Functions
2.14 Monitoring Functions
SIPROTEC, 7SD80, Manual
E50417-G1140-C474-A1, Release date 09.2011
180
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 faulted (logical condition „L“).
A state in which both binary inputs are not activated („L“) is only possible in intact trip circuits for a short tran-
sition 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 interrupted, a fault exists in
the trip circuit, a loss of battery voltage occurs, or malfunctions occur with the circuit-breaker mechanism.
Therefore, it is used as monitoring criterion.
Table 2-5
Condition Table for Binary Inputs, Depending on RTC and CB Position
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 2-74). The
repeated measurements help to determine 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.
Figure 2-74
Logic diagram of the trip circuit monitoring with two binary inputs
Monitoring with One Binary Input
The binary input is connected in parallel to the respective command relay contact of the protection device ac-
cording to Figure 2-75. The circuit-breaker auxiliary contact is bridged with a high-ohm substitute resistor R.
The control voltage for the circuit breaker should be at least twice as high as the minimum voltage drop at the
binary input (V
Ctrl
> 2·V
BImin
). Since at least 19 V are necessary at the binary input, this supervision can be used
with a system control voltage higher than 38 V.
A calculation example for the resistance shunt R is shown in the configuration notes in Section „Mounting and
Connections“, margin „Trip Circuit Supervision“.
No
.
Command relay
Circuit breaker
52a contact 52b contact BI 1
BI 2 Dynamic state
Static state
1
Open
ON
Closed
Open
H
L
Normal operation with circuit
breaker closed
2
Open
OFF
Open
Closed
H
H
Normal operation with circuit
breaker open
3
Closed
ON
Closed
Open
L
L
Transition or
disturbance
Disturbance
4
Closed
OFF
Open
Closed
L
H
The command relay has success-
fully
activated the circuit breaker.
