Sel 751A, Instruction Manual

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5.18
SEL-751A Relay Instruction Manual Date Code 20100129
Metering and Monitoring
Breaker Monitor
Breaker Maintenance Curve Details
In Figure 5.18 , note that set points KASP1, COSP1 and KASP3, COSP3 are
set with breaker maintenance information from the two extremes in Table 5.9
and Figure 5.17 .
Figure 5.18 SEL-751A Breaker Maintenance Curve for a 25 kV Circuit
Breaker
In this example, set point KASP2, COSP2 happens to be from an in-between
breaker maintenance point in the breaker maintenance information in
Table 5.9 and Figure 5.17 , but it does not have to be. Set point KASP2,
COSP2 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 5.18 ), 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
KASP1 = 1.2
COSP1 = 10000
KASP2 = 8.0
COSP2 = 150
KASP3 = 20.0
COSP3 = 12