TransformerVoltage regulation and efficiency

Voltage Regulation

Since at no-load, Vs = Vp/a

If the transformer equivalent circuitIs in the per-unit system.

Usually it is a good practice to have as small a voltage regulation as possible. For an ideal transformer, VR = 0 percent. It is not always a good idea to have a low-voltage regulation, though sometimes high-impedance and high-voltage regulation transformers are deliberately used to reduce the fault currents in a circuit.

Transformer Phasor Diagram

Phasor diagram of a transformer operating at lagging power factor, voltage regulation of a transformer with lagging loads must be greater than zero.

Transformer Phasor DiagramAt unity power factor, Voltage regulation is greater than 0 but smaller compared to lagging current.

At leading power factor, Voltage regulation is negative

Transformer EfficiencyTransformer’s efficiency equations

Transformer’s losses1. Copper losses (these losses are accounted for by the

series resistance in the equivalent circuit)2. Hysteresis losses (losses include in resistor Rc)3. Eddy-current losses (also included losses in resistor Rc)

Example 1A 15-kVA, 2300/230-V transformer is to be tested to determine it’s excitation branch components, it’s series impedances, and it’s voltage regulation. The following test data have been taken from the transformer.