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
