Schweitzer Engineering Laboratories SEL-421-4 - Table 5.65 Equations Associated with IEC Curves

5.102
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Functions
Inverse-Time Overcurrent Elements
Table 5.65 Equations Associated With IEC Curves
Curve Type Operating Time Reset Time Figure
C1 (Standard Inverse) Figure 5.82
C2 (Very Inverse)
Figure 5.83
C3 (Extremely Inverse)
Figure 5.84
C4 (Long-Time Inverse)
Figure 5.85
C5 (Short-Time Inverse)
Figure 5.86
T
p
TD
0.14
M
0.02
1–
--------------------


• =
T
r
TD
13.5
1M
2
–
----------------


• =
T
p
TD
13.5
M1–
--------------


• =
T
r
TD
47.3
1M
2
–
----------------


• =
T
p
TD
80
M
2
1–
----------------


• =
T
r
TD
80
1M
2
–
----------------


• =
T
p
TD
120
M1–
--------------


• =
T
r
TD
120
1M–
--------------


• =
T
p
TD
0.05
M
0.04
1–
--------------------


• =
T
r
TD
4.85
1M
2
–
----------------


• =