Red Seal Electrician Practice
TransformersQuestion 1137 of 1506

DC current flows in a transformer primary winding. What is the effect on the core?

  1. It cools the core and so lowers the core losses.
  2. It cancels the eddy currents in the laminations.
  3. It pushes the flux toward saturation on one half-cycle.
  4. It lowers the resistance of the primary winding.
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Correct answer: It pushes the flux toward saturation on one half-cycle.

The DC adds an offset to the alternating flux, so one half of the cycle gets closer to saturation.

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

Practice transformers

Questions last reviewed: 18 October 2026