The Electrical Load Management System (ELMS), manages load shed priority (galley first, utility bus second, then selected AC components).
Which one of the following is not true about integrated drive generators (IDGs)?
How are the busses powered if the right engine is started with the APU powering the left bus system and external power powering the right bus system?
Which bus operates only on the ground?
Bus tie relays, controlled by BUS TIE switches, isolate or parallel the right and left main busses. When both BUS TIE switches are set to AUTO, the bus tie system operates automatically to maintain power to both main busses.
How can you power the ground handling bus before shutdown if no external power is available?
What is the primary source of DC power during normal flight?
Which one of the following is not true about the Primary External Power?
What is the secondary source of power for 'fly-by-wire' if one or more PMGs are unpowered?
When will the RAT auto-deploy?
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What is the correct electrical panel configuration for normal flight?
What provides DC power on the B777?
Which one of the following is not true about the DC electrical system?
Which one of the following is not true about the flight control DC electrical system?
Which one of the following is not true about the standby inverter?
What is the primary power source for 'fly-by-wire'?
Which one of the following is not true about the ram air turbine (RAT) generator?
Which condition(s) cause the ELEC GEN DRIVE L EICAS message to display?
Which one of the following is not a reason for the backup electrical system to automatically power one or both transfer busses?
Does electric power has priority over hydraulic power from the RAT?
Hydraulic has priority, and if electric is shed, only the CA instrument bus is powered through the main battery
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What is the correct source order for powering left and right main busses in flight?
Which one of the following is not true about the APU generator?
What automatic switching will occur if you start the APU with external power on the BUS TIE system?
Which of the following is not a main AC electrical power source?
What is the primary source of power for the transfer busses?
How many main AC power sources are required to maintain the entire plane AC electrical load?
Which bus powers the main battery charger and the APU battery charger?
Which one of the following is not true about the backup electrical system?
On ground no power connected to the airplane. Which items will be powered if you push the BATTERY switch ON?
How many total AC sources of power does the B777 accommodate?
Seven (2 IDG, APU, PRI and SEC external power, 2 BUG).
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The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the right transfer bus is not powered.
The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the left transfer bus is not powered.
Which one of the following is not true about the Secondary External Power?
What is the primary source of standby power if all normal AC and DC power source fail?
Backup power is provided by one variable speed, variable frequency generator mounted on each engine. A frequency converter converts the generator frequency to a constant 400 Hz. Only one backup generator can power the converter at a time.
The main battery provides standby power to the following:
When does the right transfer bus isolate from the right main bus?
What does the green EXTERNAL POWER AVAIL light indicate?
The standby electrical system consists of:
Primary power for the flight control DC electrical system comes from permanent magnet generators (PMGs) housed within each backup generator. Variable frequency PMG AC power is used by individual power supply assemblies (PSAs) to provide DC power to the three flight control DC busses. To ensure a high level of system reliability, each PSA also has multiple AC power sources.
To ensure a high level of system reliability, each PSA also has multiple DC power sources (No AC power!). If primary PMG AC power is not available, secondary power for the left and right PSAs is provided by the related main DC bus. Secondary power for the center PSA is provided by the captain’s flight instrument bus. The hot battery bus provides additional backup power for the left and center PSAs only. Each PSA also uses a dedicated battery to prevent power interruptions to the related flight control DC bus. The batteries have limited capacity and are incorporated to supply power for brief periods during PSA power source transfers.
During autoland, the busses isolate to allow three independent sources to power the three autopilots.
The left IDG powers the left AC transfer bus, the left main DC bus, and the captain’s flight instrument bus The right IDG powers the battery bus and AC standby bus through the main battery charger The backup system powers the right AC transfer bus, the right DC bus, and the first officer’s flight instrument bus.
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What is the electrical configuration during autoland?
If the RAT is unable to maintain RPM, the RAT generator electrical load is shed until RPM is satisfactory. Power for standby electrical loads is provided by the main battery during deployment of the RAT and when RAT generator loads are shed.
The RAT is deployed automatically if both AC transfer busses lose power in flight. The RAT can be manually deployed by pushing the RAM AIR TURBINE switch on the overhead panel.