Airframe Electrical midterm Flashcards
Give the three purposes of the primary battery in an aircraft application.
Ground ops (engine startup)
To absorb spikes from the generator/alternator
Emergency backup voltage
Name the two minimum controls necessary for any alternator.
Voltage regulator and current limiter.
What are the two batteries most widely used in aircraft application? Are they primary or secondary cells?
NiCads, lead acid, secondary cells.
State lenz’s law.
An induced emf always gives rise to a current whose magnetic field opposes the original change in magnetic flux.
What battery terminal must be disconnected first and reconnected last?
The negative terminal.
Name and explain the basis of the principles of operation of both generators and alternators.
Electromagnetic induction: electrical energy is produced by cutting lines of flux.
Name the four major components of a generator.
Field, armature, brush assembly, structural parts.
What principle is the operation of a generator based on?
Electromagnetic induction.
What does initial excitation in a generator come from?
It is provided by lines of flux produced by what is called “residual magnetism”
What are the three types of windings of a generator?
Shunt, series, compound.
What is excitation current?
The current passed through the electromagnet, used to produce, strengthen and control the flux field.
What is the purpose of the field in a DC generator?
To provide lines of magnetic flux for the conductor to cut through.
Describe the construction of a field in a DC generator.
Soft iron highly permeable cores called pole shoes are wrapped with copper wire (field windings), the pole shoes hold the windings in place.
What is the purpose of the armature in a generator?
It acts as a conductor, which cuts the lines of flux, into which the voltage is induced to produce current.
Describe the construction of the armature in a generator.
It consists of windings of wire called armature coil, multiple windings are used to increase the efficiency of the generator.
What is the armature in a DC generator known as?
A commutator, it is used to rectify the induced AC into pulsating DC.
What is the armature in an AC generator called?
In AC, slip rings are used to transfer the system current from the armature windings to be used by the system.
What is the purpose of the brush assembly in a generator?
To transfer the system current from the commutator to the housing wiring?
Describe the construction of the brush assembly in a generator.
Constructed of carbon and held against the commutator with springs.
Describe the construction of the structural parts of a generator.
Consists of an end frame, field frame, and a brush frame, bearings.
What are the three types of DC generators?
Series, shunt, compound.
What is an advantage/disadvantage associated with using a series wound generator?
It has higher output capabilities, it is very hard to control that output.
What is an advantage associated with a shunt wound generator?
It is easier to control output.
What is an advantage/disadvantage associated with using a compound wound generator?
Higher current and voltage output capability and is easy to control, more complex and heavier.
What are three controls for low output generators?
Voltage regulator, current limiter, RCCR.
What are three controls for a high output generator?
Voltage regulator, current limiter, RCCR.
What does RCCR stand for?
Reverse current cutout relay.
How is output controlled for an AC generator?
Voltage regulator, current limiter, RCCR.
What is an APU?
Auxiliary power unit.
What is the purpose of a CSD?
To take the rotational power from the engine and no matter the engine speed, turn the generator at a constant speed.
What is an IDG?
A CSD and generator combined into one unit.
What does IDG stand for?
Integrated drive generator.
What is the fundamental difference between an alternator and a generator?
The relationship between the conductor and the flux field.
What are the four major components of a DC Alternator?
Stator, rotor, rectifier, structural parts.
What is the purpose of the stator in an alternator?
It serves the same purpose as the armature in a generator.
Describe the construction of a stator.
Three stator windings, 120 degrees apart.
What are the two types of stator windings?
Delta, wye wound.
What is the purpose of the rotor in an alternator?
To provide lines of magnetic flux for the conductor to cut through.
Describe the construction of the rotor.
The rotor usually consists of 8-12 poles with windings around.
What is used to bring the excitation in an alternator rotor?
Brushes.
What is the purpose of a rectifier in an alternator?
It is used to convert AC to DC.
Describe the construction of an alternator rectifier.
Solid state (electronic) rectifier consists of 6 diodes, two for each winding.
What is the purpose of the structural parts in an alternator.
To support the stator and rotor.
Describe the construction of the structural parts of an alternator
Main frame, end frame, cooling fins.
Where does the alternator receive its excitation from?
The bus
What are two different devices used to control alternator output?
Voltage regulator and current limiter.
Alternator control units are usually in the form of what?
Solid state components.
What test is used for NiCad batteries?
High rate discharge test.
What tests are used on lead acid batteries?
High rate discharge test , load test , hydrometer test.
What does the high rate discharge test indicate?
The capacity.
What do the load test and hydrometer tests indicate?
State of charge.
How is flux produced in an alternator?
By the rotor.
How is flux produced in a generator?
By the field.
How is the system current produced in an alternator?
By the stator.
How is system current produced in a generator?
The armature.
Why are the brushes much smaller in an alternator?
They only need to carry excitation current.
Why are the brushes large in a generator?
They are necessary to carry system current.
What kind of rectifier is used in an alternator?
Solid state
What kind of rectifier is used in a generator?
Mechanical
What is one advantage of an alternator over a generator?
Physical size, since the rotating body of alternator is smaller, it can be turned at a greater rate. So it is capable of a greater output.
What are the three classifications of DC motors?
Series wound, shunt wound, compound wound.
What is an advantage/disadvantage associated with series wound DC motors?
Very high torque capabilities, very poor speed control.
What is an advantage/disadvantage associated with shunt wound DC motors?
Very good speed control, lower torque capabilities.
What is an advantage/disadvantage associated with Compound wound DC motors?
Relatively high torque capabilities with good speed control, heavier and more complex.
How is DC motor control obtained?
By controlling the flux field.
How is speed control obtained in a DC motor?
By controlling the strength of the flux field.
How is direction control obtained in a DC motor?
By reversing the polarity of the flux field.
What are two methods of reversing the direction of a DC motor?
Using a SPDT switch or by using a DPDT switch.
How is the direction of rotation of a DC motor changed?
By changing the polarity.
What are the different types of AC motors?
Universal, induction, synchronous.
What is an advantage/disadvantage associated with using a Universal AC motor?
High torque very versatile, loss of efficiency when used with AC higher maintenance.
What is an advantage associated with a synchronous AC motor?
Better speed control, higher torque capability than an induction motor.
What is a typical use for a universal AC motor?
Household applications, vacuums, drills etc.
What is a typical use for an induction AC motor?
Tachometer
What is a typical use for a synchronous AC motor?
Tape recorder.
What are the major parts of a DC motor?
Armature assembly,
Field assembly, brush assembly and end frame.
What is the principle the operation of a DC motor is based upon?
Electromagnetic repulsion.
What is the definition of electromagnetic repulsion.
The repulsion of an electromagnet by the pole of another electromagnet.
Shaft, laminated soft iron core, mica separators, armature windings, armature winding slots, commutator.
What are the parts of the large armature on the quiz?
What are the parts of the small armature on the quiz?
Field frame, pole shoes, field coils.
