Sel SEL-787 - Table 4.16 Equations Associated with U.S. Curves; Table 4.17 Equations Associated with IEC Curves

4.43
Date Code 20150130 Instruction Manual SEL-787 Relay
Protection and Logic Functions
Basic Protection
Time-Overcurrent Curves
The following information describes the curve timing for the curve and time
dial settings made for the time-overcurrent elements (see Table 4.16 and
Table 4.17). The U.S. and IEC time-overcurrent relay curves are shown in
Figure 4.25 through Figure 4.34. Curves U1, U2, and U3 (Figure 4.25 through
Figure 4.27) conform to IEEE C37.112-1996 IEEE Standard Inverse-Time
Characteristic Equations for Overcurrent Relays.
Table 4.16 Equations Associated With U.S. Curves
Curve Type Operating Time Reset Time Figure
U1 (Moderately Inverse) Figure 4.25
U2 (Inverse) Figure 4.26
U3 (Very Inverse) Figure 4.27
U4 (Extremely Inverse) Figure 4.28
U5 (Short-Time Inverse) Figure 4.29
t
p
= operating time in seconds
t
r
= electromechanical induction-disk emulation reset time in seconds (if you select electromechanical reset setting)
TD = time-dial setting
M = applied multiples of pickup current [for operating time (t
p
), M >1; for reset time (t
r
), M 1]
Table 4.17 Equations Associated With IEC Curves
Curve Type Operating Time Reset Time Figure
C1 (Standard Inverse) Figure 4.30
C2 (Very Inverse) Figure 4.31
C3 (Extremely Inverse) Figure 4.32
C4 (Long-Time Inverse) Figure 4.33
C5 (Short-Time Inverse) Figure 4.34
t
p
= operating time in seconds
t
r
= electromechanical induction-disk emulation reset time in seconds (if you select electromechanical reset setting)
TD = time-dial setting
M = applied multiples of pickup current [for operating time (t
p
), M >1; for reset time (t
r
), M 1]
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 0.0352
5.67
M
2
1–
----------------+


• =
t
r
TD
5.67
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
–
----------------


• =