Zero-Phase Current Differential Protection - Toshiba GRL100-701B Instruction Manual

Tripping output signals can be blocked by the PLC command DIF_BLOCK and CRT_BLOCK.
The output signals of DIF-A, DIF-B and DIF-C are also blocked when a communication circuit
failure is detected by the data error check, sampling synchronism check or interruption of the
receive signals. For DIF-A_FS, DIF-B_FS and DIF-C_FS signals, see Section 2.2.4.
The differential elements DIF have a percentage restraining characteristic with weak restraint in
the small current region and strong restraint in the large current region, to cope with CT
saturation. (For details of the characteristic, see Section 2.16.)
Erroneous current data may be transmitted from the remote terminal when the remote relay is
out-of-service for testing or other purposes. To prevent false operation in this case, the relay sets
the receiving current data to zero in the differential current calculation upon detecting that the
remote terminal is out-of-service.
If the relay is applied to a three-terminal line, the zero setting is performed only for the current
data received from an out-of-service terminal.
Figure 2.2.2.2 shows the remote terminal out-of-service detection logic. The local terminal
detects that the remote terminal is out-of-service by receiving a signal LOCAL TEST which is
transmitted when the scheme switch [L. TEST] is set to "ON" at the terminal under test. As an
alternative means, the local terminal can detect it by using the circuit breaker and disconnector
status signal CBDS-A, B and C transmitted from the remote out-of-service terminal. The signal
CBDS-A is "1" when both the circuit breaker and disconnector are closed. Thus, out-of-service
is detected when either the circuit breaker or disconnector is open in all three phases.
Zero setting of the receive current data is also performed at the terminal under test. If the scheme
switch [L. TEST] is set to "ON" or the signal R.DATA_ZERO is input by PLC, all the receive
current data transmitted from the in-service terminal is set to zero and this facilitates the local
testing. The zero setting of the receive current data is not performed by the alternative way as
mentioned above.
The out-of-service detection logic can be blocked by the scheme switch [OTD].
LOCAL_TEST1
R.DATD_ZERO
1623
CBDS-A
CBDS-B
CBDS-C
[OTD]
(+)
" "
ON
(∗) Out-of-service detection logic for the remote 2 is same as above.
Note: When a communication circuit is disconnected or communication circuit failure occurs, do
not close the circuit breaker. When closing it, make sure that the DIF element is blocked.
(Otherwise, it may cause malfunction.)
2.2.3

Zero-phase Current Differential Protection

The GRL100 provides sensitive protection for high-impedance earth faults by employing
zero-phase current differential protection. For more sensitive protection, residual current is
introduced through an auxiliary CT in the residual circuit instead of deriving the zero-phase
current from the three phase currents.
The zero-phase current differential element has a percentage restraining characteristic with weak
≥1
≥1
1
&
[Open1]
(+)
" "
ON
Figure 2.2.2.2 Out-of-Service Detection Logic
 13 
1
≥1
1
≥1
REM1_IN_SRV: Remote 1 in-service
REM1_OFF_SRV: Remote 1 out-of-service
REM1_NON_USE: Remote 1 not used
6 F 2 S 0 8 5 0
207
REM1_IN_SRV
208
REM1_OFF_SRV
209
REM1_NON_USE