Red Seal Electrician Practice
TransformersQuestion 1088 of 1506

Why do utilities raise the voltage with transformers before sending power over long lines?

  1. The line resistance drops to zero once the voltage is high enough.
  2. The frequency rises with voltage, which makes the line more efficient.
  3. The transformer adds extra power to the line to cover the losses.
  4. The current is lower, so less power is lost in the line resistance.
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Correct answer: The current is lower, so less power is lost in the line resistance.

For the same power, higher voltage means lower current. Lower current gives smaller I-squared-R losses in the conductors.

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

Practice transformers

Questions last reviewed: 18 October 2026