The voltage change rate of a voltage regulator is one of the main performance indicators of a transformer. When a transformer supplies power to a load, the voltage at the load end of the transformer will inevitably decrease. Comparing the decreased voltage value with the rated voltage value, the percentage is taken as the voltage change rate, which can be expressed using a formula; Voltage change rate=[(secondary rated voltage - load terminal voltage)/secondary rated voltage] × 100%. A typical power transformer has a voltage change rate of 4-6% when connected to a rated load.