Question

Which of the following motors is expected to have maximum full-load efficiency?

• A. \( 1 \, \text{kW} \)
• B. \( 5 \, \text{kW} \)
• C. \( 30 \, \text{kW} \)
• D. \( 100 \, \text{kW} \)

Hint:

Larger motors tend to have higher full-load efficiency because losses form a smaller fraction of the total power output.

Answer 1

The Correct Option is D

Step 1: The efficiency (\( \eta \)) of an electric motor is given by: \[ \eta = \frac{\text{Output Power}}{\text{Input Power}} \times 100% \] 
Step 2: Larger motors generally have higher full-load efficiency because: - Larger motors operate with lower relative losses. - Copper and iron losses are better managed. - Stray losses become negligible compared to output power. 
Step 3: The efficiency of small motors (e.g., 1 kW or 5 kW) is lower due to: - Higher friction and windage losses. - Larger percentage of stray losses. 
Step 4: Among the given options, the 100 kW motor has the highest expected full-load efficiency due to better energy conversion and reduced relative losses.