Siemens SIPROTEC 7SJ62 Instruction Manual page 298

Functions
Monitoring with
One Binary Input
6-158
tion is delayed by a fixed amount of time. For two binary inputs, the delay is about 2
seconds, and for one binary input, the delay is about 300 ms. This ensures that, for
the longest possible duration of a trip signal, a false malfunction message will not be
generated.
NOTE: When using only one binary input (BI) for the trip circuit monitor, some mal-
functions, such as interruption of the trip circuit or loss of battery voltage, can indeed
be detected, but malfunctions with closed trip contacts cannot. Therefore, the mea-
surement must take place over a period of time that bridges the longest possible du-
ration of a closed trip contact. This is ensured by the fixed number of measurement
repetitions and the time between the condition checks.
When using only one binary input, a resistor R is inserted into the circuit on the system
side, instead of the missing second binary input. Through appropriate sizing of the re-
sistor and depending on the system relationship, a lower control voltage can often be
sufficient. The resistor R is inserted into the circuit of the 52b circuit breaker auxiliary
contact, to facilitate the detection of a malfunction when the 52a circuit breaker auxil-
iary contact open and the trip contact has dropped out (see Figure 6-66). This resistor
must be sized such that the circuit breaker trip coil is no longer energized when the
circuit breaker is open (which means 52a is open and 52b is closed). The binary input
should still be picked up when the trip contact is simultaneously opened.
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:
V – V

St BI min
-------------------------------- -
R =

max
I
BI (High)
So the circuit breaker trip coil does not remain energized in the above case, R
derived as:
V –

St
⋅
------------------------------------------------ -
R = R

min CBTC
V
I Constant Current with BI on
BI (HIGH)
V Minimum Control Voltage for BI (=19 V for delivery setting for nominal voltage of 24/
BI min
48/60 V;
=88 V for delivery setting for nominal voltage of 110/125/220/250 V)
V Control Voltage for Trip Circuit
ST
R DC Resistance of Circuit Breaker Trip Coil
CBTC
V Maximum Voltage on the Circuit Breaker Trip Coil that does not lead to Tripping
CBTC (LOW)
If the calculation results that R
the next lowest pickup threshold V
the device using plug-in bridges (see Subsection 8.1.3).
For the power consumption of the resistance:
V

2
St
⋅
I R --------------------------- -
P = =

R
R + R
CBTC

R
–

CBTC
V

CBTC (LOW)

CBTC (LOW)
< R , then the calculation must be repeated, with
max min
, and this threshold must be implemented in
BI min
2

⋅
R

, and a lower limit R
max min
is
max
is
min
7SJ62 Manual
C53000-G1140-C121-1
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