Protection Engineering Basics and Schemes Protection Engineering | Page 126

But if fault will occur at point P2 (figure 1), the current
lead voltage by 90 degree and angle
is -
90 degree.
T=KVA cos (-90-90) = KVA cos (-180)
This result in maximum negative torque of rotating disc
(Disc rotate in reverse direction), the movement in
reverse direction will be controlled by mechanical stop.
What happened when there is two source?
The relays at B1 and B2 will be simply overcurrent relay, but relays at B12, B21, B23 and B32 should be
directional overcurrent relay. These all relays should be time delayed to avoid over looping.
Time setting:
fault at
P1
P2
Bus 1
Bus 2
Bus 3
Directional OC relay Operate before any other relay in loop
B21 before B23
B23 before B21
B1 and B21
B12 and B32
B3 and B23
Relays in use (Protection Market)
pg. 126