3 Mounting and Commissioning
268
7SD610 Manual
C53000-G1176-C145-4
Trip Circuit Moni-
toring
It must be noted that two binary inputs or one binary input and one substitute resistor
R must be connected in series. The pickup threshold of the binary inputs must there-
fore be substantially below half
the rated control DC voltage.
If two binary inputs are used for the trip circuit supervision, these binary inputs must
be isolated, i.o.w. not be communed with each other or with another binary input.
If one binary input is used, a bypass resistor R must be used (refer to Figure 2-92).
The resistor R is inserted into the circuit of the second circuit breaker auxiliary contact
(Aux2), to facilitate the detection of a malfunction also when the first circuit 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 Principle of the trip circuit supervision with one binary input
TR Trip relay contact
CB Circuit breaker
TC Circuit breaker trip coil
Aux1 Circuit breaker auxiliary contact (NC contact)
Aux2 Circuit breaker auxiliary contact (NO contact)
U-CTR Control voltage for trip circuit
U-BI Input voltage of binary input
R Equivalent resistor
UR Voltage across the equivalent resistor
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:
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