ABB Relion 650 Series Applications Manual page 118

Section 9
Secondary system supervision
Several trip-circuit monitoring functions parallel in circuit
Not only the trip circuit often have parallel trip contacts, it is also possible that the circuit has
multiple TCSSCBR circuits in parallel. Each TCSSCBR circuit causes its own supervising current to
flow through the monitored coil and the actual coil current is a sum of all TCSSCBR currents. This
must be taken into consideration when determining the resistance of R
Trip-circuit monitoring with auxiliary relays
Many retrofit projects are carried out partially, that is, the old electromechanical relays are
replaced with new ones but the circuit breaker is not replaced. This creates a problem that the coil
current of an old type circuit breaker can be too high for the protection IED trip contact to break.
The circuit breaker coil current is normally cut by an internal contact of the circuit breaker. In case
of a circuit breaker failure, there is a risk that the protection IED trip contact is destroyed since the
contact is obliged to disconnect high level of electromagnetic energy accumulated in the trip coil.
An auxiliary relay can be used between the protection IED trip contact and the circuit breaker coil.
This way the breaking capacity question is solved, but the TCSSCBR circuit 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:
(
-
V R
C ext
ANSIEQUATION16063 V1 EN-US
V
c
I
c
R
ext
R
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.
112
Setting the TCSSCBR function in a protection IED not-in-use does not typically
affect the supervising current injection.
)
+ ´ ³
R I 20 V DC
S C
Operating voltage over the supervised trip circuit
Measuring current through the trip circuit, appr. 1.0 mA (0.85...1.20 mA)
external shunt resistance
trip coil resistance
© Copyright 2013 ABB. All rights reserved
1MRK 505 287-UUS B
.
ext
(Equation 29)
Busbar protection REB650
Application manual