175
6
F
2
S
0
8
5
0
3.3.4 CT Circuit Failure Detection
If a failure occurs in a CT circuit, the differential elements may operate incorrectly. GRL100
incorporates a CT failure detection function (CTF) against such incorrect operation. When the
CTF detects a CT circuit failure, it can block the DIF trip.
The CTF is enabled or disabled by the scheme switch [CTFEN] as follows:
-
“Off”: Disabled.
-
“On”: Enabled. If once CTF is detected, the CTF function cannot be reset until ID is
reset.
-
“OPT-On”: Enabled. After CTF is detected, the CTF function is reset if CTFUV,
CTFDV or CTFOVG operates.
The DIF trip is blocked or not by the scheme switch [CTFCNT].
-
“NA”: No block the DIF trip
-
“BLK”: Block the DIF trip
Detection logic
Figure 3.3.4.1 shows the CTF detection logic.
&
CTFID
CTFUV
CTFUVD
CTFOVG
1
≥
1
CTF detection
391:CTFOVG
392:CTFUVD-A
393:CTFUVD-B
394:CTFUVD-C
&
381:CTFID-A
382:CTFID-B
383:CTFID-C
388:CTFUV-A
389:CTFUV-B
390:CTFUV-C
1
CTF detection
CTFID (CFID): Differential current element for CTF
CTFUVD (CFDV): Undervoltage change element for CTF
CTFUV (CFUV): Undervoltage element for CTF
CTFOVG (CFOVG): Zero-sequence overvoltage element for CTF
Figure 3.3.4.1 CTF Detection Logic
Setting
The setting elements necessary for the CTF and their setting ranges are as follows:
Element Range
Step Default Remarks
CFID
0.25 - 5.00 A
0.1 A
0.25 A
Id current level
( 0.05 - 1.00 A
0.01 A
0.05 A) (*)
CFUV
20 - 60 V
1 V
20 V
CFDV
1 - 10 %
1 %
7 %
% of rated voltage
CFOVG
0.1 - 10.0 V
0.1 V
1.0 V
Zero-sequence voltage
[CTFEN]
Off/On/OPT-On
Off
CTF enabled or not
[CTFCNT]
NA / BLK
NA
Control by CTF detection
(*) Current values shown in the parentheses are in the case of 1 A rating. Other current values are in
the case of 5 A rating.
3.3.5 Voltage Transformer Failure Supervision
When a fault occurs in the secondary circuit of the voltage transformer (VT), the voltage
dependent measuring elements may operate incorrectly. GRL100 incorporates a VT failure
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