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

• A. It maintains voltage by adjusting cooling.
• B. It changes the insulation type.
• C. It modifies transformer turns ratio during maintenance only.
• D. It automatically adjusts the turns ratio to maintain the desired output voltage as load changes.

Answer: (D)

Voltage regulation under varying load is achieved by a tap changer that automatically adjusts the transformer turns ratio to keep the output voltage steady as loading changes. When the load increases and voltage tends to sag, the tap changer shifts to a higher-turns tap to raise the secondary voltage back toward the desired level; when load decreases and voltage risk overshoots, it can move to a lower-turns tap to lower the voltage. An automatic on-load tap changer continuously senses the output voltage and makes small, real-time adjustments to stay within the target band. Other options don’t influence the voltage seen by customers—cooling changes affect thermal performance, insulation type has no role in voltage, and changing turns ratio only during maintenance wouldn’t respond to actual load changes.