Class 4 (4th Engineer) MET 📅 Sep 2022

Exam Question

(a) Name the three main types of a.c. motors and explain the use of which they are put in marine engineering (6)

(b) A four pole motor is fed at 440V and takes a armature of 50A. The resistance of the armature circuit is 0.28Ω. the armature winding is wave connected with 888 conductors and the useful flux per pole is 0.023 wb. Calculate the speed (10)

Reference Answer

### Part (a): Main Types of A.C. Motors and Their Marine Applications
The three main types of A.C. motors used in marine engineering, along with their specific applications, are as follows:
**1. Three-Phase Squirrel Cage Induction Motor**
* **Principle:** This is the most common type of AC motor used on board ships. It operates on the principle of a rotating magnetic field produced by the three-phase stator winding, which induces a current in the rotor's 'squirrel cage' bars. The interaction between the stator's and rotor's magnetic fields produces torque. It is known for its robust, simple construction, low maintenance requirements, and high reliability.

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