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10.2.15 Abnormal currents flowing in CTs (CT error)
CT supervision is to examine in order that three-phase currents are balanced and the current
in zero-sequence is minimum. The CT supervision can secure the operation of the CT circuits†.
By monitoring the currents flowing on analog input circuits, it is also applicable to detect a
failure on CT circuit. The failure will be determined when Equation (10.2-1) is verified.
1.
where,
Max (|Ia|, |Ib|, |Ic|):
Min (|Ia|, |Ib|, |Ic|):
k
:
0
†Note: rated current is defined by the ordering code. See Chapter
Rated frequency and rated current
Error level
(i)
Error level has been set at level 3 (Minor error; default), but the user can change it with setting
[CHK_CT:LVl]. Remember that the user needs to set On for setting [CHK_CT:Sw]. The time for
detection can be set with [CHK_CT:Timer], but it has been set for default 15 seconds. When it
is cleared, resetting error will be carried out after the elapse of the setting [CHK_CT:Timer].
Error message
(ii)
When detecting an error, the error message will be shown on the LCD screen. LED will be lit
up.
Table 10.2-29 Error messages provided by the supervisor in CHK_CT
Message and level
CT error
Error level
Table 10.2-30 Detailed information in Hexadecimal in CHK_CT
Display
area
Top
00000001: CT error is existing
row
Middle
Calculated Min (| I
row
Bottom
(No information is displayed)
row
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†
the extraordinary current flowing located at CT
Minor error (Level 3)
Meaning of the detailed information
Left column
|) value
| , | I
| , | I
a
b
c
- 816 -
| , | I
| , | I
|) ≥ k
a
b
c
(→p. 627).
Meaning of the information
Calculated Max (| I
(No information is displayed)
(No information is displayed)
6F2T0207 (0.01)
(10.2-1)
0
Technical description:
Right column
| , | I
| , | I
|) value
a
b
c
GRE200 (5,6)
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