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Q8. (a) Sketch a labelled circuit diagram for a 440V, step-down, star connected, three-phase autotransformer with 50%, 65% and 80% tappings. Indicate primary and secondary phase turns, voltages and currents. (5)

(b) State TWO advantages and the main disadvantage of an autotransformer compared to a double wound transformer. (3)

(c) A three-phase, 440 V induction motor having a full-load current of 75 A is connected to the 65% tappings of the autotransformer in Q6(a). The motor starting current is 6 x full-load when started D.O.L.

Calculate EACH of the following at start:

(i) the current in each section of the transformer phases. (4)

(ii) the voltage across each section of the transformer phases. (3)

(iii) the motor line voltage. (1)