Voltage swell
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:
A swell is defined as an increase to between 110% and 180% of nominal rms voltage or current at the fundamental frequency for durations from 0.5 cycle to one minute.
As with sags, swells are usually associated with system fault conditions, but they are not as common as voltage sags. One way that a swell can occur is from the temporary voltage rise on the unfaulted phases during a single line-to-earth fault.
Swells are characterised by their magnitude (rms value) and duration. The severity of a voltage swell during a fault condition is a function of the fault location, system impedance, and earthing. The term momentary overvoltage is used by many writers as a synonym for the term swell.
--BSRIA
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