Class 4 (4th Engineer) MET 📅 Apr 2025

Exam Question

(a) Describe the effect of running an induction motor on reduced voltage. (6)

(b) A 90V d.c. generator is used to charge a battery of 40 cells in series, each cell having an average e.m.f. of 1.9 V and an internal resistance of 0.0025 Ω. If the total resistance of the connecting cells is 1Ω, calculate the value of the charging current. (10)

Reference Answer

### Part (a): Effect of Running an Induction Motor on Reduced Voltage (6 Marks)
Running a three-phase induction motor on a voltage lower than its rated nameplate value has several detrimental effects on its performance and longevity. The fundamental principle is that the torque produced by an induction motor is directly proportional to the square of the applied voltage ($$T \propto V^2$$). Any reduction in voltage will have a significant impact.
Key effects are as follows:
1. **Reduced Torque:**

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