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Atlas Aircw 777 > Electrical System > Flashcards

Electrical System Flashcards

1
Q

When does the backup AC electrical system automatically supply power to one or both transfer busses?

A

• only one main AC generator (includes APU) is available
• power to one or both of the main AC busses is lost
• approach (APP) mode is selected for autoland

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2
Q

When is the back up system tested?

A

The system is automatically tested after engine starts and transfers power without
interruption

6.20.7

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3
Q

Where does the primary power come from for the flight control DC electrical system?

A

Primary power for the flight control DC electrical system comes from permanent
magnet generators (PMGs) housed within each backup generator

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4
Q

Where do the PSA’s get their backup power?

A

secondary power for the left
and right PSAs is provided by the related main DC bus. (LT and RT main DC busses)
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

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5
Q

What are the components for the Standby Electrical system?

A

The standby electrical system consists of:
• the main battery
• the standby inverter
• the RAT generator and its associated generator control unit
• the C1 and C2 TRUs.

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6
Q

The standby Inverter converts DC power to AC power, what buss does it power and when?

A

The inverter powers the
AC standby bus if the left transfer bus is not powered.

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7
Q

What components make up the DC electrical system?

A

The DC electrical system includes:
• main DC electrical system
• batteries
• battery chargers
N704GT - N710GT
• towing power
• flight control DC electrical system

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8
Q

How many TRUs are there? What are they called? And what busses power them?

A

The main DC electrical system uses four transformer–rectifier units (TRUs) to
produce DC power. The TRUs are powered by the AC transfer busses.

Lt TRU, C1 TRU, is powered by the Lt transfer buss

Rt TRU, C2 TRU, is powered by the Rt transfer buss

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9
Q

What is the purpose of the ELMS (Electrical Load Management System)?

A

The ELMS provides load management and protection to ensure power is available
to critical and essential equipment

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10
Q

How does ELMS manage the aircraft electrical load?

A

ELMS
automatically sheds AC loads by priority until the loads are within the capacity of
the airplane or ground power generators

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11
Q

What order does ELMS shed electrical load? And what order does ELMS restore the load?

A

The load shedding is galleys first, then
utility busses. Utility busses are followed by individual equipment items powered
by the main AC busses

The shed systems are restored in reverse order

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12
Q

How does ELMS help manage center fuel tank fuel?

A

The ELMS also provides inputs for display of EICAS messages for manual center
tank fuel pump shut off during climb/cruise, and automatic shut off to prevent
unintentional dry fuel pump operation when the center fuel tank is empty

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13
Q

What are the main AC electrical power sources?

A

The main AC electrical power sources are:
• left and right engine integrated drive generators (IDGs)
• APU generator
• primary and secondary external power.

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14
Q

How are the normal power sources (IDG, APU, External power) operated? And how is power transferred between power sources on the ground?

A

The power sources normally operate isolated from one another.

During power source transfers on the ground (such as switching from the APU generator to an
engine generator) operating sources are momentarily paralleled to prevent power
interruption.

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15
Q

What happens when the IDG (Integrated Drive Generator) comes on line?

A

When an engine starts, with the GENERATOR CONTROL switch selected ON,
the IDG automatically powers the respective main bus. The previous power source
is disconnected from that bus

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16
Q

In what ways can the IDG be disconnected form the main AC busses?

A

The IDG can be electrically disconnected from the busses by pushing the
GENERATOR CONTROL switch to OFF.

The IDG can also be electrically
disconnected from its respective bus by selecting an available external power
source prior to engine shutdown.

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17
Q

What cause the DRIVE light to illuminate and the EICAS message ELEC GEN DRIVE L or R to display?

A

low oil pressure is detected in an IDG

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18
Q

Can the IDG DRIVE be disconnected and if so how? Is this action reversible in flight?

A

The IDG drive can be
disconnected from the engine by pushing the respective DRIVE DISCONNECT
switch.

The IDG cannot be reconnected by the flight crew

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19
Q

What cause the IDG to disconnect automatically?

A

High drive oil temperature causes the IDG to disconnect automatically.

20
Q

What is the function of the APU generator?

A

The APU generator is electrically identical to the IDG generators.

The APU generator can power either or both main busses, and may be used in flight as a
replacement to an IDG source

21
Q

What is the relationship between the APU and external power?

A

APU take priority over the Secondary external power

APU and primary external together, APU powers the Lt AC main bus and external power powers the Rt AC main bus.

The APU can power both main AC busses when the only power source.

6.20.2

22
Q

What does the APU generator OFF light illuminates mean?

A

when the APU is operating and the APU
generator breaker is open because of a fault or the APU GENERATOR switch is
selected OFF

23
Q

In flight, when does the APU come on automatically?

A

when both transfer busses are unpowered, the APU starts automatically,
regardless of APU selector position

24
Q

How is AC Electrical power distributed?

A

AC power is distributed through the left and right main busses, ground handling
bus, and the ground service bus.

25
Q

How do the BUS TIE switches work?

A

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.

26
Q

While on the ground power transfers are made without interruption, what is one exception?

A

when switching between primary and secondary external power sources

27
Q

What is the course order for powering the Lt and Rt main AC busses, while in flight?

A

• respective IDG
• APU generator
• opposite IDG

28
Q

Each main bus also powers its associated busses, which are?

(typical loads are shown in
parentheses)

A

• transfer bus (DC system transformer–rectifiers, AC standby bus)
• utility bus (forward galley heater, chiller boost fan, gasper fan, captain’s
and first officer’s foot and shoulder heaters, door area heaters, lavatory
water heaters and shavers)
• galley busses.

29
Q

What is the main source of power for the Ground Service Bus? What is the alternate source of power?

A

Normally powered by the Right Main AC Bus

Alternate sources:
• the APU generator
• primary external power

30
Q

What does the GROUND SERVICE BUS power?

A

The main batter charger

The APU battery charger

miscellaneous cabin and system loads

31
Q

What powers the GROUND HANDING BUS?

A

The ground handing bus can only be powered by the APU generator or

from the primary external power source

32
Q

What Items dos the GROUND HANDING BUS provide power too?

A

Cargo handling

Fueling and refueling operations

And other equipment energized only during ground operations.

33
Q

How is the electrical system isolated during an autoland?

A

• 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 main DC bus, and the first officer’s flight instrument bus

34
Q

How is backup power provided?

A

Backup power is provided by one variable speed, variable frequency generator mounted on each engine

35
Q

What is the purpose of the converter and how many backup generators can power the converter at one time?

A

The converter converts the backup generator frequency to a constant 400hz

Only on backup generator can power the converter at a time

36
Q

How many PMG (permanent magnet generators) are there? Where are they housed and what do they power?

A

Each backup generator contains two permanent magnet generators (PMGs) that
supply power to the flight control DC electrical system

37
Q

How is the Lt TRU DC electrical power distributed?

A

The left TRU powers the left main DC bus, which provides a second DC power
source for:
• left flight control power supply assembly (PSA)
• right main DC bus.

38
Q

How is the Rt TRU power distributed?

A

The right TRU powers the right main DC bus, which provides a second DC power
source for:
• right flight control PSA
• left main DC bus.

39
Q

How is the C1 TRU power distributed?

A

The C1 TRU powers the captain’s flight instrument bus and the battery bus. The
captain’s flight instrument bus provides a second DC power source for:
• center flight control PSA
• first officer’s flight instrument bus

40
Q

How is the C2 TRU power distributed?

A

The C2 TRU powers the first officer’s flight instrument bus, which provides a
second DC power source for the captain’s instrument bus.

41
Q

How does towing power work?

A

Permits towing operations without AC power. With the TOWING POWER switch selected to BAT position, main battery power is provided through the hot battery bus to systems required for towing.

When AC power is applied to the airplane and
the TOWING POWER switch is in BAT, the main battery provides back-up if AC
power is lost during towing

42
Q

Each Power Supply Assemblies (PSA) has a dedicated battery for what purpose?

A

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

43
Q

The Standby Electrical system can supply AC and DC power and is made up of what components?

A

The standby electrical system consists of:
• the main battery
• the standby inverter
• the RAT generator and its associated generator control unit
• the C1 and C2 TRUs.

44
Q

The Main Battery provides standby power to what?

A

The main battery provides standby power to the:
• hot battery bus
• battery bus
• captain’s flight instrument bus
• left and center flight control PSAs
• standby inverter

45
Q

When is the RAT automatically deployed?

A

if both AC transfer busses lose power in flight

46
Q

What system are turned off when the CABIN/UTILITY switch is turned off.

A

• ground service bus, except:
• main and APU battery chargers
• left forward fuel pump
• utility busses
• galley
• gasper fan

• beacon, logo, and wing lights
• main deck cargo, lower forward cargo, lower aft cargo compartment
electrical power outlets
• supernumerary general lights
• main deck alert system, and
• in flight, main deck cargo lights.

47
Q

What system are provided powder when the CABIN/UTILITY switch is OFF?

A

• night and supplemental night lights
• reading lights
• some galley and crew rest lights

Atlas Aircw 777 (7 decks)

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