Class 4 (4th Engineer) MET 📅 Jul 2025

Exam Question

(a) Explain how excitation of the rotor is produced and supplied. (6)

(b) A 25 kVA, single phase transformer has 250 turns on the primary and 40 turns on the secondary winding. The primary is connected to 1500 V, 50 Hz mains calculate (10)

(i) secondary emf

(ii) primary and secondary current on full load

(iii) maximum flux in the core.

Reference Answer

### Part (a): Rotor Excitation Production and Supply
Excitation is the process of generating a magnetic field in the rotor of a synchronous generator (alternator). This magnetic field is essential for inducing an electromotive force (EMF) in the stator windings as the rotor turns. The supply of excitation is achieved through a controlled Direct Current (DC) applied to the rotor field windings. The most common method on modern vessels is the Brushless Excitation System.
**1. Principle of Operation:**
According to Faraday's Law of Electromagnetic Induction, an EMF is induced in a conductor when it cuts through magnetic flux lines. In an alternator:

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