Red Seal Electrician Practice
TransformersQuestion 207 of 1506

Why is a motor-generator set a poorer way to change voltage than a transformer?

  1. It cannot raise or lower the voltage of a supply
  2. It gives back more power than it takes from the supply
  3. Combined losses leave it about 90% efficient or less
  4. It can only run on a direct current supply line
Show answer

Correct answer: Combined losses leave it about 90% efficient or less

The losses of the motor and the generator add up, and the moving parts also wear. A transformer has no moving parts and a much higher efficiency.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 10.2: Step-up and Step-down Transformers

Practice transformers

Questions last reviewed: 18 October 2026