Voltage regulators are adjustable step-up or step-down transformers that help maintain adequate voltage on long distribution lines. For customers located a long distance from a substation, low voltage can be a problem, especially when system load is high. To correct this, voltage regulators can be installed at various points along a distribution line. These devices can raise voltage several percentage points, creating acceptable voltage for those customers located further down the distribution line. They can also lower voltages in situations where a lower than anticipated load results in higher than desired voltage.
The amount of voltage change is adjusted through use of a device called a tap changer, which has multiple settings allowing it to connect into different points on the load side transformer coil. The connection point determines the amount of voltage change. Some voltage regulators adjust voltage automatically while others, typically the older ones, require a crew to adjust them manually. Voltage regulators typically allow voltage to be changed from +10 to -10 percent, however there are some that allow a slightly wider range.