Blocked Busbar Protection - Toshiba GRE110 Instruction Manual

2.11.2

Blocked Busbar Protection

GRE110 can be applied to provide a busbar zone scheme for a simple radial system where a
substation has only one source, as illustrated in Figure 2.11.2.
For a fault on an outgoing feeder F1, the feeder protection sends a hardwired blocking signal to
inhibit operation of the incomer, the signal OC1 HS and EF1 HS being generated by the
instantaneous phase fault, and earth fault pick-up outputs of OC1 and EF1 allocated to any of the
binary output relays. Meanwhile, the feeder is tripped by the OC1 and EF1 elements, programmed
with inverse time or definite time delays and set to grade with downstream protections.
The incomer protection is programmed to trip via its instantaneous elements OC2 and EF2 set with
short definite time delay settings (minimum 50ms), thus providing rapid isolation for faults in the
busbar zone F2.
At the incomer, inverse time graded operation with elements OC1 and EF1 are available with the
scheme switch [MOC1] setting, thus providing back-up protection in the event of failure of the
blocked scheme.
GRE110 integrated circuit breaker failure protection can be used to provide additional back-trips
from the feeder protection to the incomer, and from the incomer to the HV side of the power
transformer, in the event of the first trip failing to clear the earth fault.
In the case of more complex systems where the substation has two incomers, or where power can
flow into the substation from the feeders, then directional protection must be applied (refer to
GRE140 directional overcurrent protection).
GRE110
OC2 / EF2
High
Speed
Block
Figure 2.11.1 Blocked Overcurrent Protection
 52 
GRE110
OC2 / EF2
OC1HS /
EF1HS High
Speed
Block
6 F 2 T 0 1 7 2
F
Trip
GRE110
OC2 / EF2
OC1HS /
EF1HS