GATE EE 2018 Set 1 — Question 31
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Power Systems → Fault Analysis → Unsymmetrical Faults (LG, LL, LLG)
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Question
The positive, negative and zero sequence impedances of a 125 MVA, three-phase, 15.5 kV, star-grounded, 50 Hz generator are pu, pu and pu respectively on the machine rating base. The machine is unloaded and working at the rated terminal voltage. If the grounding impedance of the generator is pu, then the magnitude of fault current for a b-phase to ground fault (in kA) is __________ (up to 2 decimal places).
Correct answer
73 to 74
Solution
1.Calculate Base Current ():
2.Fault Current in per-unit ():
For a single line-to-ground fault (whether a, b, or c phase), the magnitude of the fault current is given by:Given:
- pu (rated terminal voltage)
- pu
- pu
- pu
- pu (grounding impedance)
3.Convert to kA:
The magnitude of the fault current is approximately 73.53 kA, which falls within the range [73.0, 74.0].Continue learning with Success Tracker
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