Section 6 1MAC309294-MB F
Condition monitoring functions
370 RER620
Technical Manual
Figure 203: Trip Curves for a typical 12 kV, 630 A, 16 kA vacuum interrupter
Nr the number of closing-opening operations allowed for the circuit breaker
Ia the current at the time of tripping of the circuit breaker
Calculation of Directional Coefficient
The directional coefficient is calculated according to the formula:
(Equation 42)
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
Directional Coef
B
A
I
I
f
r
=
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
=−
log
log
.2 2609
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