connection dependent

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

Neutral impedances

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EE1 – Power Part 6 Notes

Delta – GrdY Transformers

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EE1 – Power Part 6 Notes

Three winding transformers

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

Fault Calculations and Superposition Theory

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EE1 – Power Part 6 Notes

Load current versus fault current

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EE1 – Power Part 6 Notes

3-Phase Faults

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EE1 – Power Part 6 Notes

3-Phase Faults

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EE1 – Power Part 6 Notes

Phase-phase faults

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EE1 – Power Part 6 Notes

Phase-phase Faults

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EE1 – Power Part 6 Notes

Phase-ground Faults

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EE1 – Power Part 6 Notes

Phase-ground Faults

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EE1 – Power Part 6 Notes

Phase-ground Faults

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EE1 – Power Part 6 Notes

Phase-phase-ground Faults

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EE1 – Power Part 6 Notes

Phase-phase-ground Faults

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EE1 – Power Part 6 Notes

Example ProblemFeeder from Large Utility System

480V Main Bus

23,000 – 480 GY Volt

5700/6000/6500 KVA

Z = j8.7%

GENHydro Generator

1000 KVA, 460V

Impedance data (see next page)

Remote 480V Bus

Calculate all types of faults here

0.1 Miles

500 KCMil Aluminum

PVC Conduit

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EE1 – Power Part 6 Notes

XD = synchronous impedance = j1.25 pu

XD’ = transient impedance = j0.30 pu

XD’’ = sub-transient impedance = j0.30 pu

X2 = negative sequence impedance = j0.48 pu

X0 = zero sequence impedance = j0.19 pu

all at generator base of: 1000 KVA, 460 V

Generator Z

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EE1 – Power Part 6 Notes

Solution approach:1. Define system pu bases2. Calculate all component impedances on system

base3. Draw positive, negative and zero sequence

networks4. Reduce sequence networks to equivalent sequence

impedances5. Calculate each type of fault

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes

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EE1 – Power Part 6 Notes