ABB RELION 620 Series Technical Manual page 590

Section 6
Supervision functions
584
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 TCM 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:
− (R + + ) ×
V R R I
C ext int s c
A070986-ANSI V1 EN
V 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 423: 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 TCM contact must be 20 V or higher, the
correct operation is not guaranteed with auxiliary operating voltages lower than 48 V DC
≥ 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
1MAC504801-IB E
(Equation 89)
ext
ext
620 series ANSI
Technical Manual