A three phase induction motor is driving full-load torque which is independent of speed. If the line voltage drops to 90% of the rated value, % increase in motor copper losses
- A. 23%
- B. –18%
- C. 123%
- D. None of these
Answer: A. 23%
Explanation: Torque T ∝ sV² is constant, so s ∝ 1/V². Motor current I ≈ sV/R2 ∝ 1/V. When voltage drops to 0.9 V, current rises to I/0.9 = 1.111 I, and copper losses (I²R) increase to (1/0.9)² = 1/0.81 = 1.2346 (+23.5% ≈ 23%).