Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual, Page: 362 / 824

5.18
SEL-700G Relay Instruction Manual Date Code 20170814
Metering and Monitoring
Breaker Monitor
Breaker Maintenance Curve Details
In Figure 5.18, note that set points KASP1n, COSP1n and KASP3n, COSP3n
are set with breaker maintenance information from the two extremes in
Table 5.10 and Figure 5.17.
Figure 5.18 SEL-700G Breaker Maintenance Curve for a 25 kV Circuit
Breaker
In this example, set point KASP2n, COSP2n happens to be from an in-
between breaker maintenance point in the breaker maintenance information in
Table 5.10 and Figure 5.17, but it does not have to be. Set point KASP2n,
COSP2n should be set to provide the best “curve-fit” with the plotted breaker
maintenance points in Figure 5.17.
Each phase (A, B, and C) has its own breaker maintenance curve (like that in
Figure 5.19), because the separate circuit breaker interrupting contacts for
phases A, B, and C do not necessarily interrupt the same magnitude current
(depending on fault type and loading).
10,000
100%
1000
2
3
4
5
6
7
8
9
100
2
3
4
5
6
7
8
9
10
2
3
4
5
6
7
8
9
1 2 3 4 5 6 7 8 9
50 40 30 20
10 .5
Number of Close/Open Operations
kA Interrupted per Operation
KASP1n = 1.2
COSP1n =
KASP2n = 8.0
COSP2n = 150
KASP3n = 20.0
COSP3n = 12