When performing a voltage regulator check on a transformer, which readings are most important?

• A. Primary and secondary voltages under load; regulation percentage
• B. Ambient temperature and humidity
• C. Leaf spring tension and mechanical play
• D. Wire resistance and insulation temperature

Answer: (A)

Voltage regulation performance on a transformer is determined by how the output voltage holds up under load. The most important readings are the voltages on the primary and the secondary while the transformer is delivering rated current, i.e., under load, and the percentage regulation. Checking the primary and secondary voltages under load verifies that the regulator is adjusting taps or impedance so the secondary voltage stays within spec as current changes. The regulation percentage then tells you how much the voltage will shift from no-load to full-load, expressed as a percentage of the full-load voltage. A small, acceptable regulation means the regulator is doing its job well; a large regulation indicates the voltage drifts too much with load. Ambient conditions or mechanical components and general insulation or resistance measurements are relevant for broader equipment health but do not directly assess how well the voltage regulator maintains voltage under changing load.