S150-34-1
15
4 FEEDER INPUT MODULE M-BF3
M-BF3 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-BF3 or M-BC3.
With reference to the block diagram SCE1577 the module M-BF3 receives the
measuring input from the three Feeder’s Current transformers (eventually from
the ratio adapting transformers) and the configuration input from the position
signal contacts of the busbar selection isolators.
For each isolator 1 N/O and 1 N/C contacts are needed for controlling the isolator
repeat bistable relays A and B which perform the replica of the busbar system’s
configuration.
For each phase the input current is fed to a pair of internal current transformers:
q One current transformer is changed over by the repeat relays to the wiring
bus connected to the Differential relay relevant to the Zone (1 or 2) where the
feeder is actually switched on.
Each of the two zone wiring bus also includes the wire carrying the trip signal
of its Differential Relay: the trip coil of the feeder’s Circuit Breaker is switched
over to the proper wiring bus by one contact of the repeat relays.
The second current transformer feeds the bus wiring of the check zone and
the saturation detection circuit; this circuit is used to inhibit the tripping of the
differential element due to CT’s saturation during external faults.
q Power Supply is fed to all the M-BF3 modules from the Power supply unit
included in the F/C rack panel.
The operation of the repeat relays is monitored by a Discrepancy Alarm feature which by means of an XOR
(Exclusive OR) logic operates an output relay if both set and reset signals are simultaneously present or no
signal is present at the terminals of repeat relay A or B (the relay is normally energized with a N/C contact).
The Discrepancy Alarm Relay’s pick-up is time delayed by approximately 8 sec. and it is signaled by an LED
on the relay’s front panel.
One push button on the relay’s front panel permits testing of the Discrepancy Alarm function: the push button
must be pressed for approximately 8 sec. to get the Alarm pick-up.
The position of each isolator is monitored by a pair of LEDs on relay’s front face.
Wiring is made according to the diagram SCE1577 :
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-BF3’s card.
q Through the same terminal 5 which sends the trip signal to the Feeder’s Circuit Breaker, a trip signal
coming from the Feeder’s Breaker Failure Relay can be sent back to the tip Bus of the zone to which the
Feeder is connected

51mm

FEEDER INPUT MODULE
M-BF3
DISCREPANCY
ALARM
TEST
OC
OC