Sel 751A, Instruction Manual

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5.20
SEL-751A Relay Instruction Manual Date Code 20100129
Metering and Monitoring
Breaker Monitor
Note in the following four figures ( Figure 5.20 – Figure 5.23 ) that the
interrupted current in a given figure is the same magnitude for all the
interruptions (e.g., in
Figure 5.21 , 2.5 kA is interrupted 290 times). This is not
realistic, but helps in demonstrating the operation of the breaker maintenance
curve and how it integrates for varying current levels.
0 Percent to 10 Percent Breaker Wear
Refer to Figure 5.20 . 7.0 kA is interrupted 20 times (20 close/open operations
= 20 – 0), pushing the breaker maintenance curve from the 0 percent wear
level to the 10 percent wear level.
Compare the 100 percent and 10 percent curves and note that for a given
current value, the 10 percent curve has only 1/10 of the close/open operations
of the 100 percent curve.
Figure 5.20 Breaker Monitor Accumulates 10 Percent Wear
10,000
100%
10%
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