Electrical system Flashcards
What is the purpose of the Electrical Power Generation and Distribution System (EPGDS)?
It supplies electrical energy for all onboard electrical equipment and provides energy conversion
What are the components of the DC generation system in the Q400?
The DC generation system includes three NiCad batteries
How is power distributed in the Q400 electrical system?
Power is distributed by an electrical bus system that reconfigures automatically during individual power source and bus failures by opening and closing bus tie contactors.
How can AC and DC aeroplane services be operated?
They can be operated from the AC generators or AC external power alone.
What is the function of the ELEC SYS pushbutton on the ESCP panel?
It displays the electrical system page on the MFD when set to SYS. There is no action with another push.
What happens when the STBY BATT switch is selected ON?
It connects the standby battery to the left main feeder bus unless external power is connected
What does the AUX BATT switch control?
It connects the auxiliary battery to the left main feeder bus
What does the MAIN BATT switch do?
It connects the main battery to the right main feeder bus under normal operations and disconnects during emergency conditions or when a bus fault is present.
What is the purpose of the BATTERY MASTER switch?
It disconnects or connects the main
What is the function of the GEN 1 and 2 switches?
They allow the DC GCU to connect the generators to their associated feeder buses.
How does the MAIN BUS TIE switch operate?
It manually ties the left and right main feeder buses
What happens when the BUS FAULT RESET switch is pressed?
It reinitializes the EPCU after a bus isolation to enable subsequent bus fault monitoring.
What is the role of the DC EXT PWR switch?
It powers the left and right main feeder buses
What voltage tolerance must be met for the DC EXT PWR to be connected?
The applied voltage must be within 22 ± 1VDC to 31 + 0.5/-0.75VDC.
What is the function of the AC EXT PWR switch?
It connects AC external power to the variable frequency buses and powers all AC and DC buses on the aeroplane.
What is the purpose of the External Power Protection Unit (AC PPU)?
It ensures only AC power within specifications is allowed on the bus.
How is the AC PPU activated?
By checking for voltage level
What system monitors electrical parameters in the flight deck?
The Electronic System Indicating Displays (ESID) monitor system parameters.
What are the main sources of DC power on the Q400?
Main
What is the priority of DC buses in the Q400?
The priority is Battery
Where are the main and auxiliary batteries located?
In the lower left nose compartment of the aircraft.
What capacity do the main and auxiliary batteries have?
They each have a capacity of 40 amp-hours.
How long can the aircraft operate on batteries in flight?
The aircraft can operate for 45 minutes or more using battery power for essential services.
What happens when the BATTERY MASTER switch is turned ON?
Three contactors close
Can battery power be applied to the secondary buses?
No
What temperature limitation applies to battery operation?
Battery temperature should be equal to or greater than -20°C prior to dispatch
What are the charging characteristics of the 40Ahr batteries?
Charging voltage must be between 28 and 32 VDC for full recharging. A low voltage cart cannot fully charge the batteries.
What happens if DC external power voltage is below 28VDC?
The batteries will discharge and not be fully restored.
What is the function of the starter/generators?
They act as starter motors and revert to generator operation after engine start to supply 28.5VDC to the feeder buses.
What is the role of the Generator Control Unit (GCU)?
It monitors and controls generator output and disconnection in case of faults.
What are Transformer Rectifier Units (TRUs) responsible for?
They convert 115-volt variable frequency AC power into 28VDC for the aircraft’s DC buses.
Where are the TRUs located?
In the nose of the aircraft.
What happens if a TRU fails?
The EPCU reconfigures the power system
How does the APU Starter/Generator function?
It supplies 28VDC to the essential
How is fault tolerance achieved in the DC power system?
The EPCU automatically reconfigures power flow and ensures operation with up to two power source failures.
What happens when both DC generators fail in flight?
The TRUs supply DC power to both the main and secondary buses through vertical bus ties.
What occurs during emergency mode in the EPCU?
The batteries disconnect from the main buses
What protection is provided for the DC buses?
The EPCU and DC GCUs protect against short circuits on the main and secondary buses.
What happens when a main bus fault occurs?
The EPCU isolates the bus
What caution lights come on during a main bus fault?
The MAIN BATTERY or AUX and STBY BATTERY caution lights
What is the function of the MAIN BUS TIE switch during a fault?
It is locked out by the EPCU and cannot be operated manually.
How does the EPCU react if a secondary bus fault occurs?
It transfers the fault to the opposite TRU
How are engine starts powered in the Q400?
Engine starts can be powered by batteries
What batteries are used for starting if ground power is unavailable?
The main and auxiliary batteries are used for engine starting.
How does the EPCU monitor bus faults during engine starting?
The EPCU disconnects the standby battery during the start sequence and reconnects it afterward.
What is the role of the vertical and horizontal bus ties?
They connect main and secondary buses during power source failures or faults.
What is the maximum current provided by the starter/generators?
The starter/generators provide a maximum of 400 amps.
What type of overheat protection is provided for the TRUs?
The TRUs have overheat sensors that activate caution lights when the temperature exceeds the limit.
What happens if a TRU overheats?
The corresponding TRU HOT caution light comes on
What is the purpose of the AC GEN caution lights?
They indicate that the AC generators are not supplying power to the variable frequency buses.
What type of batteries are used in the Q400?
NiCad batteries
How many main batteries does the Q400 have?
Two
Where are the main batteries located?
Lower left nose compartment
What voltage do the TRUs convert AC to?
28 VDC
How many engine-driven starter/generators are there?
Two
What does the EPCU stand for?
Electrical Power Control Unit
What is the nominal voltage of a fully charged battery?
24 VDC
Where is the standby battery located if no APU is installed?
Tail compartment
What is the capacity of the auxiliary battery?
40 amp-hours
What is the voltage of AC generators in the Q400?
115 Volts AC
What color is the DC EXT PWR ON indication on the MFD?
Green
What happens when the MAIN BUS TIE switch is set to ON?
It connects the left and right main feeder buses
What is the purpose of the BUS FAULT RESET switch?
To reinitialize the EPCU
What does the DC EXT PWR switch do?
Powers the buses from DC external power
What is the maximum DC voltage tolerance for the external power connection?
31 VDC
How many Transformer Rectifier Units (TRUs) are in the Q400?
Two
At what engine speed does the starter/generator switch to generator mode?
50% NH
What is the maximum output of the starter/generator in amps?
400 Amps
What is the voltage range of the TRUs during operation?
26 to 29 VDC
Where is the APU starter/generator located?
Tail cone section
What does the L TRU caution light indicate?
The left TRU is offline or failed
How long can the aircraft operate on batteries during emergency flight?
45 minutes or more
What is the nominal output of the APU starter/generator?
28 VDC
How does the EPCU handle a bus fault?
It isolates the bus and locks out the contactors
How many bus tie contactors are there in the Q400 DC system?
Four
What condition triggers the EPCU to operate in emergency mode?
Loss of both DC generators and at least one TRU
What does the EPCU monitor for the DC subsystem?
Bus faults and short circuits
What does the DC GEN caution light signify?
The generator is not supplying power to the bus
What happens when both TRUs fail?
DC generators power both main and secondary buses
What causes the MAIN BAT HOT warning light to come on?
High battery temperature
What voltage must be met for batteries to recharge fully from an external DC cart?
At least 28 VDC
What are the two conditions under which the standby battery is automatically disconnected?
DC external power connected
What is the maximum temperature that causes the battery temperature digits to turn yellow?
50°C to 65°C
What is the main function of the Generator Control Unit (GCU)?
To control and monitor the generator’s output
What happens if the EPCU detects a fault on the main bus?
The EPCU isolates the bus and sends a trip signal to the GCU
What does the EPCU do when it operates in emergency mode?
Disconnects the batteries from the main buses
Where are the TRUs located on the Q400?
In the nose section
What protection is built into the external DC power supply system?
External DC Power Protection to avoid incorrect voltage or polarity
What is the voltage trip point for the AC external power under-voltage protection?
106 VAC
What happens if the AC PPU detects incorrect phase rotation?
AC external power is not allowed on the bus
What is the function of the MAIN BUS TIE switch during a fault condition?
It is locked out by the EPCU
How does the EPCU handle an overheat condition on the generator?
The #1 DC GEN HOT or #2 DC GEN HOT light comes on
What condition will cause the standby battery to be diode isolated during engine start?
Battery power alone is used during engine start
How many essential buses are powered by the battery master switch?
Two
What type of electrical power does the APU generator provide?
28VDC
What happens if a TRU overheat condition persists?
The TRU will be taken offline
Which buses are automatically reconfigured by the EPCU during power source failure?
Main and secondary buses
What is the maximum over-voltage trip point for AC external power?
124 VAC
What is the output power capacity of the TRUs in amps?
300 Amps max
What indication is shown when DC external power is connected correctly to the aircraft?
DC EXT PWR ON indication (green) on the MFD
What is the purpose of the EPGDS in the Q400?
To supply electrical energy for onboard electrical equipment
How many TRUs are in the Q400 electrical system?
Two
How does the DC generation system reconfigure in case of power source failure?
By automatic closing and opening of bus tie contactors
What is the voltage output of the Q400’s AC generators?
115 VAC
What powers the 28VDC system in the Q400?
Two Transformer Rectifier Units (TRUs)
How is external power connected to the aircraft’s electrical system?
Through external AC or DC power receptacles
What is the function of the ESCP pushbutton for electrical system display?
It displays the electrical system page on the MFD
What does the STBY BATT switch do?
It connects the standby battery to the left main feeder bus
How many batteries can power both essential buses when selected?
Any battery can power both essential buses
What happens when the GEN 1 or GEN 2 switch is turned off?
The associated generator shuts off
What does the BUS FAULT RESET switch do?
It reinitializes the EPCU after a bus fault
What happens when the external DC power is connected correctly?
The DC EXT PWR ON indication shows green
How does the EPCU protect against incorrect DC external power?
It monitors voltage
What is the function of the external power switch for AC power?
It connects AC external power to the variable frequency buses
What protection is provided for AC external power?
External Power Protection Unit (AC PPU)
What color indicates that AC external power is connected?
Green
How are electrical parameters monitored in the flight deck?
Through the Electronic System Indicating Displays (ESID)
What type of batteries are located in the Q400 nose compartment?
Main and auxiliary batteries
How many amps are the main and auxiliary batteries?
40 amp-hours each
What happens when the BATTERY MASTER switch is turned on?
It connects all three batteries to the essential buses
Can battery power be applied to the secondary buses?
No
What battery temperature should be met before dispatch?
Equal to or greater than -20°C
How much load is supplied by the starter/generator after engine start?
28.5 VDC and up to 400 Amps
What happens if a generator overheat condition occurs?
The DC GEN HOT caution light comes on
What do TRUs convert AC power to?
28 VDC
How are the TRUs cooled?
By internal cooling fans
What happens when a TRU fails?
The EPCU reconfigures the system and the other TRU powers both secondary buses
Where is the APU starter/generator located?
In the tail cone section
What is the main function of the APU starter/generator?
To supply 28VDC to the DC buses on the ground
What happens when both DC generators fail?
The TRUs power both main and secondary buses
How does the EPCU ensure mission completion after power source failure?
By automatically reconfiguring the bus system
What is the function of the vertical bus tie contactors?
They connect main and secondary buses in case of power source failure
What happens during emergency mode in the EPCU?
The batteries disconnect from the main buses
What triggers the EPCU to operate in emergency mode?
Loss of both DC generators and at least one TRU
What happens during a main bus fault?
The EPCU isolates the bus and locks out the contactors
What does the MAIN BAT HOT warning light indicate?
High main battery temperature
How are main bus failures handled?
The EPCU isolates the affected bus and trips the GCU
What happens when a secondary bus fault occurs?
The fault is transferred to the opposite TRU
How are the starter/generators connected to the bus system?
Through the Generator Control Unit (GCU)
What is the output of the TRU in amps?
300 Amps max
How are batteries charged during flight?
By the DC generators supplying 28.5 VDC
What happens if external power cart voltage is below 28 VDC?
The batteries will discharge
What is the output voltage range of the TRUs?
26 to 29 VDC
What happens if both TRUs and generators fail?
The EPCU isolates the buses and connects the batteries for emergency power
