Class 4 (4th Engineer) MET 📅 Jul 2024

Exam Question

(a) With reference to single phasing applied to a.c. motors: (8)

(i) Explain the meaning of single phasing;

(ii) Describe its effect;

(iii) State the most common cause of single phasing.

(b) Sketch a simple diagram of a direct on line starter, showing in detail the overload and single phase protection trip. (8)

Reference Answer

### (a) Single Phasing in A.C. Motors
**(i) Meaning of Single Phasing**
Single phasing is a fault condition occurring in a three-phase electrical system where one of the three phases is lost or disconnected from a running or stationary three-phase AC motor. The motor, designed to operate on a balanced three-phase supply, is consequently forced to operate on a single-phase supply. This can result from an open circuit in one of the supply lines, a blown fuse in one phase, or a faulty contactor pole.
**(ii) Effect of Single Phasing**

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