Toshiba GR200 Series Instruction Manual page 52

CT circuit failure detection (Open circuit)
2.1.8
If a failure (open-circuit) occurs in a CT circuit, the DIF elements may operate incorrectly.
Therefore, CT circuit failure detection is provided in the DIF function. The DIF function
determines that a failure has occurred in the CT circuit when the following two criteria are
observed: (i) the differential current (Id) is introduced and (ii) the voltage changes are not
observed.
To operate the CTF detection function, the user should set scheme switch [CTF-EN] On.
Consequently if a CT circuit failure is detected in the respective protection-zones (DIFCH and
DIFZA to DIFZF), the DIF operation can be blocked. The information of the CTF detection is
transferred to the automatic supervision function (See Chapter
function
).
Detection of the differential current
(i)
Figure 1.1-14 shows the CTF logic; the DIF-CTF relay in each protection-zone is used to
monitor the differential current. If a differential current (Id) is observed, each DIF-CTF
element will operate. Setting [DIF-CTF] is provided to configure the detection level.
Observation of the voltage-being-unchanged
(ii)
The voltage relays (UVDCTF and UVCTF) are used to monitor the voltage in each protection-
zone. The outputs from the UVDCTF and UVCTF relay are used to confirm that a power
system fault has occurred, as shown in Figure 1.1-14. Thereby, the absence of a voltage change
is included in the criterion for CTF detection. Settings [UVD-CTF] and [UV-CTF] are provided
to configure the detection level of the voltage-change.
Introduction of external CT circuit failure detection and blocking CT
(iii)
failure detection function by PLC signal
As mentioned above, a failure in the CT circuit can induce a mal-operation in the DIF function.
If the user wishes to use a signal provided by an external CT circuit failure detection function†
to prevent mal-operation of the DIF function for the detection of a CT circuit failure, the user
can utilize the external signal using PLC connection point "EXTERNAL CTF".
On the other hand, a PLC connection point "CTF_BLOCK" is also provided when the user
wishes to disable the CT circuit failure detection function. To disable the CTF function, the
user should connect a signal to "CTF_BLOCK" using the PLC function.
†Note: The external CT circuit failure detection function is assumed to be a
device/function outside the GRB200. The user can connect the DIF function with
the outside signal using the PLC function.
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6F2S1931 (0.20)
Automatic supervision
Centralized GRB200
(Soft: 030, 031, 032, 033, 034)