Manual Part 5

BFU-21
1 Product Overview
The BFU-21 supplies b attery backup system voltage to the RBS and
disconnects the battery when it has reached its lower discharge limit. The
contactor can disconnect and reconnect the battery with a control signal from
the Supervision Module (SM).
1.1 Main Functions
The BFU-21 has the following functions:
• Supplies priority power to transmission equipmen t. Power to transmis sion
equipment can be distributed ev en if a batte ry is not present. The rela y can
select the pow er source with a control signal from the SM
• Supplies priority power to the EC output. The EC output is protected from
reverse currents by a diode. Power to the EC output can be distributed
even if a battery is not present. The re lay can select the power source
with a control signal from the SM
• Communicates on the Environmental and Power Control (EPC) bus (opto
cable) with the Distribution Switch Unit (DXU). If the EPC bus is no t present,
the BFU -21 operates at its default values. The battery voltage, current and
temperature are monitored and alarms are sent on the EPC bus
• Disconnects the batteries, if the voltage i s too low or the temperature is too
high. Reconnects the batteries when t he temperature returns to normal
• Sends a ‘‘Battery temperature sensor fault’’ message to the DXU w hen the
battery temperature is faulty
• Disconnects battery backup manually o r by control signals on the EPC bus
The SM provides self-detection of inte rnal faults and stores them in non-volatile
memory.
2 Dimensions
The phy sical characteristics of the B FU-21 are shown in the table below.
Table 1 BFU-21 Size a nd Weight
Height Width Depth Weight
267 mm 82 mm 226 mm 5 kg
3 (8)
EN/LZT 720 0234 Uen R2A