Assignment 1
When creating a magnetic field, do the lines of flux flow from north to south across the air gap?
Flux lines are directional. They exit the north and enter the South Pole
Where are magnetic flux lines most densely concentrated?
Magnetic flux lines are most densely concentrated at the poles
What are the three factors that determine the strength of an electromagnet?
1. The amount of conductors (no. of turns, length and size of conductor)
2. The magnetic strength of the core material
3. The amount of current flow
What is a measure of a material’s ability to become magnetized called?
Permeability- (a measurement of a material’s ability to conduct magnetic lines of flux)
What is resistance to magnetism called?
Reluctance - (resistance to magnetism)
When an electromagnet reaches a point where strength increases only slightly with an increase in
current, it is known as a point of _____________.
Saturation
What is the amount of magnetism left in a material after magnetizing force has stopped called?
Residual magnetism
In reference to the left-hand rule for conductors, what do the fingers and thumb represent?
Thumb – Direction of current flow
Fingers – Direction of the magnetic field around the conductor
In reference to the left-hand rule for electromagnets, what do the fingers and thumb represent?
Thumb – Points to the direction of the north pole
Fingers – Direction of current flow
Does an increase in current flow in a conductor result in an increase of magnetic field around the conductor?
As the current increases in a conductor the magnetic field will increase proportionally
What are two types of magnets?
1. Permanent - No external force to maintain their magnetic properties
2. Electromagnets - relies on electricity to become magnetized
What is the rotational force produced by a motor called?
The turning force developed by a motor is torque
When a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor. What is this principle called?
Electromagnetic Induction, whenever a conductor cuts through magnetic lines of flux a voltage is induced into the conductor. (reverse from electromagnetic flow through a conductor)
When a conductor cuts through magnetic lines of flux, a voltage is induced into the conductor. What is this principle called?
Electromagnetic Induction, whenever a conductor cuts through magnetic lines of flux a voltage is induced into the conductor. (reverse from electromagnetic flow through a conductor)
In reference to the right-hand rule for motors, what do the thumb, forefinger & middle finger
represent?
Thumb –Direction of the Lorentz Force on the conductor
Forefinger –Orientation of magnetic field produced by the field windings
Middle finger –Current in the armature conductor
Does the stator of an AC motor produce a stationary magnetic field or a rotating magnetic field?
The field it produces is a rotating magnetic field
What is the purpose of a field winding in an AC machine?
The role of the field windings is to create magnetic flux
Is a field winding in an AC motor considered an electrical load or an electrical source?
Motor - electrical load
(Alternator - source)
What are two types of bearings found in AC machines?
Sleeve bearings
Ball Bearings
Provide two reasons why the pole shoe of every pole piece is curved to conform to the surface of
the rotor assembly?
Results in wider and more even flux distribution
Minimize the air gap between the rotor and stator
What is the portion of the pole piece closest to the rotor called?
Pole Shoe
What are the three components that comprise a rotor assembly?
1. Shaft (Steel cylinder that forms the axis for rotation of the rotor assembly)
2. Iron Core (An iron cylinder that has slots cut into it)
3. Rotor Windings (Consists of bare or insulated conductors wound into the slots of the iron core)
What component of an AC machine supports the shaft and allows it to rotate freely?
Bearings
List eight electrical input requirements that are found on an AC machine nameplate.
1. Voltage
2. Current
3. Frequency
4. Phase
5. Code (a letter from a to v is used to indicate the locked rotor KVA per horsepower. This indicates
the amount of inrush current per hp at motor start up)
6. Power factor
7. Effiency
8. kW or hp
How are eddy currents minimized in an AC machine?
Laminations insulated from each other by a thin coating of enamel
How is hysteresis minimized in an AC machine?
Hysteresis minimized by use of silicon-steel alloys for the construction of the rotating machine
What component forms the axis for rotation of the rotor assembly in an AC machine?
Shaft
List 4 components of the magnetic circuit in an AC machine.
1. Rotor assembly
2. Pole piece
3. Field windings
4. Frame
List 4 components of the electric circuit in an AC machine.
1. Field windings
2. Terminal leads
3. Centrifugal switch
4. Commutator and brushes
List 4 mechanical components used in an AC machine.
1. Centrifugal switch
2. Bearings
3. Shaft
4. Fan
What are the four types of enclosures for AC machines?
1. Open-type
2. Weatherproof
3. Drip-proof
4. Totally enclosed type
Resistance-start induction-run single-phase motor components
1. Terminal leads
2. Shaft
3. ball bearing
4. End plate or end bell
5. Field windings
6. Pole piece
7. Housing or frame
8. Rotor
9. Cooling fan
10. Base