Protection Engineering Basics and Schemes Protection Engineering | Page 177

 Under Voltage Relay
5.6.1 over Voltage Relay (59)
Why voltage gets high? Reasons will be
 Loss of load
 Switching surges
 Lightning Strikes
What happened when Voltages get high?
 Equipment damage
Allowable over voltage is less than 110%, but depend on
utility, when these values reaches and relay send trip
signal selected
breakers trips.
Usually we need
to reduce
generation or we
need to add load
lines to tackle this
issue.
Nowadays over
voltage relay
become over
voltage feature of
pg. 177