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B767 Electrical System – Transcript
Video by AlexMaver · Watch the original on YouTube
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- For normal in-flight operations, electrical power is provided by two engine-driven generators and a third generator driven by the APU.
- When only one generator is available, low-priority items like the galleys automatically shut down to prevent overloads.
- If both main AC buses lose power, a hydraulic driven generator starts automatically to supply power to essential buses.
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for a normal in-flight operations all required electrical power is provided by two engine driven generators a third generator is driven by the Apu it is equal in size and capacity to either engine driven generator any two of these three generators meet all electrical requirements
with only one generator available some low priority items such as the galleys automatically shut down now let's operate the system let's begin with the airplane secured and external power disconnected
controls for the electrical system are located on the overhead panel with all electrical power Switched Off the main battery still continues to power items that require continuous power through the hot battery bus turn on the battery
the on indication in the battery switch appears the main battery discharge and Apu battery discharge lights indicate the batteries are being discharged and the battery bus is now powered now apply power to the standby system turn the standby power selector to auto
with standby power available the minimum essential instruments and systems necessary for safe flight are powered now let's connect ground power to the airplane the available light indicates external power is connected to the airplane and is of usable quality
the schematic on the right represents the functions of the electrical system panel now push the external power switch on the panel to connect external power to the main airplane electrical system the on light indicates external power is connected to the airplane's main electrical system the two main AC buses are distribution
points from which electrical power is distributed to all airplane systems the Apu generator can also power the main buses prior to engine start the Apu generator is available anytime the Apu is running
the Apu generator on enunciation indicates the switch is in the normal operating position and the generator breaker is armed for automatic operation push the Apu generator control switch to move it to the off position notice that the off light illuminates and the on indication disappears The off light also illuminates when the breaker
opens due to a fault situation that is covered in a later lesson return the Apu generator switch to the on position in this example the Apu is running and the Apu generator switch is on the Apu automatically Powers the main buses when external power is disconnected
connect the Apu generator to the system by disconnecting external power notice that Apu power replaces external power the external power on light extinguishes re-establish external power the only indication of the change from
Apu power to external power is the addition of the on enunciation in the external power switch each main engine generator in its Drive Unit are housed in a single case and share a common oil supply this
combined unit is called an integrated Drive generator or idg each idg is controlled by a generator control unit which provides automatic control functions and system protection the generator control switches automatically connect the idg to the main buses
the generator control switches remain in the on position for all normal operations in this position the on is in View and the breakers are armed for automatic operation the off-light illuminates when the breaker is open note this is different than the Apu switch which only illuminates with the fault or when the switch is turned off
now let's start the right engine the idg begins to rotate to operating speed
the generator breaker closes and the right generator off and drive lights extinguish the ride generator now Powers the right main bus at the same time external power automatically disconnects from the right bus and only supplies power to the left
main bus when the left engine is started the left bus tiebreaker opens and the left main bus is powered by its own generator
thank you the external power automatically disconnects from the tie bus and the Apu generator automatically connects to the tie bus
each main AC bus Powers one utility bus switches for the utility buses are located here for normal operation the bus tie switches are left in auto in Auto the bus tie Breakers keep both
main buses powered at all times from any available Source in a priority order the first priority is the associated engine generator when available second is the Apu generator and third is the opposite engine
generator external power is the only AC power source not automatically selected you must apply it manually note that both bus tie Breakers are open whenever the idgs are powering their respective buses push the left bus tie switch to position
it off notice the auto enunciation disappears and the isolation light illuminates the left bus tiebreaker is locked open with the switch off faults associated with the isolation lights are covered in another lesson however notice that even though the right bus tiebreaker is the right bus
tie isolation light remains extinguished the isolation lights always remain extinguished when the bus tie switches are in Auto and the bus tie Breakers are performing their normal automatic operation reset the left bus tie switch and notice that auto is again enunciated both engines are now running and both
engine generators are powering their Associated bus the only indication on the electrical panel is that the generator off lights and Generator Drive lights are extinguished the electrical panel is now configured for flight external power is disconnected notice in this normal
flight configuration all electrical panel lights are extinguished the Apu may be shut down the system uses two power sources to keep the buses powered unless only one power source is available
any one generator has sufficient capacity to supply all flight loads the airplane automatically performs a load shed to prevent overload or to reduce an existing overload condition if only one power source is available load shedding removes non-flight related
loads the galleys and utility buses are automatically removed the utility buses power passenger entertainment systems and recirculating fans if an overload condition occurs
first all galleys are shed and then the associated utility bus
now look at the automatic switching that takes place during the normal shutdown procedure you have arrived at the ramp the Apu is running and external power is available let's shut down the left engine when the fuel control is moved to cut off the idg disconnects
the engine generator breaker opens the left bus tiebreaker closes and the Apu Powers the left bus the right bus is still powered by the right engine generator when the right engine is shut down the right bus tiebreaker closes and the Apu automatically Powers the right main bus
to keep the main buses powered select external power prior to Apu shutdown notice that external power now Powers the right main bus and the left main bus now turn the Apu off