Siemens siprotec 7SA522 User Manual page 464

Installation and Commissioning
8-8
If two binary inputs are used for the trip circuit supervision, these binary inputs must
be potential free i.o.w. not be commoned with each other or with another binary input.
If one binary input is used, a bypass resistor R must be employed (refer to Figure 8-
6). This resistor R is connected in series with the second circuit breaker auxiliary con-
tact (Aux2), to also allow the detection of a trip circuit failure when the circuit breaker
auxiliary contact 1 (Aux1) is open, and the command relay contact has reset. The val-
ue 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.
L+
RTC
TC Aux1
CB
L–
Figure 8-6 Trip circuit supervision with one binary input
This results in an upper limit for the resistance dimension, R
from which the optimal value of the arithmetic mean should be selected.
R + R
max min
R = ---------------------------------
2
In order that the minimum voltage for controlling the binary input is ensured, R
derived as:
U
CTR
U
BI
7SA522
R
Aux2
U U
–

CRT BI min
------------------------------------- -
R =

max
I
BI (High)
7SA522
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Legend:
RTC — Relay Tripping Contact
CB — Circuit Breaker
TC — circuit breaker Trip Coil
Aux1 — circuit breaker Auxiliary contact
(closed when CB is closed)
Aux2 — circuit breaker Auxiliary contact
(closed when CB is open)
R — bypass Resistor
U — Control voltage (trip voltage)
CTR
U — input voltage for Binary Input
BI
, and a lower limit R
max

– R

CBTC
C53000-G1176-C119-2
,
min
is
max
7SA522 Manual