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?

23%
-19%
123%
None of these

LohaHridoy

6 views

2025-01-04 04:42

1 Answers

AhmedNazir

Option 1 : 23%

When T remains constant,

s₁V₁ ² = s₂ V₂ ²

so, s₂/s₁=(V₁/V₂)²=(1/0.9)²=1.23

we know that I ₂ ∝ s V

I’₂ / I₂ =(s₂V₂ / s₁V₁) = 1.2 × 0.9 = 1.107

Now, Cu losses are nearly proportional to I₂²

∴ Cu loss in the 2nd case/ Cu loss in the 1st case = (I ′₂)²/(I₂)² = (1.1072)² = 1.23

Reduction of 10% in line voltage causes about 23% increase in Cu losses.

6 views Answered 2022-09-04 04:29

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