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.