Class 4 (4th Engineer) MET 📅 Apr 2024

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. When loaded and 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 that uses its own output voltage to energize its field windings, thus producing the magnetic flux required for operation. The process relies on a phenomenon known as residual magnetism.
**1. Core Principle: Residual Magnetism**
- The iron cores of the field poles retain a small amount of magnetism even when the generator is stopped. This weak magnetic field is called residual magnetism and is the starting point for voltage generation.

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