3.72
SEL-387-0, -5, -6 Relay
Instruction Manual
Date Code 20050919
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Time-Overcurrent Curves
Time-Overcurrent Curves
Standard Inverse-
Time Characteristic
Curves
The information in
and
describes the curve timing for the
curve and time dial settings made for the time-overcurrent elements. The time-
overcurrent curves in
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)
U2 (Inverse)
U3 (Very Inverse)
U4 (Extremely Inverse)
U5 (Short-Time Inverse)
Table 3.6
Equations Associated with IEC Curves
(Sheet 1 of 2)
Curve Type
Operating Time
Reset Time
Figure
C1 (Standard Inverse)
C2 (Very Inverse)
C3 (Extremely Inverse)
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
–
----------------
⎝
⎠
⎛
⎞
•
=
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
–
----------------
⎝
⎠
⎛
⎞
•
=
Summary of Contents for SEL-387-0
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