Class 4 (4th Engineer) MET 📅 Sep 2025

Exam Question

(a) Describe the basic principles of self-excited generators. (6)

(b) The armature resistance of a 200V-shunt motor is 0.4 Ohms. The no load (this is the term used when the motor is running light, i.e. not loaded) armature current is 2A and when it is taking an armature current of 50A, the motor speed is 1200 rev/min. Find the approximate no load speed. (10)

Reference Answer

### (a) Basic Principles of Self-Excited Generators (6 Marks)
A self-excited DC generator is one in which the field winding is energized by the current produced by the generator itself, rather than from a separate external DC source. The process relies on residual magnetism in the field poles to initiate voltage generation.
#### 1. Fundamental Principle
The operation is based on Faraday's Law of Electromagnetic Induction. When an armature conductor is rotated within a magnetic field, an electromotive force (EMF) is induced in it. For a self-excited generator, the key is how this magnetic field is created and sustained.

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