Toshiba GR200 Series Instruction Manual page 496

Abnormal currents flowing in CTs (CT error)
9.2.15
The CT supervision is to examine whether the three-phase currents are balanced and the
current in zero-sequence is minimum. It secures the operation of the CT circuits†. By
monitoring the currents flowing in the AC analog input circuits, it is also applicable to detect
the failure in the CT circuit. The failure is determined as Equation (9.2-1) is satisfied.
1.
where,
Max (|Ia|, |Ib|, |Ic|):
Min (|Ia|, |Ib|, |Ic|):
k :
0
†Note: When the VCT has two or more three-phase-CT circuits, the CT supervision may
be required to operate for respective CT circuits. The rated current above the
equation is defined with VCT setting. For more information regarding the VCT,
see Chapter
Settings are required to respective groups of the three-phase currents.
Error level
(i)
Generally, the default error level has been set at level 3 (Minor error), but the user can program
the level using settings [CHK_CT:LVl] and the others; then, set On for the setting [CHK_CT:Sw]
or whatever required. The time to detect can be programmed using [CHK_CT:Timer], etc.,
which can be set for 15 seconds as default. After the error is cleared, resetting will be performed
after the elapse of setting time.
Error message
(ii)
When detecting an error, an error message will be shown on the LCD screen and an LED is lit.
Table 9.2-30 Error messages provided by the supervisor in CHK_CT_CBP
Message and level
CTx error
Error level
Max (| I | , | I | , | I |) − 4 × Min (| I
a b c
The largest amplitude among Ia, Ib, and Ic
The smallest amplitude among Ia, Ib, and Ic
20% of the rated current†
Technical description: Transformer module for AC analog input
Meaning of the information
the extraordinary current flowing located at CTx
Minor error (Level 3)
- 482 -
| , | I | , | I |) ≥ k
a b c 0
Centralized GRB200
(Soft: 030, 031, 032, 033, 034)
6F2S1931 (0.20)
(9.2-1)
.