Voltage sag and interruption are commonly related to power quality problems. Voltage sag refers to voltage dips typically for 0.5 to 30 cycles.
During sag, RMS voltage dips with 10% to 90% (Fig. 1). They usually occur due to switching faults on heavy loads. A transitory interruption lasts from 2 seconds to 5 seconds. This sag affects power electronic loads and computer system adjustable speed drives.
Fig. 1: Waveform explaining voltage sag.