Technical description
3 Supporting functions
3.5 Circuit breaker condition
monitoring
VM59.EN001
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117
5038
.
1
1250
31000
ln
80
10000
ln
n
6
5038
.
1
10
454
1250
10000
a
Using Equation 3.5-1 the relay gets the number of permitted
operations for current 6 kA.
945
6000
10
454
5038
.
1
6
C
Thus the maximum number of current breaking at 6 kA is 945.
This can be verified with the original breaker curve in Figure
3-2. Indeed, the figure shows that at 6 kA the operation count
is between 900 and 1000. A useful alarm level for operation-
left, could be in this case for example 50 being about five per
cent of the maximum.
Example of operation counter decrementing when the CB is
breaking a current
Alarm2 is set to 6 kA. CBFP is supervising trip relay T1 and
trip signal of an overcurrent stage detecting a two phase fault
is connected to this trip relay T1. The interrupted phase
currents are 12.5 kA, 12.5 kA and 1.5 kA. How much are
Alarm2 counters decremented?
Using Equation 3.5-1 and values n and a from the previous
example, the relay gets the number of permitted operation at
10 kA.
313
12500
10
454
5038
.
1
6
10
kA
C
At alarm level 2, 6 kA, the corresponding number of operations
is calculated according
Equation 3.5-4
C
C
AlarmMax
3
313
945
2
1
L
L
Thus Alarm2 counters for phases L1 and L2 are decremented
by 3. In phase L1 the currents is less than the alarm limit
current 6 kA. For such currents the decrement is one.
1
3
L
