5 Operation
m
6000 -
Σ
(n
i
•
k
i
)
i = 1
k
x
n
x
=
1000037b
ki
Weighting factor for breaking current I
kx
Weighting factor for breaking current l
x
n.
Number of carried out interruptions at breaking current I
nx
Number of remaining permissible interruptions at breaking
current
l
x
.
Fig. 58 Formula for calculating the max. number of
permissible interruptions
The maximum number of interruptions still permissible with a given number of operations (with consequent wear)
already carried out can be calculated using the above equation.
For example:
The circuit-breaker with a rated short-circuit breaking current of 50 kA has performed 250 interruptions with
breaking currents of 3.15 kA, and 2 interruptions 20 kA.
How many interruptions at 40 kA are still permissible?
n
40
=
=
=
= 10,7
6000 - (250 + 200)
520
6000 - (n
3.15
•
k
3.15
+ n
20
•
k
20
)
k
40
60
)
520
00 - (250
•
1 + 2
•
100
Fig. 59
Number of remaining permissible interruptions
at breaking current l
x
.
A total of 10 interruptions at 40 kA are still permissible.
79
