Schweitzer Engineering Laboratories SEL-751 - Table 4.17 Equations Associated with U.S. Curves; Table 4.18 Equations Associated with IEC Curves

4.23
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
Relay Word Bit ORED51T
Relay Word bit ORED51T is asserted if any of the Relay Word bits 51AT, 51BT,
51CT, 51PIT, 51P2T, 51N1T, 51N2T, 51G1T, 51G2T, or 51QT are asserted.
Table 4.17 Equations Associated With U.S. Curves
Curve Type Operating Time Reset Time Figure
U1 (Moderately Inverse) Figure 4.10
U2 (Inverse) Figure 4.11
U3 (Very Inverse) Figure 4.12
U4 (Extremely Inverse) Figure 4.13
U5 (Short-Time Inverse) Figure 4.14
Table 4.18 Equations Associated With IEC Curves
Curve Type Operating Time Reset Time Figure
C1 (Standard Inverse) Figure 4.15
C2 (Very Inverse) Figure 4.16
C3 (Extremely Inverse) Figure 4.17
C4 (Long-Time Inverse) Figure 4.18
C5 (Short-Time Inverse) Figure 4.19
t
p
TD 0.0226
0.0104
M
0.02
1–
----------------------+


• =
t
r
TD
1.08
1 M
2
–
----------------


• =
t
p
TD 0.180
5.95
M
2
1–
----------------+


• =
t
r
TD
5.95
1 M
2
–
----------------


• =
t
p
TD 0.0963
3.88
M
2
1–
----------------+


• =
t
r
TD
3.88
1 M
2
–
----------------


• =
t
p
TD 0.0352
5.67
M
2
1–
----------------+


• =
t
r
TD
5.67
1 M
2
–
----------------


• =
t
p
TD 0.00262
0.00342
M
0.02
1–
----------------------+


• =
t
r
TD
0.323
1 M
2
–
----------------


• =
where:
t
p
=
t
r
=
TD =
M =
operating time in seconds (see Note on page 4.22)
electromechanical induction—disk emulation reset time in seconds (if you select electromechanical reset setting)
time-dial setting
applied multiples of pickup current [for operating time (t
p
), M>1; for reset time (t
r
), M1]
t
p
TD
0.14
M
0.02
1–
----------------------


• =
t
r
TD
13.5
1 M
2
–
----------------


• =
t
p
TD
13.5
M 1–
--------------


• =
t
r
TD
47.3
1 M
2
–
----------------


• =
t
p
TD
80
M
2
1–
----------------


• =
t
r
TD
80
1 M
2
–
----------------


• =
t
p
TD
120
M 1–
--------------


• =
t
r
TD
120
1 M–
--------------


• =
t
p
TD
0.05
M
0.04
1–
----------------------


• =
t
r
TD
4.85
1 M
2
–
----------------


• =
where:
t
p
=
t
r
=
TD =
M =
operating time in seconds (see Note on page 4.22)
electromechanical induction—disk emulation reset time in seconds (if you select electromechanical reset setting)
time-dial setting
applied multiples of pickup current [for operating time (t
p
), M>1; for reset time (t
r
), M1]