ABB Relion SMU615 Technical Manual page 137

1MRS758407 B
SMU615
Technical Manual
A070972 V4 EN
Figure 90: Incorrect connection of trip-circuit supervision
A connection of three merging units with a double pole trip circuit is shown in the
following figure. Only the merging unit R3 has an internal TCS circuit. In order to test
the operation of the merging unit R2, but not to trip the circuit breaker, the upper trip
contact of the merging unit R2 is disconnected, as shown in the figure, while the lower
contact is still connected. When the merging unit R2 operates, the coil current starts
to flow through the internal resistor of the merging unit R3 and the resistor burns
immediately. As proven with the previous examples, both trip contacts must operate
together. Attention should also be paid for correct usage of the trip-circuit supervision
while, for example, testing the merging unit.
Section 5
Supervision functions
131