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3.5 Circuit breaker condition
monitoring
3 Supporting functions
Technical description
120
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VM50.EN004
Clearing "operations left" counters
After the breaker curve table is filled and the alarm currents
are defined, the wearing function can be initialised by clearing
the decreasing operation counters with parameter "Clear"
(Clear oper. left cntrs). After clearing the relay will show the
maximum allowed operations for the defined alarm current
levels.
Operation counters to monitor the wearing
The operations left can be read from the counters "Al1Ln"
(Alarm 1) and "Al2Ln" (Alarm2). There are three values for
both alarms, one for each phase. The smallest of three is
supervised by the two alarm functions.
Logarithmic interpolation
The permitted number of operations for currents in between
the defined points are logarithmically interpolated using
equation
Equation 3.5-1
n
I
a
C
,
where
C = permitted operations
I = interrupted current
a = constant according Equation 3.5-2
n = constant according Equation 3.5-3
Equation 3.5-2
k
k
k
k
I
I
C
C
n
1
1
ln
ln
Equation 3.5-3
2
k
k
I
C
a
ln = natural logarithm function
C
k
= permitted operations.
k = row 2...7 in Table 3.5-1.
I
k
= corresponding current.
k = row 2...7 in Table 3.5-1.
C
k+1
= permitted operations.
k = row 2...7 in Table 3.5-1.
I
k+1
= corresponding current.
k = row 2...7 in Table 3.5-1.