Sel SEL-421 - Equations Associated with U.S. Curves; Equations Associated with IEC Curves

R.1.73
Date Code 20111215 Reference Manual SEL-421 Relay
Protection Functions
Inverse-Time Overcurrent Elements
Table 1.59 Equations Associated With U.S. Curves
Curve Type Operating Time Reset Time Figure
U1 (Moderately Inverse) Figure 1.48
U2 (Inverse)
Figure 1.49
U3 (Very Inverse)
Figure 1.50
U4 (Extremely Inverse)
Figure 1.51
U5 (Short-Time Inverse)
Figure 1.52
Table 1.60 Equations Associated With IEC Curves
Curve Type Operating Time Reset Time Figure
C1 (Standard Inverse) Figure 1.53
C2 (Very Inverse)
Figure 1.54
C3 (Extremely Inverse)
Figure 1.55
C4 (Long-Time Inverse)
Figure 1.56
C5 (Short-Time Inverse)
Figure 1.57
T
p
TD 0.0226
0.0104
M
0.02
1–
----------------------+


• =
T
r
TD
1.08
1M
2
–
----------------


• =
T
p
TD 0.180
5.95
M
2
1–
----------------+


• =
T
r
TD
5.95
1M
2
–
----------------


• =
T
p
TD 0.0963
3.88
M
2
1–
----------------+


• =
T
r
TD
3.88
1M
2
–
----------------


• =
T
p
TD 0.02434
5.64
M
2
1–
----------------+


• =
T
r
TD
5.64
1M
2
–
----------------


• =
T
p
TD 0.00262
0.00342
M
0.02
1–
----------------------+


• =
T
r
TD
0.323
1M
2
–
----------------


• =
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
–
----------------


• =