Defenitions And More Flashcards
Electron flow theory flow from:
-negative to positive
-positive to negative
Negative to positive
Do lines of flux flow from:
-north to south poles
- south to north poles
North to south
Where are magnetic lines of flux most densely concentrated at?
North and south poles
What is electromagnetism?
Current flowing through a conductor creates a magnetic field
What are three factors that determine the strength of an electromagnet?
-amount and type of conductor
-magnetic strength of core material
-Amount of current flow
What is a materials ability to become magnetized known as?
Permeability
What is a materials resistance to become magnetized knows as?
Reluctance
What is magnetism left in a material known as?
Residual magnetism
What are two types of magnets?
Permanent magnet
Electromagnet
What type of DC machine converts, electrical energy to mechanical energy?
Dc Motor
What type of DC machine converts, mechanical energy to electrical energy?
DC generator
What are six common DC machine components?
Enclosure
Pole pieces
Field windings
Armature assembly
Brushes
Terminals
What is the rotating assembly of a DC machine called?
Armature
What type of field windings have many terms of small gauge wire?
Shunt field windings
What type of field windings have fewer turns of large gauge wire
Series field winding
What components of a DC generator converts AC to DC?
Commutator
What is the purpose of field windings in a DC machine?
To create magnetic lines of flux
What are three basic types of amateur windings?
-Lap wound (low voltage, high current)
-Wave wound (high voltage, low current)
-Frog leg wound (moderate voltage and current)
What are two types of bearings?
Sleeve and ball
Roller
What keeps the brushes pressed against the commutator?
Brush holder and springs
What part of a DC machine supports the shaft and allows it to rotate?
Bearings
Why are some pole pieces curved?
To allow for a wider and more even flux distribution
What two materials can brushes be made of?
Carbon or graphite
What are three types of field windings in DC machines?
-Series
-shunt
-compound
What are the shunt field winding terminals labeled?
F1 and F2
What are the series field winding terminals labeled?
S1 and S2
What is the mechanical force used to turn a generator?
Prime mover
What are four components of an armature assembly?
-Shaft
-Iron core
-commutator
-armature windings
What separates the sections of copper on a commutator?
Mica insulation
What are four types of enclosures?
Open type
Weatherproof
Drip proof
Totally enclosed
According to electron theory, does current flow through an energy source from the positive to the negative terminal?
Yes
What’s a DC generator that uses permanent magnets as its field known as?
Magneto
What is the portion of the pole piece closest to the armature called?
Pole shoe
When proper commutation is taking place, what colour is the commutator?
A dark chocolate colour
Typically, which three terminal leads are positive in polarity?
A1
S1
F1
How can the ripple effect be smooth in the output of a DC generator?
Increasing the number of windings in the armature
What are three types of DC machine field structures?
Permanent magnet
Separately excited
Self excited
When a DC generator contains both series and shunt field windings, what is it called?
A compound generator
What are three factor factors that determine the output of a generator?
Magnetic field strength
Number of conductors in the armature
The speed at which the armature is driven
When a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor. What is the principal called?
Electromagnetic induction
What is the position at which the armature windings are parallel to the lines of flux and there are no induced voltage called?
Neutral plane
What two magnetic fields interact to cause the amateur to rotate in a DC motor?
One created by the current in the amateur winding
One created by the current in the field windings
What is the force that causes a motor to rotate known as?
Lorentz force
What are the windings embedded in slots or holes in the main pole faces called?
Compensating windings
Is the voltage induced into the armature windings of a DC generator AC or DC?
AC
What is the distortion, or bending, of the main magnetic field of a DC machine, caused by its interaction with the magnetic flux developed by the armature current called?
Armature reaction
How is the windings of an Interpol connected in relation to the armature?
In series with the armature
When a generator supplies current to a load, what is produced, which makes the armature assembly harder to turn?
Counter torque or motion action
What happens to counter EMF generated as a load is added to a series motor?
CEMF increases
What are three ways armour reaction can be corrected?
Rotate the brushes
Interpose and commutating windings
Compensating windings
True or false
The interpose of a DC motor will have the same polarity as the main field poles directly behind them in the direction of rotation ?
True
What are two main factors that affect the amount of torque developed in a DC motor?
Strength of the magnetic field
Amount of current flow
Do series motors have extremely low or extremely high starting to torque?
Extremely high
When a conductor cuts through magnetic lines of flux, voltage is induced in the conductor. What is this principal called?
Electromagnetic induction
What happens to the torque of DC series motor as the load is increased?
Torque increases
What happens to the speed of a DC series motor as a load increases
Speed decreases
In a compound generator, there are two different ways in which shunt windings can be connected to the armature series winding. What are they called?
Long shunt
Short shunt
What type of compound motor has its field windings wound in such a manner that they oppose each other in the production of magnetism?
Differential compound
What type of compound motor has its field windings wound in such a manner that they hate each other and production of magnetism?
Cumulative compound
What are the three characteristic voltage curves for cumulative compound generators called?
Over compounded
Flat compounded
Under compounded
How is compounding controlled in a compound dc motor or generator?
Series field rheostat
What happens to torque of a dc series motor as the load is increased?
Increases
If resistance is added to the shunt field winding circuit, what will happen to the magnetic field?
It will decrease
If resistance is removed from the shunt field winding circuit of a Dec shunt motor, what will happen to the motor speed?
It slows down
What type of devices is used for speed control of a dv shunt motor?
Shunt field rheostat
How can the speed of a dc shunt motor be controlled?
By changing the resistance of the shunt field circuit.
What is the best way to slow or stop a dc motor under normal operation?
Dynamic braking with mechanical brakes
The relationship of the Series and shunt fields in a compound generator determines the amount of _____________ for the machine.
Compounding
What type of compounding is used when constant voltage or speed is required?
Flat-compounding
How can the output voltage of a dc shunt generator be controlled?
Change the resistance of the shunt field circuit
How should the direction of rotation of a dc motor be reversed?
Interchange A1 and A2
What protective device connected in series with the shunt field do most large compound motors have?
Field loss relay
How is the windings of a interpole connected in relation to the armature?
In series
What happens to the speed of a dc series motor as the load is increased?
Speed decreases
What type of compounding occurred when a cumulative long-shunt compound motors full-load speed is greater than its no-load speed?
Over compounding
What type of compounding occurs when a differential short shunt compound generators full load voltage is less than no load voltage?
Under compounding
What is the function of the shunt field rheostat?
Voltage control for generators and speed control motors
What is the function of the series rheostat
To control the amount of compounding
A motor can be operated as a generator when the motor needs to be slowed or stopped quickly. What is this type of DC motor control called?
Dynamic breaking
Is resistance and voltage directly or inversely proportional in a DC shunt generator?
Inversely proportional
Is resistance and speed directly or inversely proportional in a DC shunt motor?
Directly proportional
What type of armature windings provide high voltage and low current?
Wave wound
What type of generator is considered a constant voltage generator?
Shunt generator or flat compounded
In a compound motor, there are two ways in which a shunt winding can be connected to the armature and series windings. What are they called?
Long shunt
Short shunt
If the current through the shunt field of a large compound motor decreases below a certain level, what protective device disconnects power to the armature?
Field loss relay
Does an increase in current flow in a conductor result in an increase of magnetic field around the conductor?
Yes
What causes the shift of the neutral plane on a DC motor under load?
Armature reaction
If resistance is added to the shunt field, winding circuit of a DC generator, what will happen to the output voltage?
It will decrease
If resistance is added to the shunt field, winding circuit of a DC generator, what will happen to the output voltage?
It will decrease
