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Curve Description
IEC Normal Inverse
IEC Very Inverse
IEC Extremely Inverse
UK Long Time Inverse
IEEE Moderately Inverse
IEEE Very Inverse
IEEE Extremely Inverse
US CO8 Inverse
US CO2 Short Time Inverse
User configurable curve
Note: kr and β are used to define the reset characteristic. Refer to equation (2).
2.1.2
Definite Time Overcurrent Protection
In a system in which the fault current does not vary a great deal in relation to the position of the
fault, that is, the impedance between the relay and the power source is large, the advantages of the
Table 2.1.1 Specification of IDMT Curves
IEC ref.
k
A
0.14
B
13.5
C
80
-
120
D
0.0515
E
19.61
F
28.2
-
5.95
-
0.02394
-
0.00 –
300.00
IEEE Reset Curves
(Time Multiplier = 1)
1000.00
100.00
EI
VI
10.00
CO8
MI
CO2
1.00
0.1
Current (Multiple of Setting)
Figure 2.1.3 Dependent Time Reset Characteristics
11
c
k
α
r
0.02
0
-
1
0
-
2
0
-
1
0
-
0.02
0.114
4.85
2
0.491
21.6
2
0.1217
29.1
2
0.18
5.95
0.02
0.01694
2.261
0.00 –
0.000 –
0.00 –
5.00
5.000
300.00
1
6 F 2 T 0 1 7 2
β
-
-
-
-
2
2
2
2
2
0.00 –
5.00
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