Toshiba GR200 Series Instruction Manual page 1272

10.2.14 Abnormal currents flowing in CTs (CT error)
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 (10.2-1) is satisfied.
1.
where,
Max (|Ia|, |Ib|, |Ic|):
Min (|Ia|, |Ib|, |Ic|):
k :
0
†Note: When the VCT has double 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 the function operates and detects error, an error message can be shown at the LED and
the LCD screen.
Table 10.2-29 Error messages provided by the supervisor in CHK_CT
Message and level
CT error
CT2 error
Error level
Table 10.2-30 Detailed information in Hexadecimal in CHK_CT
Display area
N/A
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 the CT
the extraordinary current flowing located at the other CT2
Minor error (Level 3)
Meaning of the detailed information
(No information is displayed)
- 1249 -
| , | I | , | I |) ≥ k
a b c 0
6F2S1914 (0.49)
(10.2-1)
.
GRL200 (Soft 033 & 037)