Toshiba GR200 Series Instruction Manual

Also see for GRB200: Instruction manual

6F2S1931 (0.20)Centralized GRB200(Soft: 030, 031, 032, 033, 034)- 38 -2.1.8 CT circuit failure detection (Open circuit)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 functiondetermines that a failure has occurred in the CT circuit when the following two criteria areobserved: (i) the differential current (Id) is introduced and (ii) the voltage changes are notobserved.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 andDIFZA to DIFZF), the DIF operation can be blocked. The information of the CTF detection istransferred to the automatic supervision function (See ChapterAutomatic supervisionfunction).(i) Detection of the differential currentFigure 1.1-14 shows the CTF logic; the DIF-CTF relay in each protection-zone is used tomonitor the differential current. If a differential current (Id) is observed, each DIF-CTFelement will operate. Setting [DIF-CTF] is provided to configure the detection level.(ii) Observation of the voltage-being-unchangedThe 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 powersystem fault has occurred, as shown in Figure 1.1-14. Thereby, the absence of a voltage changeis included in the criterion for CTF detection. Settings [UVD-CTF] and [UV-CTF] are providedto configure the detection level of the voltage-change.(iii) Introduction of external CT circuit failure detection and blocking CTfailure detection function by PLC signalAs 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 usercan 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 userwishes to disable the CT circuit failure detection function. To disable the CTF function, theuser should connect a signal to “CTF_BLOCK” using the PLC function.†Note:The external CT circuit failure detection function is assumed to be adevice/function outside the GRB200. The user can connect the DIF function withthe outside signal using the PLC function.