A Transformer will generally provide a higher output voltage when no load is attached to it than when the transformer is fully loaded at nameplate capacity. Stated differently, under load, a transformer’s output voltage drops slightly.
Transformer’s Regulation is the ratio of the difference between transformer’s No Load Output Voltage to its Full Load Output Voltage expressed as a Percentage (%).
For example, suppose a transformer has a No Load Voltage of 240 volts and a Full Load Voltage of 230 Volts. The transformer’s Regulation is calculated as follows.