ABB RELION SMU615 Technical Manual page 140

Supervision functions
An auxiliary relay can be used between the merging unit trip contact and the circuit
breaker coil. This way the breaking capacity question is solved, but the TCS circuit in
the merging unit 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
C
U
c
I
c
R
ext
R
int
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.
Table 169: Values recommended for the external resistor R ext
Operating voltage U
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
even voltage drop of the feeding auxiliary voltage system which can cause too low
voltage values over the TCS contact. In this case, erroneous alarming can occur.
At lower (<48 V DC) auxiliary circuit operating voltages, it is recommended to use
the circuit breaker position to block unintentional operation of TCS. The use of the
position indication is described earlier in this chapter.
140
(R R R ) I
− + + × ≥
ext int s c
Operating voltage over the supervised trip circuit
Measuring current through the trip circuit, appr. 1.5 mA (0.99...1.72
mA)
external shunt resistance
internal shunt resistance, 1 kΩ
trip coil resistance
c
20 V AC DC /
Shunt resistor R
1.2 kΩ, 5 W
5.6 kΩ, 5 W
22 kΩ, 5 W
33 kΩ, 5 W
1MRS758407 C
(Equation 4)
ext
,R and the operating coil or
int ext
Technical Manual
SMU615