Schweitzer Engineering Laboratories SEL-351A - Time-Overcurrent Curves; Table 9.3 Equations Associated with U.S. Curves; Table 9.4 Equations Associated with IEC Curves

9.4
SEL-351A Relay Instruction Manual Date Code 20080213
Setting the Relay
Time-Overcurrent Curves
Time-Overcurrent Curves
The following information describes the curve timing for the curve and time
dial settings made for the time-overcurrent elements (see Figure 3.14–
Figure 3.21). The time-overcurrent relay curves in Figure 9.1–Figure 9.10
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 9.3 Equations Associated With U.S. Curves
Curve Type Operating Time Reset Time Figure
U1 (Moderately Inverse) Figure 9.1
U2 (Inverse)
Figure 9.2
U3 (Very Inverse) Figure 9.3
U4 (Extremely Inverse)
Figure 9.4
U5 (Short-Time Inverse) Figure 9.5
Table 9.4 Equations Associated With IEC Curves (Sheet 1 of 2)
Curve Type Operating Time Reset Time Figure
C1 (Standard Inverse) Figure 9.6
C2 (Very Inverse)
Figure 9.7
C3 (Extremely Inverse)
Figure 9.8
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
–()
---------------------
⎝⎠
⎛⎞
• =
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