Mains Electricity - Voltage Regulation

Voltage Regulation

To maintain the voltage at the customer's service within the acceptable range, electrical distribution utilities use regulating equipment at electrical substations or along the distribution line. At a substation, the step-down transformer will have an automatic on-load tap changer, allowing the ratio between transmission voltage and distribution voltage to be adjusted in steps. For long (several kilometers) rural distribution circuits, automatic voltage regulators may be mounted on poles of the distribution line. These are autotransformers again with on-load tapchangers to adjust the ratio depending on the observed voltage changes.

At each customer's service, the step-down transformer has up to five taps to allow some range of adjustment, usually ±5% of the nominal voltage. Since these taps are not automatically controlled, they are used only to adjust the long-term average voltage at the service and not to regulate the voltage seen by the utility customer.