Overvoltage
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:
Variations in supply voltage outside the normally accepted limits of ± 10% are subdivided according to the length of the variation.
Long duration variations encompass rms deviations at power frequencies for longer than one minute. EN 50160 specifies the steady state voltage tolerances expected on a power system. A voltage variation is considered to be of long duration when the limits are exceeded for more than 3 minutes (the international standards use a period of one minute).
Long duration variations can be:
- sustained interruptions
- undervoltages
- overvoltages.
Overvoltages and undervoltages generally are not the result of system faults, but are caused by load variations on the system and system switching operations. Such variations are typically displayed as plots of rms voltage versus time.
An overvoltage is an increase in the rms ac voltage greater than 110% at the power frequency for a duration longer than 3 minutes.
Overvoltages are usually the result of load switching (e.g. switching off a large load, or energizing a capacitor bank). The overvoltages result because the system is either too weak for the desired voltage regulation or voltage controls are inadequate. Incorrect tap settings on transformers can also result in system overvoltages.
--BSRIA
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