ABB RELION REX640, Техническое руководство, Страница: 1308 / 1960

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 U I R R V AC DC
C D C s ext
− − ⋅ + ≥
( ) / 20
(Equation 314)
U
c
Operating voltage over the supervised trip circuit
U
D
Voltage drop over internal 3 mA current drain, about 6.5 V
I
c
Measuring current through the trip circuit, appr. 1.5 mA (0.99...1.72 mA)
R
ext
External shunt resistance
R
s
Trip coil resistance
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 1238: Values recommended for the external resistor R ext
Operating voltage U
c
Shunt resistor R
ext
48 V AC/DC 1.2 kΩ, 5 W
60 V AC/DC 5.6 kΩ, 5 W
110...130 V AC/DC 22 kΩ, 5 W
220...250 V AC/DC 33 kΩ, 5 W
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 U
D
and R
ext
and the operating coil
or 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 recommend either
touse the static output and single-pole connection (as then there is no internal
currentdrain and U
D
= 0 V), or not to use R
ext
and block TCS when the circuit breaker
isopen.
Supervision functions 1MRS759142 F
1308 REX640
Technical Manual