DC SVCE/UTLY BUS Pushbutton controls connection/disconnection of DC SVCE BUS and both UTLY BUSSES to associated main DC BUSSES. The 'SHED' amber indication comes on and the FWS is activated when a load shed condition controlled by the BPCU is present and:
The source of constant frequency (400 Hz) AC power consists of two static inverters (INV). The two inverters are powered respectively from DC BUS 1 and DC BUS 2. The input voltage range is between:
The ACW generation system consists of two 'propeller' driven three phases generators. Each generator is a brushless, air cooled type and is rated to deliver 60 KVA for continuous operation.
It is rated to deliver 20 KVA for continuous operation. Nominal set voltage is 115 V / 200 V. Normal operating frequency range is 341 to 488 Hz (70 to 100 % NP).
TRU Pushbutton – When the Pb is pressed in (ON). The TRU is connected to ACW BUS 1.
The TRU is connected to ACW BUS 2.
In starter mode, the starter/generator is connected to:
The INV FAULT Light will come on in case of:
The GND HDLG BUS supplies the DC loads required for aircraft servicing on the ground even with BAT sw selected OFF.
Since these loads are not required during flight, the GND HDLG BUS is deenergized in flight.
The electrical power generation is provided by the following sources:
Assuming normal operation in flight, how is the constant AC PWR frequency obtained?
A Generator Control Unit (GCU) associated with each generator provides the control for the generator contactor and the start contactor.
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Starter/generator switches to starter mode when the crew initiates associated engine starting sequence by pressing the START pb (on the ENG START panel). The START ON light turns on. During the start sequence, the starter/generator rotates the rotor up to self-sustaining speed. The start sequence automatically ends when NH reaches _____ and associated engine START ON light turns off.
Due to system components tolerance, the start sequence may end with displayed NH between 42% and 48%
____ is installed in order to maintain the batteries when DC power is under emergency supply conditions (both generators failed).
In this configuration, emergency DC system can be supplied by the ACW (Alternating Current Wild Frequency) electrical system, through the TRU.
In event of both DC BUS power loss, INV 1 is automatically supplied by:
INV 1 normally supplies:
As soon as EXT PWR is connected, selected ON and checked 'acceptable' in voltage, frequency, phase, and current by the BPCU, it has priority over the engine driven generators.
If OAT exceeds ISA+25 during single DC GEN operation in flight, flight level must be limited to:
When the engine reaches _____, the starter/generator is acting as a generator.
Provided associated DC GEN pb is selected and EXT PWR is not used, each generator feeds associated DC BUS through a Generator Contactor (GC).
Two separate networks (left and right) run individually and can be connected in case of generation failure thanks to Bus Tie Contactors (BTC).
Three sources can be used for the 28 VDC emergency supply:
The BAT three positions toggle switch is used to provide DC electrical power from the EMER battery to the EMER BUS, the main battery to the ESS BUS, and DC STBY BUS, and through the INV 1, to the AC STBY BUS. The OVRD position:
This position is protected by a toggle guard.
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A 24V Ni-Cd battery (main BAT) is provided for engine starting and for emergency power supply including propeller feathering.
The Bus Tie Contactor (BTC) enables DC BUS 1 and 2 to be on line when:
There are two static inverters that provide DC power from the Main AC Busses.
Two static inverters (supplied by the DC system) provide constant frequency AC power.
Inverter 1 normally supplies:
The DC BUS 1 is normally supplied by the LH engine driven generator and the main battery. The DC BUS 2 is normally by the RH engine driven generator or the main battery.
The DC BUS 1 is normally supplied by the LH engine driven generator and the DC BUS 2 by the RH engine driven generator.
EMER BAT CHG and MAIN BAT CHG Pushbuttons control the operation of the associated Battery Charge Contactor (BCC). The 'FAULT' light comes on amber and the MFC is activated in event of:
An overheat detected by the MFC. In this case, the charge contactor automatically opens or a failure of the charge contactor.