How does a tap changer affect transformer voltage regulation under varying load?

• A. It adjusts the turns ratio to maintain the desired output voltage as load changes.
• B. It changes the transformer capacity rating.
• C. It changes the cooling method.
• D. It alters the frequency.

Answer: (A)

Managing voltage under varying load relies on adjusting the transformer’s turns ratio. A tap changer lets the transformer add or remove turns on its winding, which directly changes the voltage transformation ratio. When load increases and the voltage at the secondary would otherwise drop, shifting to taps with more turns raises the secondary voltage back toward the desired setpoint. When load falls, taps with fewer turns can lower the secondary voltage to avoid overvoltage. This is the mechanism that keeps output voltage stable as demand changes.

The other ideas don’t regulate voltage in this way. Changing the transformer’s capacity rating isn’t what a tap changer does, since capacity is a fixed design parameter. Altering the cooling method affects heat management, not the voltage level. Changing frequency isn’t controlled by the transformer tap; system frequency is determined by the grid and generation, not by tap adjustments.