M-LIB3 Low Impedance Bus Differential Relay
18
5 BUS COUPLER INPUT MODULE M-BC3
M-BC3 is a 51mm wide draw-out modular unit to be plug-in into the F/C rack
panel that can house up to 7 modules M-BC3 or M-BF3.
With reference to the block diagram SCE1578 the module M-BC3 receives the
measuring input from the two sets of the Bus Coupler’s current transformer
(eventually from the ratio adapting transformers).
Two sets of internal current transformers convey the current inputs from the bus
1 and the current inputs from the bus 2 respectively to the wiring bus connected
to the Differential Relay of the Zone 2 and to the wiring bus connected to the
Differential Relay of Zone 1.
q Each of the two zone wiring bus also includes the wire carrying the
trip signal of its Differential Relay :
the trip coil of the Bus Coupler’s Circuit Breaker is energized by both the zone
trip signals. It means that any fault on the bus bar system always trips the bus
coupler.
q Power Supply is fed to all the M-BC3 modules from the Power supply unit
included in the F/C rack panel :
each module includes its independent power supply unit.
q Via Terminal 6 the trip signal to Bus Coupler Circuit Breaker can also be
received from the Field (for example from any or all the Feeders’ Breaker
Failure relays)
q Via Terminal 7 a trip signal can be conveyed from the field to both the tripping
Bus of Zone 1 and Zone 2 (for example from the Breaker Failure Relay of the
Bus Coupler)
Wiring is made according to the diagram SCE1578 :
q Field wires are connected to the module’s terminal board available on the back of the F/C rack panel.
q Connections to the zone bus wiring are made by the plug-in connector of the M-BC3’s card.
51mm
BUS COUPLER INPUT
MODULE M-BC3