resistance of 8 Ohms is used to ground a 30-MVA, 11 kV alternator. Its relay is set to operate when a 2.2 A out of balance current occurs. The CTs have a ratio of 1000/6. If we consider the reactance of the alternator to be negligible, how much percentage of the stator winding is protected against earth faults? To make this 95%, what is the minimum value of earthing resistance to be used?

resistance of 8 Ohms is used to ground a 30-MVA, 11 kV alternator. Its relay is set to operate when a 2.2 A out of balance current occurs. The CTs have a ratio of 1000/6. If we consider the reactance of the alternator to be negligible, how much percentage of the stator winding is protected against earth faults? To make this 95%, what is the minimum value of earthing resistance to be used?

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.56P: Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit...

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