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Q7) With reference to shipboard electrical distribution systems:

(a) describe the meaning of the term earth fault; (2)

(b) explain why insulated neutral is preferred for low voltage systems; (3)

(c) sketch a circuit diagram of one arrangement for detecting phase to earth faults in   a three-phase system supplied by a star connected generator with earthed neutral resistor (NER); (6)

(d) calculate the ohmic value of an NER to limit the earth fault current to the full load rating of a 2MW, 0.8 p.f., 3.3 kV, three-phase neutral earthed a.c generator. (5)