Electrical Flashcards
What components make up the AC Electrical System?
2 engine driven 115vAC Generators
What components make up the DC Electrical System?
3 24vDC, 40 amp NiCad batteries
2 28vDC, 400 amp Engine Driven Starter Generators
2 28vDC, 300 amp Transformer-Rectifiers
1 28vDC, 400 amp APU DC Generator
7 DC Busses: Hot Battery Bus Left and Right Main Busses Left and Right Secondary Busses Left and Right Essential Busses
Where are the Main, Aux and Standby Batteries are located?
Main: Lower left side of the nose, forward
Auxiliary: Lower left side of the nose, aft
Standby: Upper left side of the nose
Which batteries assist with engine starts?
Only the Main and Aux batteries
In an emergency, all 3 batteries power the Essential DC Busses providing emergency power for approximately _______?
45 minutes
What does the Standby battery do?
Powers the Hot Battery Bus
What is the max battery load meter reading for starting an engine?
Below 0.4 on the MFD Electrical Page
What does the Battery Master Switch do?
Directly connects all 3 batteries to the Essential DC busses. Independent of the EPCU
Powered by a direct lead from the Standby Battery
What does the Main Battery Switch do?
Directly connects the Main Battery to the Right Main Bus for two-way power flow.
What does the AUX Battery Switch do?
Connects the Aux Battery to the Left Main Bus for two-way power flow.
What does the STBY Battery Switch do?
Connects the Standby Battery to the Left Main Bus for charging only
What are the temperatures and colors associated with the batteries on the MFD electrical page?
White = Normal Amber = 50°- 65°C Red = Greater than 65°C (\_\_\_\_\_ BATT HOT and MASTER WARNING)
Where is the DC External Power receptacle and where does it connect to the electrical system?
Located on the forward left side of the nose and connects to the Left Main DC Bus.
When DC External Power is connected, can the APU DC Gen and/or DC GEN 1 & 2 run in tandem?
No. DC External Power prevents DC GEN 1 & 2 and the APU DC GEN from coming online while it is selected on.
Once the engines are started and the DC External Power is disconnected, how are the secondary busses powered prior to the AC GENS and TRU’s coming online?
Through the Main-Secondary Bus Ties
The EPCU provides automatic protection against DC External power malfunctions and will automatically take the DC External Power offline if the voltage goes over ____ or below ____.
Over 31 volts or below 22 volts
Where are the Engine Driven DC Starter Generators located and how are they cooled?
The DC Starter Generators are located on the engine accessory gearbox and are air cooled.
When does the Generator Control Unit switch the DC GEN from starter mode to generator mode?
After engine start and approximately 50% Nh the GCU will change the DC GEN from starter to generator and begin to power the associated Main Bus.
Will the EPCU automatically take a DC GEN offline if it overheats?
No. If the #1 DC GEN HOT or #2 DC GEN HOT Caution light is illuminated the QRH will direct the flight crew to turn off the associated generator. The main bus tie will close allowing one generator to power both main busses.
What do the Transformer Rectifier Units do and what do they power?
Convert 115vAC power from the AC Generators to 28vDC power for the secondary busses.
Where are the TRU’s located? How are they cooled?
Located in the upper right nose section and are air cooled.
Is there a switch to turn off the TRU’s?
No, only a circuit breaker on the 115 vAC panel located behind the co-pilot
Can the APU DC Generator provide power in parallel with the engine driven DC generators? Where does the APU Generator connect to?
Yes, on the ground the APU DC Generator can provide power to all of the main, secondary and essential busses by connecting to the right main bus and powering the others through the bus ties.
What happens if the EPCU detects a bus failure or fault?
It will automatically take that bus offline and reconfigure the bus ties to power the remaining busses.
When will the EPCU begin load shedding with multiple failures?
If there are two TRU failures along with a single DC GEN failure the EPCU will begin to shed non essential electrical loads.
What failures would lead to an electrical emergency and what does the EPCU do in that case?
If two DC GENs were to fail along with a single TRU then the EPCU will remove the ties from the batteries to the main busses, powering only the essential busses for approximately 45 minutes. The remaining TRU will also power the secondary busses.
Where are the 115vAC generators located? How are they cooled? What busses do they power?
The engine driven, oil cooled generators are mounted on the prop reduction gearbox. Each generator powers its respective variable AC BUS or if one fails, a single AC GEN can power the other bus and entire DC system through the bus cross tie (as long as the TRU’s are operational)
What components on the airplane are AC powered?
Windshield heating elements Ice detector probes #1 & #2 Pitot static tubes AOA vanes Engine Inlet Heating elements Standby Hydraulic Pump Auxiliary Fuel Pumps Propeller de-icing elements TRUs Galley Power
