Toshiba GR200 Series Instruction Manual page 107

DIFL applied to protect the blind zone
A blind zone can be protected at which the DIFL function operates together with open-
terminal-detection function† that can detect the line being taken out of service using the signal
of a breaker(CB) or a disconnector(DS) opened remotely. Consequently, when the line is taken
out of service, the DIFL function turns current data received from the remote-terminal to zero;
then the DIFL function starts to operate with the absence of remote current data. That is, the
DIFL function begins to operate like a simple over current relay.
†Note: The open-terminal-detection function opiates when the user set On for the scheme
switch [OTD]. For more information, see the chapter
Transmission control function
Figure 2.8-1 illustrates the blind zone, which lies between DS H and CB H . If a fault occurs
within the bind zone, a busbar protection at the busbar-H may issue a trip signal for the CB H
at first. However, if the fault remains after the issue‡, the fault current (I F ) enters from the
busbar-G. This phenomenon is an external fault in the DIFL function; we know that the DIFL
function cannot issue a trip signal for the occurrence of the fault. The open-terminal-detection
function is effective for the fault where a blind zone.
‡Note: The fault may be cleared by remote backup protection following a time delay, but
there is a danger of damage being caused to power system plant. The removal of
kinds of this fault is desirable quickly.
The Figure 2.8-1 also illustrates that the CB H and DS H conditions are obtained remotely;
hence, the DIFL function at the terminal-G can operate with only local current data (I G ).
Consequently, the fault can be cleared by issuing the trip signal at the terminal-G. This is
because the remote current data (I H ) turns to zero as explained above.
The user should note that a CB closing command should be injected to the function of
communication application (COMM_APPL‡) at the remote terminal. This is because that the
DIFL function should be secured from an unwanted operation that can be brought by the CB
closing of manual operation and/or autoreclosing operation. The unwanted operation may be
caused due to that the close timing of the CB auxiliary contact (52a) is delayed relative to the
CB main contact. Therefore, the CB closing command should be injected to the open-terminal-
detection function prior to the CB main contact being closed; the injection points are provided
at PLC connection points "CB1 CLOSE COMMAND" and "CB2 CLOSE COMMAND" in the
COMM_APPL.
.
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6F2S1914 (0.49)
Relay application:
GRL200 (Soft 033 & 037)