Schweitzer Engineering SEL-387-0 - Time-Overcurrent Curves; Table 3.5 Equations Associated with U.S. Curves; Table 3.6 Equations Associated with IEC Curves

3.66
SEL-387-0, -5, -6 Relay Instruction Manual Date Code 20170601
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Time-Overcurrent Curves
Time-Overcurrent Curves
Standard Inverse-
Time Characteristic
Curves
The information in Table 3.5 and Table 3.6 describes the curve timing for the
curve and time dial settings made for the time-overcurrent elements. The time-
overcurrent curves in Figure 3.28 through Figure 3.37 conform to IEEE
C37.112-1996 IEEE Standard Inverse-Time Characteristic Equations for
Overcurrent Relays.
Where:
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 3.5 Equations Associated With U.S. Curves
Curve Type Operating Time Reset Time Figure
U1 (Moderately Inverse) Figure 3.28
U2 (Inverse)
Figure 3.29
U3 (Very Inverse)
Figure 3.30
U4 (Extremely Inverse)
Figure 3.31
U5 (Short-Time Inverse)
Figure 3.32
Table 3.6 Equations Associated With IEC Curves (Sheet 1 of 2)
Curve Type Operating Time Reset Time Figure
C1 (Standard Inverse) Figure 3.33
C2 (Very Inverse)
Figure 3.34
C3 (Extremely Inverse)
Figure 3.35
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
–
----------------


• =