DOC. MIE91093 Rev. 1.34
Page 32 of 145
1.4
R
EVERSE POWER RELAY TESTING
1.4.1. Introduction
Reverse power relays can be either wattmetric or varmetric.
The following note applies to both of them; the only difference
is the phase angle between current and voltage.
Reverse power relays normally protect generators against
reverse power. In fact, when the active power flows from the
network to the generator, it means that the generator works
as a motor (that’s the reason why, sometimes, these
protective relays are called
anti-motoring relays
). This may
cause serious problems because the generator receive power
from either turbine and network.
Therefore this power will be transformed in:
Kinetic energy: the generator accelerates;
Thermal energy: the temperature increases.
GENERATOR
MOTOR
Z
S
V
I
E
0
Forbidden
zone
I
jX
s
I
R
s
I
Eo
V
P
Q
Q
P
In other words, if the flux of power is not promptly
interrupted, the life of the generator is seriously in danger.
