Siemens siprotec 7SA522 - Time Overcurrent Protection Data

Installation and Commissioning
8-8 7SA522 Manual
C53000-G1176-C119-2
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.
Figure 8-6 Trip circuit supervision with one binary input
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 should be selected.
In order that the minimum voltage for controlling the binary input is ensured, R
max
is
derived as:
L–
L+
RTC
Aux2Aux1
U
BI
!57&6WDWXV
U
CTR
7SA522
7SA522
TC
CB
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
CTR
— Control voltage (trip voltage)
U
BI
— input voltage for Binary Input
R
R
R
max
R
min
+
2
---------------------------------=
R
max
U
CRT
U
BI min
–
I
BI (High)
--------------------------------------


R
CBTC
–
=