Electrics Flashcards
Where are the external power receptacles located?
Right side of the fuselage on the FOs side of the nose gear
What does the TRU do?
Converts 115 VAC into DC power
How are the left and right networks connected?
Through bus tie contractors in the event of a failure
Where is the Bus Power Control Unit located
Avionics rack behind the FOs seat
Two independent BPCUs control the AC and DC systems, one for each
What powers the 28VDC system?
Two engine driven starter/generators or an external ground power unit
Two batteries provide a source of power for emergencies or for when the aircraft is on the ground without engines running and no external GPU
What Powers the DC bus 1 and DC bus 2?
They are powered by their respective generators
What powers rhe DC emer bus and DC stby bus?
Powered by DC Bus 1 through the hot emergency battery bus
How will the DC emergency and standby bus be powered if neither DC bus is operating?
The TRU (converts ACW power into DC power)
If the TRU is not operating they will be powered by the hot emergency battery bus
What powers the DC ESS bus?
DC Bus 2 through the hot main battery bus
What are the two utility buses used for
They power non essential loads
They are powered by their respective DC bus through a utility Bus Contacter
Automatically she in the event of an overload of the DC buses
What are the battery ratings?
Main Battery - 24V Nicad battery rated at 43 AH
Emergency Battery - 24V Nicad battery rated at 15 AH
What is the main battery normally used for?
Engine starting
Also a source of emergency power
What is the function of the emergency battery?
- ensures that the emergency electrical network is powered even if the main battery is depleted
- prevent power transients on critical equipment during engine starts
What monitors the charge of the batteries?
The MFC - they will automatically connect the battery to the associated DC bus to allow it to charge
They will monitor the bus voltage to prevent a thermal runaway condition or an abnormal battery operating condition
What usually supplies the hot battery buses?
Hot emer bat bus - DC Bus 1
Hot main bat bus - DC bus 2
Where can the voltage and current of each battery be checked?
On the lateral maintenance panel by placing the selector knob to the BAT MAIN or EMER position
What happens when external power is connected?
The External Ground Handling Relay closes and the Battery Transfer Relay opens
Ground power then supplies power to the ground handling bus through the DC SVCE bus provided the flight attendant GND SVCE BUS pb is on
Powering of ground handling bus does not require external power to be selected on
What does the Ground Handling Bus provide power to?
- Cargo doors control and indicators
- fueling control and indicators
- entrance light
Ground handling bus is de-energised in flight
What does the DC Service Bus supply power to?
Power to the galleys, lights, lavatory system and the auto feather pump manual control
What powers the DC service bus
Either DC Bus 1 or external power
What does the DC SVCE/UTLY BUS switch do?
Button gives the flight crew master control of the GND SVCE BUS DC pb on flight attendants panel
How is the DC system powered when the engines aren’t running?
By the battery system
What supplies DC power when the engines are running?
Two DC starter generators
Function as a starter during engine start and a DC generator when the engines are running
What drives the DC starter generator?
The associated engine accessory gear box
What power do the generators produce?
Between 27 and 31 V, with a nominal setting of 30 V
Output of 12 KW of power
How are the generators cooled?
Air
If only battery power is available, what powers the starter generator?
Powered by the main battery through the battery start contacter
What powers the starter generator if external power is available?
Powered by the DC external power through the external power contactor
What is a cross start?
Once an engine is running, the second engine is connected to the main battery and the operating generator (on the ground)
During a cross start, when will the generator on the running engine connect to the start bus?
NH 10% until NH reaches 45%
What indications will you get if a cross start fails?
- amber CROSS START FAIL light on DC power control panel
- single chime
- ELEC will illuminate on the CAP
- ELEC light will go out at 45% NH
When does the starter generator stop cranking the engine?
At 45%NH the start contacter opens
When will the starter generator act as a generator
61.5% NH
What does the GCU (Generator Control Unit) provide fault protection and detection for?
- over/under voltage
- over/under speed
- differential fault current
- generator overload
- power and fault current limiting
- bus tie lockout
- reverse current
- equalising load
What has priority?
External power has priority over the engine generators as
How are the DC buses powered if only one engine operating
The operating generator can power both DC buses through the Bus Tie Contactor
Position of the contractor is indicated by the green flow bar
What does the AC network consist of?
A 115 VAC network and a 26 VAC network
Power is supplied by two inverters
The inverters require DC power in the range of 18-31
Each inverter produces 115 VAC and 26 VAC at frequency of 400 Hz
What does the 115 VAC network consist of?
AC Bus 1
AC Bus 2
AC stby bus
During normal ops, what do the inverters power?
Inverter 1 - AC bus 1 and the AC stby bus
Inverter 2 - AC bus 2
How are the two 115 VAC buses connected?
Through an AC bus tie relay which will close automatically in the event one of the inverters fails or is not powered
If inverter 1 fails, how is the AC stby bus powered?
By inverter 2
What does the 26 VAC system consist of?
AC Bus 1
AC Bus 2
AC stby bus
What powers the AC Wild system
Two propeller driven AC generators
Air cooled
Deliver 20 KVA
Produce between 115 and 200 V at a frequency range between 341 and 488 Hz - freq depends on prop speed
What does the AC Wild service bus power?
High draw items such as the galley and AC Wild service plugs
Powered by AC Wild bus 1 when engines are running or AC External power
If the aircraft is unpowered, how is the AC Wild service bus powered?
By pressing the AC SERVICE BUS push button on the flight attendant panel
What happens if both DC generators failed?
The TRU will convert AC Wild power into DC power which powers the DC system
When will a FAULT light illuminate on the DC GEN pb?
If the GCU trips the generator due to a fault or if the associated generator contractor opens
The bus tie contacter will close
When will the generator reset itself after a FAULT?
If the GCU detected an under speed of the generator, it will reset itself automatically once the generator returns to normal speed
When will th SHED caption illuminate?
When the BPCU senses an overload condition on one of the main DC buses and at least one utility bus is disconnected from the associated main DC bus
Single chime, master caution, and ELEC amber light
When will the MFC open the battery charge contacter?
- if it detects thermal runaway of the battery
- if the associated DC MAIN bus voltage is less than 25 V
- if main battery switch is in the override position
- both contacters will be opened during engine start - they will close when the start selector is out of the start position
What do two amber flow arrows mean?
Either one of the batteries are being discharged
Right arrow - DC essential bus is powered by the main battery
Left arrow - emergency battery is supplying the DC emergency bus
What do two amber flow arrows mean?
Either one of the batteries are being discharged
Right arrow - DC essential bus is powered by the main battery
Left arrow - emergency battery is supplying the DC emergency bus
What does the UNDV caption mean?
DC Standby bus voltage is less than 19.5 V
When will the inverter fault light illuminate?
In the event of an under voltage or over voltage
Also single chime, master caution light, ELEC light on CAP
When will an AC Wild generator reset itself automatically?
If the fault was due to an NP over speed that lasted less than three seconds, or if it was due to a generator under speed
