EL126 Test 2 (DC Generators, Alternators, Inverters

What are some of the advantages that light aircraft DC alternators have over DC generators

Lighter, More efficient, can charge battery at low RPM

Where is the field winding of a light aircraft DC alternator located

In the Rotor

How is the field winding of a light aircraft DC alternator supplied with current

Via slip rings and brushes

Where is the armature of a light aircraft DC alternator located?

In the Stator

How is the output winding of a typical light aircraft DC alternator configured?

Three-Phase WYE-connected

What means is used to convert the AC output of a light aircraft DC alternator's output windings to DC

Rectifying Diodes

How many positive diodes are used in a typical light aircraft DC alternator, and where are they located?

3 in the internal heat sink

A generator is a machine that converts _____ energy into _____ energy

Mechanical , Electrical

the value of the induced EMF depends upon what three factors?

Strength of the Magnetic field, Speed of conductor relative to the field, angle at which conductor "cuts through" the field

to obtain a direct current output from a generator, a "rotating switch" or "mechanical rectifier" is fitted to the generator's armature/ what is the name most commonly used for this device?

Commutator

The output voltage of a DC generator is transferred from the commutator to the generator terminals using ______, which ride on the surface of the communtator.

Brushes

There are three types of DC generators, identified by the relationship of the field winding to the external circuit. What are they?

Series wound, shunt wound, compound wound

The ______ wound generator has such poor voltage regulation that it is never used as an aircraft generator.

Series

Medium duty generators used on aircraft are usually of the _______ wound type.

Shunt

Heavy duty DC generators will most often be of the ________ wound type.

Compound

A _______-_______ may be used on small turbine engines instead of separate starter and generator units.

Starter-Generator

________-_______ causes distortion in the magnetic field of the generator.

Armature Reaction

The ____-_____ is the position where the plane of the two opposite coils is perpendicular to the magnetic field of the generator

Neutral-Plane

A pole placed between the main poles of a generator to counteract some of the effects of armature reaction is called an __________.

Interpole

The direction of rotation of a generator may usually be found on the ______________

Data plate

On most large 28V generators, the positive armature lead in the generator connects to the ____ (B or E) terminal.

B

Regulation of the voltage output of a generator is accomplished by varying the strength of the _______ current.

Field

What are the three sections ("units") of a "Three-Unit" vibrator type voltage regulator?

Voltage Regulator, Current Limiter, Reverse-Current Cut-Out

In generator systems equipped with a "Three-Unit" vibrator type voltage regulator... if generator output voltage falls below that of the battery, which section of the regulator will disconnect the generator from the battery?

Reverse-Current Cut-out

Heavy duty generator systems will often use a _____-______ voltage regulator.

Carbon-Pile

In a carbon-pile voltage regulator, the pressure on the carbon stacks depends upon what two opposing forces?

An internal spring and and electromagnet

Name the four sections of a differential voltage reverse current relay (RCR).

Voltage Relay coil, differential relay coil, reverse current coil, main contactor relay

A low resistance, high power rating resistor installed in the "E" lead of an aircraft DC generator identifies this generator as part of a _____-lead paralleling system.

negative

The magnetism retained by the core of generator's field coils should be sufficient to produce a ________ _______ when the generator is turned at normal operating speeds.

small voltage

Residual magnetism may be restored by "________" the field.

Flashing

A "________" is used for testing the armature of a DC generator during overhaul.

Growler

If a generator's commutator is only slightly roughened, it may be smoothed using:

600 grit sandpaper or 000 sandpaper

How many "negative" diodes are used in a typical light aircraft DC alternator, and where are they located?

3 in the case of the alternator

What is the basic difference between a light aircraft DC alternator's "positive" and "negative" diodes?

Direction they allow current to pass.

Stem to Case: negative

Case to Stem: positive

Why do we not need a "Reverse Current Cut-Out" stage in a regulator used for a typical light aircraft DC alternator?

The diodes also provide a "check-valve" function, and will not permit the battery to discharge through the alternator

What two items or functions are usually included in a light aircraft DC alternator system which are not found in most automotive alternator applications?

Adjustable output voltage, and a means by which the alternator can be switched off (removed from aircraft bus)

Why is AC power preferred over DC for large aircraft power system applications

more efficient to produce, transform, and distribute.

also good for equipment that needs a constant speed

What is the usual unit of measurement used to specify the output power of a typical large aircraft AC alternator

Volt-Amps (VA) or Kilo-Volt-Amps (kVA)

What frequency value is most often associated with large aircraft AC power systems?

400 Hz

How many stator terminals are usually used on a typical large aircraft AC alternator?

6, however 3 are usually connected to ground

How are the stator windings of most large aircraft AC alternators configured?

Three-Phase WYE

Why are three-phase WYE configurations used for large aircraft AC alternators?

This configuration has two different output voltages from the same source

What advantage would there be in connecting the stator windings of an alternator in a "Delta" configuration as opposed to a "WYE" configuration

Current from each phase is 1.732 times that available from any separate phase

In most current-technology large aircraft AC alternators, how many brush assemblies are needed?

None

In most current-technology large aircraft AC alternators, what is the general function of the "PMG" section?

The PMG (Permanent Magnet Generator) is used to initially excite the alternator into operation, and its output is often used to power the electronic control devices for the alternator.

What is the name usually given to a unit consisting of a constant-speed drive transmission and a brushless AC alternator all in one package?

IDG (Integrated Drive Generator)

What would be the advantage of using an IDG instead of separate transmission and alternator?

Weight and Volume

In reference to aircraft power generating systems..... What is an inverter?

A machine or device that converts DC to AC

What are the two general types of inverters used in aircraft?

Rotary(Mechanical) and Static(Solid State)

In a rotary type inverter, why is a compound DC motor utilized?

to allow a series start and shunt operation

in order to increase the output frequency of a rotary type inverter.... what must be done to the compound motor's shunt field current?

Decrease it

Why is a rotary type inverter not usually started under load?

a rotary inverter doesn't produce the correct output frequency until it reaches the correct speed

What are the advantages of a static inverter vs rotary inverters?

Lighter, Quieter, More efficient, can be started under load.