Sags - Effect on Equipment

Voltage sags result from a changing current interacting with a power system's impedance. Sags may occur at the utility level, from nearby customers, or from the source building feeding another building. But the main causes of voltage sags are the customer's own loads.

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 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.

When voltage sags are a problem, the first step in solving it is to identify what is being disrupted and why. Where is the load causing the changing current? If that load or group of loads can be located, then a solution may be as simple as relocating either the victim or the culprit. The sag no longer affects the same equipment or the same part of the system.

Since sags are closely dependent on the wiring impedance, another possible solution is to increase the wire size in the distribution path for the sensitive load or loads. This decreases the impedance, ultimately reducing the magnitude of the sag.

Should these steps not be possible, then voltage regulation must be introduced to maintain voltage stability and keep data integrity.

Voltage regulators may be stand-alone devices, or used with other technologies such as transformers to add to their capabilities.