What is transformer voltage regulation and what factors affect it?

Voltage regulation is the percentage change in secondary voltage from no-load to full-load: VR = (Vno-load - Vfull-load)/Vfull-load x 100%. Factors affecting regulation include: winding resistance (causes IR drop), leakage reactance (causes IX drop), load power factor (lagging PF worsens regulation, leading may improve it), and tap position. Good transformers have regulation below 5%. Voltage regulation is calculated from equivalent circuit parameters or measured by open-circuit and short-circuit tests.