What do tap changers do?

• A. Raise or lower voltage by changing primary winding.
• B. Change the frequency of the output.
• C. Change the load current by adjusting taps.
• D. Change the transformer core material to adjust voltage.

Answer: (B)

Tap changers regulate voltage by changing the number of turns effectively in use on a transformer winding. By selecting different taps, the turns ratio between the primary and secondary is altered, which raises or lowers the output voltage to keep it within desired limits as loading or line conditions change. The frequency, however, is set by the supply and remains essentially unchanged by tapping, since the magnetic core and flux are driven by the same frequency regardless of which tap is selected. The core material or construction isn’t changed by tapping, and while voltage changes can influence current, tap settings don’t directly “set” load current—the load determines that based on the voltage and the connected equipment. So tap changers are all about voltage regulation through different turns, not about changing frequency.