ABB RELION 620 Series Technical Manual page 591

1MAC504801-IB E
620 series ANSI
Technical Manual
because of the voltage drop in the R
feeding auxiliary voltage system which can cause too low voltage values over the TCM
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 TCM. The use of the position
indication is described earlier in this chapter.
Using power output contacts without trip circuit supervision
GUID-548E2DC1-D16E-4BC2-803F-96FB5021DAC2-ANSI V1 EN
Figure 295: Connection of a power output in a case when TCM is not used and the
internal resistor is disconnected
Incorrect connections and use of trip circuit supervision
Although the TCM circuit consists of two separate contacts, it must be noted that those are
designed to be used as series connected to guarantee the breaking capacity given in the
technical manual of the protection relay. In addition to the weak breaking capacity, the
internal resistor is not dimensioned to withstand current without a TCM circuit. As a
result, this kind of incorrect connection causes immediate burning of the internal resistor
when the circuit breaker is in the close position and the voltage is applied to the trip circuit.
The following figure shows incorrect usage of a TCM circuit when only one of the
contacts is used.
Supervision functions
and operating coil or even voltage drop of the
ext
Section 6
585