ABB REL650 Applications Manual page 291

1MRK 506 334-UUS A
Application manual
in the protection IED monitors the healthy auxiliary relay coil, not the circuit breaker coil.
The separate trip circuit monitoring relay is applicable for this to supervise the trip coil of
the circuit breaker.
Dimensioning of the external resistor
Under normal operating conditions, the applied external voltage is divided between the
relay's internal circuit and the external trip circuit so that at the minimum 20V (3...20 V)
remains over the relay's internal circuit. Should the external circuit's resistance be too
high or the internal circuit's too low, for example due to welded relay contacts, the fault
is detected.
Mathematically, the operation condition can be expressed as:
( )
- + ´ ³
V R R I 20
C ext S C
ANSIEQUATION16063 V1 EN
V Operating voltage over the supervised trip circuit
c
I Measuring current through the trip circuit, appr. 1.0 mA (0.85...1.20 mA)
c
R external shunt resistance
ext
R trip coil resistance
s
If the external shunt resistance is used, it has to be calculated not to interfere with the
functionality of the supervision or the trip coil. Too high a resistance causes too high a
voltage drop, jeopardizing the requirement of at least 20 V over the internal circuit, while
a resistance too low can enable false operations of the trip coil.
Table 16: Values recommended for the external resistor R
Operating voltage U
c
48 V DC
60 V DC
110 V DC
220 V DC
Due to the requirement that the voltage over the TCSSCBR contact must be 20V or higher,
the correct operation is not guaranteed with auxiliary operating voltages lower than 48V
DC because of the voltage drop in the R
feeding auxiliary voltage system which can cause too low voltage values over the
TCSSCBR contact. In this case, erroneous alarming can occur.
Secondary system supervision
V DC
Shunt resistor R
10 kΩ, 5 W
22 kΩ, 5 W
33 kΩ, 5 W
68 kΩ, 5 W
and operating coil or even voltage drop of the
ext
Section 10
(Equation 175)
ext
ext
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