Application Of Protection Inhibits; Blocked Overcurrent Protection; Tripping Output For Adjacent Circuit Breakers - Toshiba GRE110 Instruction Manual

CBF TRIP
Binary output circuit
[RESET]
"Ins"
"Dw"
+
"Dl"
"Lat"
Reset button
+
REMOTE RESET
Figure 2.10.2 Tripping Output for Adjacent Circuit Breakers

2.11 Application of Protection Inhibits

All GRE110 protection elements can be blocked by a binary input signal. This feature is useful in
a number of applications.
2.11.1

Blocked Overcurrent Protection

Conventional time-graded definite time overcurrent protection can lead to excessive fault clearance
times being experienced for faults closest to the source. The implementation of a blocked
overcurrent scheme can eliminate the need for grading margins and thereby greatly reduce fault
clearance times. Such schemes are suited to radial feeder circuits, particularly where substations
are close together and pilot cables can be economically run between switchboards.
Figure 2.11.1 shows the operation of the scheme.
Instantaneous phase fault and earth fault pick-up signals OC1 HS, and EF1 HS of OC1 and EF1
elements are allocated to any of the binary output relays and used as a blocking signal. OC2 and
EF2 protections are set with a short delay time. (For pick-up signals, refer to Figure 2.1.5 and
2.1.6.)
For a fault at F as shown, each relay sends the blocking signal to its upstream neighbor. The signal
is input as a binary input signal OC2 BLOCK and EF2 BLOCK at the receiving end, and blocks the
OC2 and EF2 protection. Minimum protection delays of 50ms are recommended for the OC2 and
EF2 protection, to ensure that the blocking signal has time to arrive before protection operation.
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 a failure of the blocked scheme.
&
≥1
&
TBO
0
&
0.00 – 10.00s
&
S
F/F
R
≥1
 51 
≥1
BO#m
t
Tripping output relay
6 F 2 T 0 1 7 2