Date Code 20020129
Differential, Restricted Earth Fault,
3-51
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
Time Overcurrent Curve Reference Information
tp = operating time in seconds
tr = electromechanical induction-disk emulation reset time in seconds
(if electromechanical reset setting is made)
TD = time-dial setting
M = applied multiples of pickup current [for operating time (tp), M>1; for reset time (tr), M
1]
U.S. Moderately Inverse Curve: U1
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
+
=
2
02
.
0
M
1
08
.
1
•
TD
tr
1
M
0104
.
0
0226
.
0
•
TD
tp
U.S. Inverse Curve: U2
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
+
=
2
2
M
1
95
.
5
•
TD
tr
1
M
95
.
5
180
.
0
•
TD
tp
U.S. Very Inverse Curve: U3
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
+
=
2
2
M
1
88
.
3
•
TD
tr
1
M
88
.
3
0963
.
0
•
TD
tp
U.S. Extremely Inverse Curve: U4
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
+
=
2
2
M
1
67
.
5
•
TD
tr
1
M
67
.
5
0352
.
0
•
TD
tp
U.S. Short-Time Inverse Curve: U5
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
+
=
2
02
.
0
M
1
323
.
0
•
TD
tr
1
M
00342
.
0
00262
.
0
•
TD
tp
I.E.C. Class A Curve (Standard Inverse): C1
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
=
2
02
.
0
M
1
5
.
13
•
TD
tr
1
M
14
.
0
•
TD
tp
I.E.C. Class B Curve (Very Inverse): C2
ß
à
Þ
Ï
Ð
Î
-
=
ßà
Þ
ÏÐ
Î
-
=
2
M
1
3
.
47
•
TD
tr
1
M
5
.
13
•
TD
tp
I.E.C. Class C Curve (Extremely Inverse): C3
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
=
2
2
M
1
0
.
80
•
TD
tr
1
M
0
.
80
•
TD
tp
I.E.C. Long-Time Inverse Curve: C4
ßà
Þ
ÏÐ
Î
-
=
ßà
Þ
ÏÐ
Î
-
=
M
1
0
.
120
•
TD
tr
1
M
0
.
120
•
TD
tp
I.E.C. Short-Time Inverse Curve: C5
ß
à
Þ
Ï
Ð
Î
-
=
ß
à
Þ
Ï
Ð
Î
-
=
2
04
.
0
M
1
85
.
4
•
TD
tr
1
M
05
.
0
•
TD
tp