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REF 610
4.1.5.
62
Feeder Protection Relay
Technical Reference Manual
Trip-circuit supervision
The trip-circuit supervision (TCS) detects open circuits, both when the circuit
breaker is open and closed, and trip-circuit supply failure.
The trip-circuit supervision is based on the constant current injection principle: by
applying an external voltage, a constant current is forced to flow through the
external trip circuit. If the resistance of the trip circuit exceeds a certain limit, due to
oxidation or a bad contact, for instance, the trip-circuit supervision will be activated
and a warning will appear on the LCD together with a fault code. The warning signal
from the trip-circuit supervision can also be routed to SO2 by setting switch SGF1/
8 to 1.
Under normal operating conditions, the applied external voltage is divided between
the relay's internal circuit and the external trip circuit so that at least 20 V remains
over the relay's internal circuit. If the external trip circuit's resistance is too high or
the internal circuit's too low, due to welded relay contacts, for instance, the voltage
over the relay's internal circuit will fall below 20 V (15...20 V), which will activate
the trip-circuit supervision.
The operation condition is:
(
U
–
R
+
R
+
R
c
ext
int
s
where
• U
= operating voltage over the supervised trip circuit
c
• I
= current flowing through the trip circuit, ~1.5 mA
c
• R
= external shunt resistor
ext
• R
= internal shunt resistor, 1 k
int
• R
= trip coil resistance
s
The external shunt resistor is used to enable trip-circuit supervision also when the
circuit breaker is open.
The resistance of the external shunt resistor is to be calculated so that it does not
cause malfunction of the trip-circuit supervision or affect the operation of the trip
coil. Too high a resistance will cause too high a voltage drop, which in turn will
result in the operation conditions not being fulfilled, whereas too low a resistance
may cause faulty operation of the trip coil.
The following values are recommended for the external resistor, R
Table 4.1.5-1
Recommended values for R
Operating voltage, U
c
48 V dc
60 V dc
110 V dc
220 V dc
The circuit breaker is to be provided with two external contacts, one opening and one
closing contact. The closing contact is to be connected in parallel with the external
shunt resistor, which will enable trip-circuit supervision when the circuit breaker is
) I
×
≥
⁄
20Vac dc
c
Ω
ext
Shunt resistor R
ext
,
1.2 kΩ
5 W
,
5.6 kΩ
5 W
,
22 kΩ
5 W
,
33 kΩ
5 W
1MRS 755310
:
ext
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