Exam Question
Q2
Sketch and describe the method of speed control of synchronous motors by variable frequency. State the advantages of this method over the other methods of speed control.
(16)
ETO
ETO Exam papers
📅 Jan 2026
Reference Answer
### **Part 1: Principle of Synchronous Motor Speed Control**
The speed of a synchronous motor is determined by the frequency of the AC supply and the number of poles in the motor's construction. This relationship is fixed and is known as the synchronous speed ($$N_s$$).
#### **Fundamental Formula**
The synchronous speed is given by the formula:
The speed of a synchronous motor is determined by the frequency of the AC supply and the number of poles in the motor's construction. This relationship is fixed and is known as the synchronous speed ($$N_s$$).
#### **Fundamental Formula**
The synchronous speed is given by the formula:
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