12.5.6.7 Main Bus Failures
If a main bus fault occurs, the EPCU prevents the upper horizontal and two vertical bus ties from
closing, isolating the bus. The DC BUS caution light comes on to warn of the fault impending
condition.
If the fault persists after approximately 5 seconds, the EPCU sends a TRIP signal to the GCU,
isolating the affected generator. The EPCU will also open and lock-out the contactors connecting
the batteries to the affected main bus. The MAIN BATTERY or AUX and STBY BATTERY caution
light(s) and related DC GEN caution light will come on as a result. The EPCU continues to moni-
tor the operating buses. All main DC services on the faulted bus side will not function.
NOTE:
Manual operation of the main bus tie through the MAIN BUS TIE switch is not possi-
ble once the EPCU has reacted to a fault.
If the fault subsequently clears, power may be restored with the BUS FAULT RESET switch.
12.5.6.8 Secondary Bus Failures
In the case of a secondary bus short, the over current condition will immediately trip the associ-
ated TRU primary circuit breaker. Seven seconds later, with the EPCU declaring TRU failed the
contactor L to R Secondary bus tie will close, transferring the short circuit to the opposite side
TRU. At that moment, the cross tie fuse is blown isolating the fault. This is indicated by a L TRU
or R TRU caution light and loss of services on the associated secondary bus.
Dash8 - Q400 - Electrical
To Next Page
Loading...