Voltage Sags - Utility

Like all sags, utility-based sags are the result of load changes and system impedance. In this case, however, the customer has no control over the load changes. As far as the customer is concerned, the source voltage at the service entrance dipped.

When a sag occurs, the electronic device's power supply uses some of its stored energy to compensate for the loss of input voltage. If enough energy is lost due to the sag, then the power supply can no longer keep the system operating, and it shuts down. Since the switch is still on, as soon as the sag is over and the voltage has returned to nominal, the system turns back on, or restarts.

The lost energy from the sag may not be enough to shut down the device, but only enough to confuse the digital components. If this happens, then a lock-up may result.

Some form of voltage regulator or energy storage device is needed to remedy these types of disturbances. Products that provide longer ride-through such as enhanced power supplies, that regulate the voltage such as tap-switching conditioners, or that switch to temporary back-up power like an SPS will all suffice.