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7.1 Trip circuit supervision
7 Application
Technical description
144
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VM55.EN005
Equation 7.1.1-2 is for the CB open situation including a 100 %
safety margin to limit the maximum temperature of the
resistor.
Equation 7.1.1-2
R
I
P
DI
2
2
P = 2*0.003^2x22000 = 0.40 W
Select the next bigger standard size, for example 0.5 W.
When the trip contacts are still closed and the CB is already
open, the resistor has to withstand much higher power
(Equation 7.1.1-3) for this short time.
Equation 7.1.1-3
R
U
P
2
max
P = 121^2/22000 = 0.67 W
A 0.5 W resistor will be enough for this short time peak power,
too. However, if the trip relay is closed for longer time than a
few seconds, a 1 W resistor should be used.
Содержание VAMP 55
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