Boeing B787 - Electrical
Each generator has a drive disconnect mechanism that allows the generator to be mechanically disconnected from the engine. Depending on the fault condition, the generator drive is:
Four engine driven PMA - Permanent Magnet Alternators (two per engine) are the primary source of power for the EEC. PMAs are independent from the main airplane electrical system, and are also independent from each other.
There are (only) two engine driven Permanent Magnet Alternators (PMA) (one per engine).
What elements indicate a condition that requires the flight crew to disconnect the generator drive?
_____ is used for APU start if an engine is running or forward external power is selected ON.
The APU has two 235 Vac variable frequency starter/generators, designated left (L) and right (R). The generators are directly connected to the APU gearbox, producing variable frequency power proportional to APU speed.
Amongst the different sources of electrical power, the B787 uses:
The other electrical system power sources are three external AC power receptacles, one Ram Air Turbine (RAT), one main battery, one APU battery, three flight control Permanent Magnet Generators and two EEC Permanent Magnet Alternators.
The power sources remain isolated from each other throughout the generation and distribution channels. During power transfers, a brief power interruption may occur as buses are energized from a new power source.
An engine is started using two electric starter units and once running they are used as VFSG (Variable Frequency Starter Generators) that power four AC buses. Except for engine anti-ice, the B787 doesn't have a bleed air system.
Electrical power for engine start can be provided by external power, APU generated power, or the opposite engine’s generated power. What is the true statement?
The B787 electrical system primarly uses VAC (Volts Alternating Current) and VDC (Volts Direct Current):
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Electrical power for APU start can be provided by:
For APU starts with the APU battery as the power source (no engine running and forward external power not ON), the left starter-generator is always used.
For APU starts with the APU battery as the power source (no engine running and forward external power not ON), the right starter/generator is always used.
_____ engine driven Permanent Magnet Generators (PMG) are the primary source of power for the flight control electronics. These power sources are independent from the main airplane electrical system, and are also independent from each other.
A secondary source for flight control power is provided by the airplane’s 28 Vdc bus distribution system, and the main battery. In addition, a backup system is provided by dedicated batteries to assure positive flight control operation during temporary power interruptions.
If the APU battery experiences a severe failure and overheats, a sealed enclosure ensures the resulting heat and gases are contained so they pose no hazard to the airplane or its occupants.
This is also true for the main battery.
The B787 is equipped with a "Towing Power Mode" that makes possible to be towed without powering up the CCS (Common Core System). How does it work?
Radio communication systems are not energized in the towing power mode.
After engine start, what is the function of the starter-generators?
In addition of the PMAs - Permanent Magnet Alternators, a secondary source for EEC power is provided by the airplane’s 115v AC bus distribution system. The AC bus distribution system provides:
Each generator has a drive disconnect mechanism that allows the generator to be mechanically disconnected from the engine. If automatically disconnected, it can be reconnected once by the flight crew, if manually disconnected the drive cannot be reconnected by the flight crew.
Whatever the disconnection is, the drive cannot be reconnected by the flight crew.
The generator DRIVE light, generator DRIVE synoptic indication, and EICAS advisory message ELEC GEN DRIVE shows when a condition is detected that requires the flight crew to disconnect the generator drive.
The generator can then be disconnected from the engine by pushing the respective generator drive disconnect (DRIVE DISC) switch. The drive cannot be reconnected by the flight crew.
What are the specifications of the variable frequency starter - generators?
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The engine starter - generators function as electrically powered starter motors for engine start, and as engine driven generators once the engines are running. Each engine has two 235 Vac variable frequency starter/generators. L1 and L2 are mounted on the left engine. R1 and R2 are mounted on the right engine.
They are directly connected to the engine gearboxes, producing variable frequency power proportional to engine rotor speed.
What is the meaning of the amber cross in this electrical synoptic?
this is an engine generator synoptic Indication, not an engine drive one!
The APU battery provides power on the ground for:
The electrical power sources remain isolated from each other throughout:
A Ram Air Turbine (RAT) serves as an emergency source of electrical and hydraulic power. It has no operating time limits, airspeeds, or altitudes.
DRIVE fault symbol and engine generator drive disconnected symbol appear together when drive is disconnected.
Generator status is shown by generator switch indications, MFD electrical synoptic, and the EICAS message system.
Towing Power Panel - if you push the TEST switch, the applicable towing battery charge light illuminates, indicating the current state of charge of the batteries (HIGH, MEDIUM, LOW). If you see a white "LOW" indication, what does it indicate?
Minimum times assume steady state towing (no braking) before batteries are depleted. If heavy braking occurs, actual time remaining may fall below the minimum times listed.
What does this Forward External Power Synoptic Indication mean?
The B787 electrical system primarily uses 115 Vac and 28 Vdc power, with a limited number of systems optimized with 235 Vac.
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What does this Main Bus Synoptic Indication mean?
What provides power if there is a total loss of electrical power in flight?
A Ram Air Turbine (RAT) serves as an emergency source of electrical and hydraulic power.
In flight, the RAT deploys automatically if any of the following occur:
The RAT can be deployed manually if necessary by pushing the RAM AIR TURBINE switch on the hydraulic panel.
The RAT can be deployed manually if necessary by pushing the RAM AIR TURBINE switch on the electrical panel.
The RAT can be deployed manually if necessary by pushing the RAM AIR TURBINE switch on the HYDRAULIC panel.
The B787 has:
The APU battery functions automatically, and has no flight deck power switch. Operating indications for the main and APU batteries are provided on the electrical synoptic.
What does this Engine Generator Synoptic Indication mean?
