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3V
= residual voltage
0
−3V
= polarizing voltage
0
φ = lagging angle of (3I
θ = characteristic angle setting (lagging to polarizing voltage)
I sf , I sr = current setting
V sf , V sr = voltage setting
2.16.6 Inverse Definite Minimum Time (IDMT) Overcurrent Element OCI and EFI
As shown in Figure 2.16.6.1, the IDMT element has one long time inverse characteristic and three
inverse time characteristics in conformity with IEC 60255-3. One of these characteristics can be
selected.
Operating
time t
These characteristics are expressed by the following equations.
) to (−3V
)
0
0
(s)
200
100
50
20
10
5
2
1
0.5
0.2
0.1
1
2
5
Current I (Multiple of setting)
Figure 2.16.6.1 IDMT Characteristics
144
TD=1
Long-time Inverse
Standard Inverse
Very Inverse
Extremely Invease
10
20
30
6 F 2 S 0 8 5 0
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