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4-12
Supporting Functions
Circuit Breaker Condition
Monitoring
857-UM001A-EN-P – July 2009
The device has a condition monitoring function that supervises
the wearing of the circuit-breaker. The condition monitoring can
give alarm for the need of CB maintenance well before the CB
condition is critical.
The CB wear function measures the breaking current of each CB
pole separately and then estimates the wearing of the CB
accordingly the permissible cycle diagram. The breaking current
is registered when the trip relay supervised by the circuit breaker
failure protection (CBFP) is activated. (See "Circuit Breaker
Failure Protection CBFP in Chapter 3 and the setting parameter
"CBrelay".)
Breaker Curve and its Approximation
The permissible cycle diagram is usually available in the
documentation of the CB manufacturer (Figure 4.4). The
diagram specifies the permissible number of cycles for every
level of the breaking current. This diagram is parameterized to
the condition monitoring function with maximum eight [current,
cycles] points. See Table 4.13. If less than eight points needed,
the unused points are set to [I
maximum breaking capacity.
If the CB wearing characteristics or part of it is a straight line on
a log/log graph, the two end points are enough to define that part
of the characteristics. This is because the device is using
logarithmic interpolation for any current values falling in
between the given current points 2...8.
The points 4...8 are not needed for the CB in Figure 4.4. Thus
they are set to 100 kA and one operation in the table to be
discarded by the algorithm.
100000
10000
1000
100
50
20
10
100
200
500 1000
Figure 4.4 – Example of a circuit breaker wearing characteristic graph
, 1], where I
BIG
BIG
10000
100000
Breaked current (A)
CBWEARcharacteristics
is more than the
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