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3 Mounting and Commissioning
210
7ST6 Manual
E50417-G1176-C251-A3
breaker auxiliary contact (Aux1) is open and the trip contact has dropped out. The
value of this resistor must be such that in the circuit breaker open condition (therefore
Aux1 is open and Aux2 is closed) the circuit breaker trip coil (TC) is no longer picked
up and binary input (BI1) is still picked up if the command relay contact is open.
Figure 3-2
Trip circuit supervision with one binary input – example for trip circuit
This results in an upper limit for the resistance dimension, R
max
, and a lower limit R
min
,
from which the optimal value of the arithmetic mean R should be selected:
In order that the minimum voltage for controlling the binary input is ensured, R
max
is
derived as:
So the circuit breaker trip coil does not remain energized in the above case, R
min
is
derived as:
If the calculation yields that R
max
< R
min
, then the calculation must be repeated using
the next lowest switching threshold U
BI min
, and this threshold must be implemented in
the relay using plug-in jumpers (see Section „Hardware Modifications“).
I
BI (HIGH)
Constant current with activated BI (= 1.8 mA)
U
BI min
Minimum control voltage for BI (=19 V for delivery setting for nominal
voltage of 24/48/60 V; 88 V for delivery setting for nominal voltage of
110/125/220/250 V)
U
CTR
Control voltage for trip circuit
R
TC
DC resistance of circuit breaker trip coil
U
TC (LOW)
Maximum voltage on the circuit breaker trip coil that does not lead to trip-
ping
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