Sel 751A, Instruction Manual

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5.22
SEL-751A Relay Instruction Manual Date Code 20100129
Metering and Monitoring
Breaker Monitor
25 Percent to 50 Percent Breaker Wear
Refer to Figure 5.22 . The current value changes from 2.5 kA to 12.0 kA. 12.0
kA is interrupted 11 times (11 close/open operations = 24 – 13), pushing the
breaker maintenance curve from the 25 percent wear level to the 50 percent
wear level.
Compare the 100 percent and 50 percent curves and note that for a given
current value, the 50 percent curve has only 1/2 of the close/open operations
of the 100 percent curve.
Figure 5.22 Breaker Monitor Accumulates 50 Percent Wear
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
25%
50%