B777 ElectricalHome / Quiz Page / B777 Electrical Boeing 777 Electrics Boeing 777 Electrics 1 / 15 Which condition(s) cause the ELEC GEN DRIVE L EICAS message to display? Generator drive oil temperature is high. GENERATOR CONTROL switch selected to OFF. Generator drive oil pressure is low. Either A or B is correct 2 / 15 The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the right transfer bus is not powered. False. True. The standby inverter converts DC power to AC power. The inverter powers the AC standby bus if the left transfer bus is not powered. 3 / 15 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. False. True. 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. 4 / 15 When will the RAT auto-deploy? Both transfer busses unpowered, both engines fail and C hydraulic system low Both transfer busses unpowered, and both engines fail. Both transfer busses unpowered, all three hydraulic systems low, both engines fail and C hydraulic system low Both transfer busses unpowered, all three hydraulic systems low, and both engines fail. 5 / 15 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. False. True. 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. 6 / 15 What is the electrical configuration during autoland? The left transfer bus isolates from the right transfer bus. There is no change from normal. The right transfer bus isolates from the right main AC bus. The left transfer bus isolates from the right main bus. 7 / 15 Which of the following is not a main AC electrical power source? Left and right engine integrated drive generators (IDGs). APU generator. Primary and secondary external power. Transformer Rectifier Units (TRUs). 8 / 15 What provides DC power on the B777? Transfer busses. Transformer rectifier units. DC generators. Standby inverters. 9 / 15 Which one of the following is not true about the ram air turbine (RAT) generator? The RAT can supply electrical and hydraulic power simultaneously. The RAT is deployed automatically if both AC transfer busses lose power in flight. The RAT cannot be manually deployed by pushing the RAM AIR TURBINE switch if any of the AC transfer busses powered. The RAT generator provides standby power to the C1 and C2 TRUs. 10 / 15 How can you power the ground handling bus before shutdown if no external power is available? Select the ground handling bus ON. Deploy the RAT. The bus is powered as long as the right main bus is powered. Start the APU. 11 / 15 Which one of the following is not true about the Secondary External Power? When the secondary external power source voltage and frequency are within limits, the secondary external power AVAIL (available) light illuminates. If the BATTERY switch is ON and no other source is powering the main busses, pushing the SECONDARY EXTERNAL POWER switch ON connects secondary external power to both main busses. Secondary external power can only power the left main bus. If a single IDG powers both main busses, pushing the SECONDARY EXTERNAL POWER switch ON connects secondary external power to both busses and removes the IDG source. 12 / 15 Which one of the following is not true about the backup electrical system? Right and Left backup generators power the converter at the same time. If both IDGs and the APU generator are inoperative, a backup generator powers essential airplane equipment to reduce electrical loading on the backup generator, some of the systems becomes inoperative such as TCAS, Centre tank override/jettison pumps (centre tank fuel is unusable). 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. 13 / 15 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? There is no automatic switching till the left engine is started. External power continues to supply the right main bus. The right engine generator powers both main busses. The right engine genrator automatically powers the right main bus. 14 / 15 The Electrical Load Management System (ELMS), manages load shed priority (galley first, utility bus second, then selected AC components). False. True. 15 / 15 What automatic switching will occur if you start the APU with external power on the BUS TIE system? The APU connects to the BUS TIE and replaces primary external power. The APU connects to the BUS TIE switches but does not power either main bus. The APU connects to the BUS TIE swıtches and powers the maın bus. The APU connects to the BUS TIE and replaces secondary external power on the left main bus. Your score is