Generator Overvoltage Relay (59 G)

Overvoltage shouldn’t occur on a generator fitted with an automatic voltage regulator. Overvoltage may be caused by defective operation of the voltage regulator under isolated operation of the generator. The relay detects the over excitation of generators and transformers by measuring the over voltage.


Data for setting calculation

Generator Voltage------------------------------------19000 V
VT turns ratio ----------------------------------------19000 / 100 V = 190
The max. permissible voltage for continuous load operation — 105 %
The max. permissible voltage for no-load operation -------------- 110 %
The max. permissible transient overvoltage ------------------------ 120 %

Relay Setting

Setting Conditions
The trip pickup is intended for moderate overvoltage of long duration.
Pickup < The max. Permissible transient overvoltage .
= 19000 / 190 * 1.20
= 120 V