VAMP 265 - Page 173

Technical description
7 Applications
7.9 Trip Circuit Supervision
VM265.EN011
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173
Figure 7.9.1-4 An example of output matrix configuration for trip circuit
supervision with one dry 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
2
aux
/P = 242 .
The external resistance value is calculated using Equation
7.9.1-1
Equation 7.9.1-1
DI
coi lDIDI
I
RIUU
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 7.9.1-2 and Equation 7.9.1-3. The Equation 7.9.1-2 is
for the CB open situation including a 100 % safety margin to
limit the maximum temperature of the resistor.
Equation 7.9.1-2