Siemens SIPROTEC 7SA522 Manual page 326

2 Functions
326
Figure 2-143 Principle of the trip circuit monitoring with two binary inputs
Monitoring with two binary inputs does not only detect interruptions in the trip circuit
and loss of control voltage, it also monitors the response of the circuit breaker using
the position of the circuit breaker auxiliary contacts.
Depending on the conditions of the trip contact and the circuit breaker, the binary
inputs are activated (logical condition "H" in the following table), or short-circuited (log-
ical condition "L").
A state in which both binary inputs are not activated ("L") is only possible in intact trip
circuits for a short transition period (trip relay contact closed but circuit breaker not yet
open).
A continuous state of this condition is only possible when the trip circuit has been in-
terrupted, a short-circuit exists in the trip circuit, a loss of battery voltage occurs, or
malfunctions occur with the circuit breaker mechanism. Therefore, it is used as moni-
toring criterion.
Table 2-11 Condition Table for Binary Inputs, Depending on RTC and CB Position
No Trip contact Circuit breaker
.
1 Open ON
2 Open OFF
3 Closed ON
4 Closed OFF
The conditions of the two binary inputs are scanned periodically. A query takes place
about every 500 ms. If three consecutive conditional checks detect an abnormality, an
annunciation is reported (see Figure 2-144). The repeated measurements help to de-
termine the delay of the alarm message and to avoid that an alarm is output during
short-time transition periods. After the fault in the trip circuit is removed, the alarm is
reset automatically after the same time.
AuxCont 1 AuxCont 2
Closed Open
Open Closed
Closed Open
Open Closed
BI 1 BI 2
H L
H H
L L
L H
7SA522 Manual
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