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CTF features
2.21.1
The CTF function has two relay elements in order to decide the failure in the CT; hence, two
criterions exist to detect the failure in the CT in the CTF function.
Earth fault overcurrent element (EFCTF)
(i)
The earth fault overcurrent element (EFCTF) monitors the zero-sequence current for the
failure in the CT. The threshold of the EFCTF element is set using the [EFCTF].
Earth fault overvoltage element (OVGCTF)
(ii)
The earth fault overvoltage element (OVGCTF) monitors the zero-sequence voltage for the
failure in the CT. The OVGCTF element is set using the [OVGCTF].
Detection criterion (CTF_DETECT)
(iii)
When the EFCTF element operates whereas the OVGCTF element does not operate, the
detection criterion (CTF_DETECT) is applied.
Operation for the CTF function
2.21.2
When the CTF function detects the failure, issuing the CTF_DETECT signal is continuing
regardless of the operation of the OVGCTF relay, provided On is set for the scheme switch
[CTF-EN]. Issuing the CTF _DETECT is continued until the operation of the EFCTF relay is
reset.
However, nonetheless the OVGCTF relay is still running after the CTF detection, issuing
the CTF_DETECT signal is cleared, provided OPT-On is set for the scheme switch [CTF-EN].
When issuing the CTF_DETECT signal continues longer than ten seconds, the signal
CTF_DETECT clears to generate the CTF_ALARM signal.
Scheme logic
2.21.3
Figure 2.21-1 shows the logic of the CTF function. CTF_DET signal is issued when the EFCTF
element is running and the OVGCTF element is not running.
- 228 -
6F2T0207 (0.01)
GRE200 (5,6)
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