Voltage interruptions

BSRIA Power quality guide (AG 2/2000) was written by C C Pearson and V Uthayanan and published by BSRIA in July 2000. It states:

An interruption occurs when the supply voltage or load current decreases to less than 10% for a period of time not exceeding 3 minutes. Longer periods of such low voltage are referred to as sustained interruptions.

Interruptions can be the result of power system faults, equipment failures, and control malfunctions. The interruptions are measured by their duration, since the voltage magnitude is always less than 10% of nominal. The duration of an interruption due to a fault on the utility system is determined by the operating time of utility protective devices. Instantaneous reclosing generally will limit the interruption caused by a non-permanent fault to less than 30 cycles. Delayed reclosing of the protective device may cause a momentary or temporary interruption. The duration of an interruption due to equipment malfunctions or loose connections can be irregular.

Some interruptions may be preceded by a voltage sag when these interruptions are due to faults on the source system. The voltage sag occurs between the time a fault initiates and the protective device operates.

--BSRIA

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