Protection Engineering Basics and Schemes Protection Engineering | Page 180

5.6.2 under Voltage Relay (27):
Why systems have over voltage? Because of load loss
mainly, now vice versa applicable here, when load
increase then voltage decreases
Main Reasons of overloading are
 Tripping of transmission lines
 Loss of Generation
Usually 90 to 95% under voltage values are set for under
voltage relay pick up , but again it depend on the utility
power supplier, up to which level their system sustain
under voltage.
pg. 180