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Class 2 (2nd Engineer) MET 📅 Jun 2019

Exam Question

(a) What are the factors which determine the synchronous speed of a motor? (6)

(b) Three conductors fitted side by side in the stator of a salient-pole alternator. Each generates a maximum voltage of 200V (sinusoidal). The angle subtended at the centre of the stator between adjacent conductors is 20 electrical degrees. If the three conductors are connected in series, find:

(i) The r.m.s. value of the effective voltage and

(ii) The 'breadth factor'. Using the theory that is the basis of this problem, give one reason why three-phase current has been introduced (10)

Reference Answer

(a) The synchronous speed of an AC motor is determined by two primary factors:
Supply Frequency (f)
Number of Poles (P)
The relationship between these factors and the synchronous speed (Ns) is given by the formula:

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