AC Power Distribution

Question 1

The AC generators are connected to the what?

Answer 1

AC Busses

Question 2

AC Generators (often called alternators) are used as the primary source of electrical power on what type of aircraft?

Answer 2

almost all transport category aircraft

Question 3

Where DC is needed, what is used?

Answer 3

Rectifiers

Question 4

For emergency situations some aircraft can utilize what?

Answer 4

APU or a Ram Air Turbine (RAT). Inverters can also be employed.

Question 5

AC power can provide more what than a DC system?

Answer 5

power per weight of equipment

Question 6

Most AC generators require what?

Answer 6

Constant Speed Drive (CSD) to maintain a constant frequency

Question 7

The sole job of the CSD is to provide what?

Answer 7

constant 400Hz, regardless of throttle position.

Question 8

Proper oil level is critical for what?

Answer 8

proper oil temperature

Question 9

If a warning light comes on during flight, what should be done with the CSD?

Answer 9

disconnected immediately and inspected upon landing

Question 10

Early generators were composed of what?

Answer 10

a generator unit and a CSD

Question 11

The IDG contains both what?

Answer 11

the generator and the CSD in one unit

Question 12

What generator is similar to the basic IDG?

Answer 12

The Variable Speed Constant Frequency (VSCF) generator

Question 13

What happens to the RPM when dealing with the VSCF system?

Answer 13

The RPM of the drive and generator will change along with the engine.

Question 14

How does the VSCF maintain a constant frequency?

Answer 14

Thru the use of solid state components

Question 15

What does VSCF have located directly on the converter assembly?

Answer 15

BITE

Question 16

The output of the typical AC generator is 115 AC. This is converted by what?

Answer 16

Transformer-Rectifier Units (TRU) where DC is needed

Question 17

What is a TRU?

Answer 17

a step-down transformer and a full wave rectifier in one unit

Question 18

What is the TRU’s output?

Answer 18

28vdc

Question 19

What are two basic configurations used to distribute electrical power?

Answer 19

Split-buss system
Parallel system

Question 20

The split-buss electrical system contains what?

Answer 20

the completely isolated power generating systems

Question 21

When a generator fails, what happens to it?

Answer 21

the failed generator is isolated by the Generator Breaker (GB)

Question 22

What is one advantage of the Split-buss system?

Answer 22

that each generator operates independently

Question 23

Split-buss systems are more tolerant of what?

Answer 23

Frequency Variance

Question 24

Parallel systems require what?

Answer 24

strict operating limits

Question 25

What power distribution system has all AC generators connected to one distribution buss and maintains equal load sharing among all the generators?

Answer 25

Parallel

Question 26

In a Parallel system, should a generator fail, what happens to the failed unit?

Answer 26

The failed unit is isolated from the bus by the GB and flight continues using the remaining two generators to supply power.

Question 27

What are all generators synchronized and connected by?

Answer 27

The Tie Busses

Question 28

The busses are often referred to as what?

Answer 28

Synchronizing tie busses

Question 29

When closed, what does the Split System Breaker (SSB) do?

Answer 29

connects all generators together (paralleling the system)

Question 30

On modern aircraft with a parallel or split-parallel buss system, what is essential?

Answer 30

a centralized means of controlling power distribution between individual load busses is essential

Question 31

The power manipulation that happens between individual load busses must take place in a fraction of a second. To achieve this need, modern aircraft employ a what?

Answer 31

A solid State Buss Power Control Unit (BPCU)

Question 32

What does the BPCU do?

Answer 32

Receives data from the Generator Control Units (GCU's) and the various ties, busses, and breakers in the system. They are essentially small computers for a specific purpose.

Question 33

What are GCU's used for?

Answer 33

GCU's are used for each engine to monitor and regulate the generators output

Question 34

If a GCU detects a malfunction it will inform what?

Answer 34

The BPCU Which will then ensure the appropriate power distribution system configuration

Question 35

What does the SSB control?

Answer 35

Controls power between all generators or parallels all the generators and is controlled by the BCU's (BPCU's)

Question 36

The BPCU also receives what?

Answer 36

Input information from load controllers which sense real system current and provide control signals for the CSD or VSCF

Question 37

If a system fault occurs, what does the BPCU do?

Answer 37

initiates the corrective action and records the fault in a non-volatile memory

Question 38

What is a No-Break Power Transfer (NBPT)?

Answer 38

an incorporated system that can automatically change the AC power source without a momentary interruption of power

Question 39

Synoptic pages cover what?

Answer 39

a variety of critical aircraft systems that are important for the pilot and also for the technician to help with troubleshooting

Question 40

What do Synoptic pages provide?

Answer 40

they provide the viewer real time status data of the system and of the major components in the system