Ct Circuit Failure Detection - Toshiba GRL100-701B Instruction Manual

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.
381:CTFID-A
382:CTFID-B
383:CTFID-C
CTFID
388:CTFUV-A
389:CTFUV-B
390:CTFUV-C
CTFUV
392:CTFUVD-A
393:CTFUVD-B
394:CTFUVD-C
CTFUVD
391:CTFOVG
CTFOVG
CTF detection
Setting
The setting elements necessary for the CTF and their setting ranges are as follows:
Element Range
CFID 0.25 - 5.00 A
( 0.05 - 1.00 A
CFUV 20 - 60 V
CFDV 1 - 10 %
CFOVG 0.1 - 10.0 V
[CTFEN] Off/On/OPT-On
[CTFCNT] NA / BLK
(*) 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
≥1
&
CTFID (CFID): Differential current element for CTF
CTFUVD (CFDV): Undervoltage change element for CTF
CTFUV (CFUV): Undervoltage element for CTF
1
CTFOVG (CFOVG): Zero-sequence overvoltage element for CTF
Figure 3.3.4.1 CTF Detection Logic
Step
0.1 A
0.01 A
1 V
1 %
0.1 V
 175 
&
1
Default Remarks
0.25 A Id current level
0.05 A) (*)
20 V
7 % % of rated voltage
1.0 V Zero-sequence voltage
Off CTF enabled or not
NA Control by CTF detection
6 F 2 S 0 8 5 0
CTF detection