Class 4 (4th Engineer) MET 📅 May 2024

Exam Question

(a) What are the different types of DC motors? (6)

(b) A 10 H.P. 230 V shunt motor takes an armature current of 6A from 230 V mains at no load runs at 1200 r.p.m. The armature resistance is 0.25Ω. Determine speed and electromagnetic torque when the armature takes 36 amps. with the same flux. (10)

Reference Answer

### (a) Different Types of DC Motors
Direct Current (DC) motors are classified primarily based on the method of connecting their field windings in relation to the armature circuit. This connection dictates the motor's operating characteristics, such as speed-torque relationship, speed regulation, and starting torque, thereby determining their suitability for various marine auxiliary applications. The main types are Shunt, Series, and Compound motors.
#### 1. DC Shunt Motor
* **Construction and Connection**: In a DC shunt motor, the field winding (shunt field) is connected in parallel (shunt) with the armature winding. The shunt field winding consists of a large number of turns of fine wire and has high resistance. It is directly connected across the supply voltage, meaning the field current remains relatively constant and largely independent of the armature current.

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