Technical description
7 Application
7.1 Trip circuit supervision
VM55.EN005
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143
Figure 7.1.1-4 An example of output matrix configuration for trip circuit
supervision with one digital input.
Example of dimensioning the external resistor R
:
U
aux
= 110 Vdc –20 % + 10%
Auxiliary voltage with tolerance
U
DI
= 18 Vdc
Threshold voltage of the digital input
I
DI
= 3 mA
Typical current needed to activate the digital input
including a 1 mA safety margin.
P
coil
= 50 W
Rated power of the open coil of the circuit breaker. If
this value is not known, 0
can be used for the R
coil
.
U
min
= U
aux
– 20 % = 88 V
U
max
= U
aux
+ 10 % = 121 V
R
coil
= U
2aux
/P = 242
.
The external resistance value is calculated using Equation
7.1.1-1.
Equation 7.1.1-1
DI
coil
DI
DI
I
R
I
U
U
R
min
R = (88 – 18 – 0.003*242)/0.003 = 23.1 k
(In practice the coil resistance has no effect.)
By selecting the next smaller standard size we get 22 k
.
The power rating for the external resistor is estimated using
Equation 7.1.1-2 and Equation 7.1.1-3. The
