Red Seal Electrician Practice
TransformersQuestion 1141 of 1506

A transformer was switched off and left with some magnetism in its core. What effect can this have when it is energized again?

  1. The inrush current is always zero after a shutdown.
  2. The inrush current can be even more severe.
  3. The secondary voltage is reversed for the first cycles.
  4. The core losses vanish.
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Correct answer: The inrush current can be even more severe.

Residual flux adds to the new flux and drives the core deeper into saturation.

Source: Lessons in Electric Circuits II: AC (Kuphaldt), 10.8: Practical Considerations - Transformers

Practice transformers

Questions last reviewed: 18 October 2026