Electrical System Flashcards
The AC system is composed of:
(1) Two integrated drive generators (IDGs).
(2) One auxiliary power unit (APU) generator.
(3) One inverter.
(4) One ram air turbine (RAT).
(5) One AC external power unit.
The DC system is composed of:
(1) Two NiCd batteries.
(2) Three transformer rectifier units (TRUs).
(3) One DC external power input.
In the event of a power-generating source failure, ____ _____ automatically connect between the networks with no significant operational degradation or additional workload.
bus ties
IDG 1 AND IDG 2 SELECTOR KNOB
AUTO: allows automatic operation of the electrical system.
OFF: opens the IDG contactor isolating the IDG from the respective AC BUS.
DISC: must be held in this position for one second to mechanically disconnect the IDG.
NOTE The IDG fault indication LED associated with the EICAS message IDG 1 (2) OIL illuminates indicating to the flight crew which IDG must be disconnected (HOTLOP). The LED extinguishes after IDG disconnection.
APU GENERATOR BUTTON
PUSH IN: allows automatic operation of the electrical system.
PUSH OUT: opens the APU generator contactor and isolates the APU generator from the AC BUS TIE.
AC BUS TIES SELECTOR KNOB
1 OPEN: open the Bus Tie Contactor (BTC) 1, segregating AC BUS 1 from AC BUS 2.
AUTO: This position controls the operation of the BTCs, according to system operational logic.
2 OPEN: open the Bus Tie Contactor (BTC) 2, segregating AC BUS 2 from AC BUS 1.
GROUND POWER UNIT (GPU) BUTTON
PUSH IN: connects the AC GPU to the AC system, according to the source priority.
PUSH OUT: isolates the AC GPU from the system.
AVAIL: illuminates inside the button when the AC GPU is connected to the airplane and AC power quality requirements (voltage/amperage/frequency) are
satisfied.
IN USE: illuminates inside the button when the AC GPU is powering the airplane AC electrical system.
TRU ESS TOGGLE SWITCH
AUTO: allows automatic operation of the electrical system.
OFF: isolates the TRU ESS from the ESS BUS 3.
TRU 1 AND TRU 2 TOGGLE SWITCH
AUTO: allows automatic operation of the electrical system.
OFF: isolates the TRU from the respective DC BUS.
BATTERY 2 SELECTOR KNOB
AUTO: allows automatic operation of the electrical system.
OFF: the battery supplies power to the HOT BATT BUS 2 only and is no longer connected to the airplane electrical system.
DC BUS TIE TOGGLE SWITCH
AUTO: allows automatic operation of the electrical system.
OFF: opens both essential tie contactors (ETCs) and a DC tie contactor (DCTC).
BATTERY 1 SELECTOR KNOB
ON: the battery is connected to the DC ESS BUS 1.
OFF: the battery supply power to the HOT BATT BUS 1 only and is no longer connected to the airplane electrical
system.
When IDG oil pressure drops below ___ psi ± __ psi, or the IDG oil temperature reaches ___°F ± __°F (___°C ± _°C), the EICAS message IDG 1 (2) OIL is displayed and an amber LED illuminates near the IDG selector knob on the overhead panel. This LED indicates which IDG must be disconnected. Manual IDG disconnection is achieved by selecting and holding the respective IDG knob to the DISC position for ___ second.
NOTE Do not hold IDG knob to the DISC position for more than _____ seconds.
140 psi ± 25 psi
335°F ± 10°F (168°C ± 5°C)
one
three
both IDGs and the APU generator are rated at ___ VAC, ____ Hz, __ kVA ____phase.
115 VAC, 400 Hz, 40 kVA, three phase.
On ground, the APU AC generator or AC ground power unit (AC GPU) can supply power to all __ ____
AC BUSES
In flight, the RAT is used as an emergency generator, supplying power to the ___ _____ when both ______
ESS BUSES
AC BUSES 1 and 2 are not powered.
Integrated Drive Generator (IDG)
(1) Each engine has an IDG monitored and controlled by a dedicated _____. When an engine starts, the IDG will automatically come on line, powering the respective ____. The previous power source is disconnected from that AC BUS.
(2) For automatic operation of the electrical system, the IDG selector knob must be set to the AUTO position. Moving the selector knob to OFF position, the generator line contractor _______.
(3) Manual disconnection is achieved by selecting the respective knob to the
DISC position. The flight crew ____ reconnect the IDG
generator control unit (GCU)
AC BUS
opens, tripping off-line and deexciting the selected IDG
cannot
APU Generator
(1) Before engine starting, when the APU becomes available, the APU generator automatically connects to the _____.
(2) During the APU starting cycle, _____ is isolated from the network, powering the ______ exclusively. In flight, the APU can be started up within operational limits, and replaces any IDG sources with no operational degradation
AC BUS TIES, disconnecting the AC GPU
BATT 2
APU START BUS
The AC GPU button, located on the electrical system panel, controls the AC external power. Once the AC GPU is connected to the airplane and ________, an AVAIL light illuminates on the GPU button
Pushing the AC GPU button in connects external power to the ____, according to AC source priority. The AVAIL light extinguishes and an ____ light illuminates.
power quality requirements voltage/amperage/frequency) are within accepted limits,
AC BUS TIE
IN USE
Inverter
The static inverter (AC/DC inverter) converts _____ power from batteries to ____ power to supply the ______when an AC power source is not available.
28 V DC
115 V AC, 400Hz, single phase
AC STANDBY BUS
RAM Air Turbine (RAT)
(1) The RAT is an AC electrical device installed in the airplane nose section, which converts the kinetic energy of airflow across the turbine into AC power. The electrical power produced is rated at _____.
115 V AC, 400 Hz, 15 kVA, three-phase.
Whenever AC power sources are not powering ____, the RAT is automatically deployed, and after ___, supplies power to the ______. DC ESS BUSES are powered through the ____. To avoid total loss of power during this 8 s period, batteries are used as backup to power the ______
AC buses
8 seconds
AC ESS BUS
ESS TRU
DC ESS BUSES and the STANDBY AC BUS
The RAT electrical power drives the ____ for primary flight control tasks.
AC hydro Motor-driven Pump (ACMP 3A)
___ kt is required to ensure the RAT continues supplying _____. At speeds below this, the RAT may only supply the ___, and the batteries will automatically provide electrical power to the _____ through the static inverter (AC/DC inverter). As airspeed decreases, load shedding occurs and the ____ is no longer powered.
130 kt
AC/DC ESS BUSES.
AC ESS BUS,
DC ESS BUSES and the AC STANDBY BUS
AC ESS BUS
