AT 265 Final Exam Unit 3

Armature negative is typically connected to the

generator case (GROUND)

Reverse Current Relay

prevents reverse current flow To the generator from the battery

Virtually all generators employ some type of ______ system

regulation

What allows for the brushes to be smaller and carry a lower current

the field rotates

All generators (including DC) produce what type of current?

AC

Why do we need a reverse current relay?

If current is fed to both the field and armature winding it will motorize the generator It would discharge the battery if generator malfunctioned

Equalizing Circuit

Keeps voltage within limits on 2 generator systems

All generators produce what?

Alternating current

The armature winding

Carries high current Typically 3 phases 120 degrees apart

The field winding

Carries low current Receives voltage from the regulator Connected through brushes and _______________

The rectifier

Changes AC to DC

What does the process of electromagnetic induction do?

Changes mechanical energy into electrical energy.

Regulator

Controls field strength Keeps generator output at the necessary voltage and current for any flight or load variable

How do you flash the field?

Disconnect the voltage regulator Send current through generator field winding

Brushes

Electrical contacts which touch the commutator and provide a current path for the power to leave the rotating armature

What is the most common repair on a DC generator?

Brush replacement

Compound Wound Generator

Has two field windings; one in parallel and one in series with the armature and the load.

Can and A&P technician rebuild a generator?

NO

Commutator

Part of the rotor which connects the armature winding to the generator brushes. Used to change AC to DC

What is the purpose of a DC generator on an aircraft?

Charge the battery Send power to electrical loads

Field Winding

The electrical winding which creates the magnetic field needed for electromagnetic induction. Stationary and is an electromagnet

Series Wound Generator

The field coil is in series with the armature and the load

When the relay points of the vibrating regulator are closed:

field connected to full voltage full field current full generator output

When the relay points of the vibrating regulator are open:

field is connected to voltage through a resistor lowers field current lowers generator output

Current limiter

limits the generator output current

What materials typically make up the commutator?

pure copper with an insulation between each segment

On most DC generators the F terminal is

the field negative connection

Armature

the main current carrying electrical winding rotates and receives (produces) the induced current/voltage

Rectification

the process of converting AC to DC

The strength of the induced current/voltage depends on:

the strength of the magnetic field the number of turns in the conductor coil the speed of motion between the magnet and the conductor

The Vibrating regulator has 3 units:

voltage regulator current limiter reverse current relay

Reverse current relay section of a vibrating regulator:

Voltage coil winding & current coil winding

Generator

a device that converts mechanical energy into electrical energy. Usually a main power source or produce power for a specific system

Most DC generators are wound how?

in PARALLEL

DC Alternators change _____ energy into _____ energy

mechanical electrical

A full wave rectifier has how many silicon diodes?

6

Theory of operation for a carbon pile generator?

A stack of carbon discs control field current Resistance of the carbon stack varies inversely with pressure applied to the stack An electromagnet controls the pressure on the stack Electromagnet is wired in parallel to generator output

What does an aircraft typically get powered on?

DC current

In a vibrator type voltage regulator, how are the contact points opened and closed?

Electromagnet

Magnetic field strength is a function of:

FIELD CURRENT

In a series wound generator, what happens when the LOAD increase?

Field current and generator output INCREASE

In a DC alternator, which is the rotor and stator?

Field winding rotates Armature winding stationary

If Residual magnetism is lost what should we do?

Flash the field

DC alternators produce __ in the armature and change it to __ before it leaves the alternator

AC DC

Basic regulator theory?

ALL voltage/current regulation is achieved by varying the strength of the magnetic field.

Can an A&P repair and rebuild an alternator?

NO, only repair

What are the types of generators?

Series, Parallel (shunt), and compound wound generators

What allows for longer brush life since slip rings are smooth and not rough?

Slip rings provide the electrical connection to the _______________

In a compound wound generator, what happens when the LOAD increases?

The SERIES field current DECREASES The PARALLEL field current INCREASES Generator output CONSTANT

What allows the armature output to be connected directly to the rectifier and not through the brushes?

The armature is ____________________

Electromagnetic Induction

The basic principle for the operation of every generator. The process of producing voltage (current) by moving a conductor (wire) through a magnetic field

In a parallel wound generator, what happens when the LOAD increases?

The field current and generator output DECREASE

Parallel (shunt) Wound Generator

The field winding is in parallel with the armature and the load.

Residual Magnetism

The small amount of magnetism retained by the generator field. Needed to close the reverse current points

What are the two types of alternator regulators>?

Vibrating contact points --> mechanical Transistorized --> solid state

Voltage Coil Winding

Wired in parallel WRT generator output Is needed to initially close the reverse current points

Current Coil Winding

Wired in series WRT generator output Needed to keep the contact points closed during normal system operation

Can an A&P technician repair a generator?

YES

Voltage regulator

controls system voltage

What does a DC generator typically contain?

Armature, field, commutator, brushes

What are three common types of regulators?

Carbon Pile Vibrating Contact Solid State

The voltage regulator section of a vibrating regulator:

Contains a relay wired in parallel WRT generator output called a voltage coil

The current limiter section of a vibrating regulator:

Contains a relay wired in series WRT generator output called a current coil