*
P200 Right power panel
*
P300 Auxiliary power panel
*
P110 Left power management panel
*
P210 Right power management panel
*
P310 Standby power management panel
*
P320 Ground service/handling power panel.
Main and backup power go to the left, right, or auxiliary power panels. These power panels supply power to large loads (25 amps or more). They also supply power to the power management panels and the ground service/handling power panel. From these panels, electrical power goes to small loads (less than 25 amps).
The ELMS power management panels contain line-replaceable units. These control and monitor the load-switching devices in their related ELMS panels. However, the ELMS line-replaceable units do not control all of the large load-switching devices in the power panels. The GCUs, BPCU, and backup generator converter directly control some of the large load-switching devices.
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The line-replaceable units get data from the other electrical power control units and airplane systems either directly or from the ARINC 629 system buses. They use this data to manage the loads of the electrical power system.
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General
The electrical power system normally operates as two independent power channels: left and right. These buses are on the left channel:
*
Left main ac
*
Left utility
*
Left transfer
*
Left dc
*
Standby ac
*
Captain’s flight instrument
*
Battery
*
Battery #2.
The left channel also supplies power to the left and center flight controls dc power supply assemblies (FCDC PSA).
These buses are on the right channel:
*
Right main ac
*
Right utility
*
Right transfer
*
Right dc
*
First officer’s flight instrument
*
Ground service
*
APU battery
*
Hot battery.
The right channel also supplies power to the right FCDC PSA.
Power Configurations
The buses may connect to different power sources and to each other. This depends upon which power sources are available, the flight phase of the airplane, and the configuration of the flight deck electrical panel. Breakers, contactors, and relays connect the buses to the power sources and to each other.
Ground Power
Primary external power automatically supplies power to the ground handling buses. You can also use a switch to connect primary external power to the ground service bus. When you turn primary external power on at the electrical panel, the power connects to the right main ac bus. From there, it supplies power to the rest of the electrical system.
If you need more ground power capacity, connect the secondary external power. The right bus tie breaker (BTB) opens so that the secondary external power supplies power to the left side of the electrical system while the primary supplies power to the right side.
APU Power
The APU generator can supply power to the airplane on the ground or in flight. On the ground, it can supply power to the ground handling bus. The APU generator can also supply all of the airplane power or share the load with an IDG, backup generator, or the primary external power source.
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IDG Power
The IDGs normally supply the electrical power when the engines are operating. They each supply power to one side of the electrical system. If an IDG fails, the APU generator can supply power to the failed side.
Backup Generator Power
The backup generators are a variable-speed, variable-frequency type. They operate when the engines are running. They connect to the backup generator converter. The converter makes the backup generator output into satisfactory ac power. A backup generator supplies power to a transfer bus under non-normal conditions and during autoland.
Each backup generator also contains permanent magnet generators (PMGs). Two of these PMGs in each backup generator are the primary power sources for the FCDC PSAs.
Standby Power
If all normal power is lost, the RAT generator can supply the flight instrument buses with power. It does this through the two center transformer rectifier units (TRU). The captain’s flight instrument bus then supplies power to the battery and standby ac buses.
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