Schweitzer Engineering Laboratories SEL-421-4, Instruction Manual

Page: 261 / 1518

5.101
Date Code 20171021 Instruction Manual SEL-421 Relay
Protection Functions
Inverse-Time Overcurrent Elements
Time-Current Operating Characteristics
NOTE:
If the relay is using a remote
data acquisition system, such as TiDL,
the operating times will be delayed by
1.5 ms. Use caution when setting the
relay coordination times to account
for this added delay.
The following information describes curve timing for time-overcurrent element
curve and time-dial settings. The time-overcurrent relay curves in
Figure 5.77
through Figure 5.86 conform to IEEE C37.112–1996 IEEE Standard Inverse-
Time Characteristic Equations for Overcurrent Relays.
Table 5.63 Selectable Inverse-Time Overcurrent Relay Word Bits
Name Description
51S1 Inverse-Time Overcurrent Element 1 pickup
51S1T Inverse-Time Overcurrent Element 1 timed out
51S1R Inverse-Time Overcurrent Element 1 reset
51S2 Inverse-Time Overcurrent Element 2 pickup
51S2T Inverse-Time Overcurrent Element 2 timed out
51S2R Inverse-Time Overcurrent Element 2 reset
51S3 Inverse-Time Overcurrent Element 3 pickup
51S3T Inverse-Time Overcurrent Element 3 timed out
51S3R Inverse-Time Overcurrent Element 3 reset
T
p
= operating time in seconds
T
r
= electromechanical induction-disk emulation reset time in sec-
onds (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 5.64 Equations Associated With U.S. Curves
Curve Type Operating Time Reset Time Figure
U1 (Moderately Inverse) Figure 5.77
U2 (Inverse) Figure 5.78
U3 (Very Inverse) Figure 5.79
U4 (Extremely Inverse) Figure 5.80
U5 (Short-Time Inverse) Figure 5.81
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 0.02434
5.64
M
2
1
–
---------------- +
 
 
• =
T
r
TD
5.64
1 M
2
–
----------------
 
 
• =
T
p
TD 0.00262
0.00342
M
0.02
1
–
-------------------- +
 
 
• =
T
r
TD
0.323
1 M
2
–
----------------
 
 
• =