ABB RELION Series Technical Manual page 521

1MRS758755 A
REC615 and RER615
Technical Manual
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 relay 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 relay trip contact and the circuit
breaker coil. This way the breaking capacity question is solved, but the TCS circuit in
the protection relay monitors the healthy auxiliary relay coil, not the circuit breaker
coil. The separate trip circuit supervision 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 20 V
(15...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, a fault is detected.
Mathematically, the operation condition can be expressed as:
U (R R R ) I
− + + ×
C ext int s
A070986 V2 EN
U Operating voltage over the supervised trip circuit
c
I Measuring current through the trip circuit, appr. 1.5 mA (0.99...1.72 mA)
c
R external shunt resistance
ext
R internal shunt resistance, 1 kΩ
int
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 529: Values recommended for the external resistor R
Operating voltage U
c
48 V AC/DC
60 V AC/DC
110 V AC/DC
220 V AC/DC
Due to the requirement that the voltage over the TCS contact must be 20 V or higher,
the correct operation is not guaranteed with auxiliary operating voltages lower than 48
V DC because of the voltage drop in R
20 V AC DC /
≥
c
Shunt resistor R
1.2 kΩ, 5 W
5.6 kΩ, 5 W
22 kΩ, 5 W
33 kΩ, 5 W
,R and the operating coil or even voltage
int ext
Section 6
Supervision functions
(Equation 65)
ext
ext
515