Q9. With reference to reverse power protection for A.C. generators operating in parallel:
(a) explain why traditional reverse power relays, operating on mechanical principles, have been replaced by electronic digital microprocessor types; (2)
(b) describe, with the aid of a sketch, a generator reverse power protection circuit that uses an electronic phase sensitive detector. (8)
Q10. With reference to a.c switchboards:
(a) State with reasons, the protective devices that are fitted; (5)
(b) state why a breaker may fail to open under prolonged low voltage conditions. (2)
(c) explain the actions to be taken should a main generator circuit breaker stay connected despite repeated efforts to trip it off the board. (3)
Q9. (a) Describe, with the aid of a sketch, the constructional details of a squirrel cage rotor as fitted in an induction motor (7)
(b) Explain why some rotors have a double cage. (3)
Q11.With reference to insulation testing of electrical equipment:
(a) With reference to insulation testing and why it is carried out on a regular basis; (2)
(b) Describe the procedure for taking a set of insulation readings on an electric motor insitu, stating the minimum acceptable readings; (6)
(c) Explain the term polarisation Index (2)
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