The directional coefficient is calculated according to the formula:
Directional Coef
B
A
I
I
f
r
=
= −
log
log
.2 2609
A070794 V2 EN (Equation 79)
I
r
Rated operating current = 630 A
I
f
Rated fault current = 16 kA
A Op number rated = 30000
B Op number fault = 20
Calculation for estimating the remaining life
The equation shows that there are 30,000 possible operations at the rated operating
current of 630 A and 20 operations at the rated fault current 16 kA. Therefore, if the
tripping current is 10 kA, one operation at 10 kA is equivalent to 30,000/500=60
operations at the rated current. It is also assumed that prior to this tripping, the
remaining life of the circuit breaker is 15,000 operations. Therefore, after one
operation of 10 kA, the remaining life of the circuit breaker is 15,000-60=14,940 at the
rated operating current.
Spring charging time indication
For normal circuit breaker operation, the circuit breaker spring should be charged
within a specified time. Therefore, detecting long spring charging time indicates the
time for circuit breaker maintenance. The last value of the spring charging time can be
given as a service value.
Gas pressure supervision
The gas pressure supervision monitors the gas pressure inside the arc chamber. When
the pressure becomes too low compared to the required value, the circuit breaker
operations are locked. A binary input is available based on the pressure levels in the
function, and alarms are generated based on these inputs.
1MRK 505 291-UEN A Section 12
Monitoring
281
Application manual
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