Correct option is D
Voltage regulation of a transformer is a measure of the change in secondary voltage from no-load to full-load conditions and is expressed as a percentage of the no-load voltage. It can be positive or negative depending on the power factor of the load.
Lagging Power Factor: When the load power factor is lagging, the voltage regulation is typically positive. This is because the inductive nature of the load causes the secondary voltage to drop more under load conditions due to the increased voltage drop across the winding impedance.
Unity Power Factor: When the load power factor is unity, the voltage regulation is generally small but still positive. There is no reactive component to cause additional voltage drop, but the resistive component of the impedance still results in a slight voltage drop.
Leading Power Factor: When the load power factor is leading, the voltage regulation can become negative. This is due to the capacitive nature of the load, which can cause a rise in voltage under load conditions due to the leading reactive current causing a voltage rise in the transformer.
Therefore, both unity and lagging power factors result in positive voltage regulation, while a leading power factor can result in negative voltage regulation. Hence, the correct answer is Unity and lagging.
