What is the purpose of a tap changer in a distribution transformer?

• A. To regulate voltage by changing turns ratio
• B. To cool the transformer
• C. To increase efficiency at full load
• D. To protect winding from fault

Answer: (A)

A tap changer changes the transformer’s voltage by altering the number of turns on one winding, which changes the turns ratio between the primary and secondary. By selecting different taps, the transformer can produce a secondary voltage that stays within the required limits even as source voltage or load current varies. This voltage regulation is essential in distribution systems to keep customer voltages stable.

It isn’t a cooling device, so it doesn’t cool the transformer. It doesn’t inherently boost efficiency at full load, and it isn’t a protection device for winding faults. Some tap changers can be operated while the system is energized (on-load) and others require the transformer to be de-energized (off-load), but the purpose remains adjusting the voltage by changing the turns ratio.