Tap changers on distribution transformers are designed to be operated while the transformer is energized and under full load.

• A. False
• B. True
• C. Sometimes
• D. Never

Answer: (A)

Tap changers adjust the voltage by changing which winding taps are connected, and doing that while current is flowing can cause arcing, excessive wear on contacts, and insulation stress. For most distribution transformers, taps are changed only when the transformer is de-energized (off-load) to avoid interrupting service and to protect the switching equipment. There are on-load tap changers that can operate under load, but these are specialized, more complex devices used in specific designs, not universal for all distribution transformers. Because the statement implies every tap changer is designed to be operated while energized and under full load, it isn’t generally true; the common, safe practice is to change taps off-load.