Handouts 1,2,3,5 Flashcards by justin Manaigre

What happens to the speed of an AC universal motor as the load is decreased ?

Load goes down then the speed goes up

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What is the primary difference between a start-type and run-type capacitor?

start electrolytic

- run oil filled

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When creating a magnetic field, do the lines of flux flow from south to north across the air gap?

No, North to south

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What is the rotational force produced by a motor called?

Torque

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What type of AC machine coverts electrical input to mechanical output?

Motor

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In an AC universal motor, are torque and speed directly or inversely proportional to each other?

Inversely

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What approximately percentage of rated speed does a centrifugal switch open at?

75%

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If the centrifugal switch fails to open as a capacitor-start induction-run motor accelerates to its rated speed, what could happen to the starting windings?

Overloads trip/ windings over heat

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In reference to the left hand rule for conductors, what do the fingers and thumb represent?

Thumb- electron flow

Fingers- magnetic lines

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In reference to the left hand rule for electromagnets, what do the fingers and thumb represent?

Thumb- north end

Fingers- electron flow

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What is a measure of a materials ability to become magnetized called?

Permeability

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What component of an AC machine supports the shaft and allows it to rotate freely?

Bearings

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Does the stator of an AC machine produce a stationary magnetic field or an alternating magnetic field?

Alternating magnetic field

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What are the terminal markings for start windings leads?

T5 and T8

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In a capacitance start induction run split phase induction motor start field windings are wounded with ________ turns of __________ gauge wire relative to the run field windings

More, smaller

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To reverse a 4 lead permanent slip capacitor motor, which wiring connections are interchanged?

T5 T8

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List three types of power losses that occur in a split phase induction motor

Eddy currents
Hysteresis
Heat

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Does the counter emf generated increase or decrease as the load is added to an ac series universal motor

CEMF goes up
LOAD goes up
(Increases) is the answer

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What type of single phase AC motor has the highest starting torque characteristics?

Universal series motor

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A rotating magnetic field is produced in an AC motor by “splitting” the phase through two separate field windings. What type of motor uses this principle?

Split phase induction motor

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Why are pole pieces constructed of laminated sheets

To reduced eddy currents or to minimize losses

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What are the brushes in an AC universal motor made of?

Carbon graphite

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What is the minimum number of terminal leads require for connection of a dual voltage 115/230v resistance start induction run motor?

6 leads

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In an AC universal motor when proper commutation is taking place, what colour is the commutator?

Dark chocolate

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In a permanent magnet motor, where are magnetic flux lines most densely concentrated?

At the poles

What types of capacitor does a permanent split capacitor motor use?

Oil filled capacitor

What type of capacitor does a capacitor start induction run motor use?

Electrolytic

What are two factors that determine the amount of torque developed by a motor load?

Strength of magnetic field | Current

What is the portion of the stator pole piece is closest to the rotor assembly called?

Pole shoe

How is the capacitor in a capacitor start induction run split phase motor connected?

In series with the start windings

What solid state device can be used to disconnect the start windings in a resistance start induction run split phase motor

Thermistor

Does a current relay use normally open or normally closed contact is connected in series with the start windings?

Normally open

What type of motor has a short circuited time of heavy copper wire wounded around part of the stator pole?

Shaded pole induction motor

When an AC motor is first started, why is the inrush current so high?

Low CEMF

What are two advantages of a resistance start induction run motor

Good for frequent start condition | Constant fixed speed

What are two disadvantages of a resistance start induction run motor?

High starting surge current | Limited to 1/3 HP

What are two advantages of a capacitor start induction run motor?

Low in rush current on start up | High starting torque

What are two disadvantages of a capacitor start induction run motor

Can’t be started more than 8 times per hour | Prolonged current flow will damage capacitor

What are two advantages of a permanent split capacitor motor

Good starting torque | Good running torque

What are two disadvantages of a permanent split capacitor motor

Cap can over heat | Relies on cap

What are two advantages of a capacitor start capacitor run motor

Constant fixed speed | Good running torque

List five methods used in split phase motors to disconnect the start windings

``` Centrifugal switch Hot wire windings Current relays Potential relays Solid state starting relay ```

In a resistance start induction run split phase induction motor run field windings are winded with __________ turns of ___________ gauge wire relative to the start field windings

Less, larger

To reverse a 6 lead split phase induction motor which wiring connection are interchanged

T5 and T8

Is the starting torque characteristics of a capacitor start motor greater than or less than the starting torque characteristics of a resistance start motor

Greater

Which type of disconnecting means for a split phase motor functions as both a starting relay and an overload relay

Hot wire relay

Which split phase motor have their start windings disconnected after initial rotation is developed durn start up?

Resistance start induction run | Capacitor start induction run

Which split phase motors have their start windings energized at all times

Permanent split capacitor | Capacitor start capacitor run

What is the maximum phase displacement angle between the start and run windings of a capacitor start induction run split phase motor

90°

What is the function of a centrifugal switch

Mounted inside a motor that serves as a disconnect the start windings

What type of single phase motor would be best suited to be used for a residential refrigerator

Capacitor start induction run

What is a thermistor

Device that exhibits a change of resistance with change of temperature

Is the resistance of a start field windings higher or lower than the resistance of the run field windings in a capacitor start induction run split phase induction motor

Higher

What are the minimum number of stator leads required for a single voltage, reversible split phase induction motor

What are the minimum number of stator leads required for a dual voltage reversible split phase induction motor

What are the minimum number of stator leads required for a single voltage non reversible split phase induction motor

List three application of permanent split capacitor motors

Central air conditioners Air handlers Blowers

List three applications of resistance start induction run motors

Washer machine Dishwasher Clothes dryer

List three applications of capacitor start induction run motors

Fridges Freezer Wine cooler

List two types of capacitors used in split phase induction motors

Oiled filled | Electrolytic capacitors

When an AC motor is first started why is the in rush current so high?

The rotor current is only limited by the very low rotor circuit resistance

What type of single phase motor does not use a squirrel cage rotor assembly

Universal series motor

List two factors that determine the amount of torque developed by a motor

Strength of the main magnetic fields | Amount of current flow

Why are pole pieces laminated

To minimizes the circulation of induced eddy currents within the core and hysteresis

What type of single phase motor is typically not reversible

Shaded pole induction motor

In an AC universal motor are torque and speed directly or inversely proportional to each other

RPM goes down Torque goes up So torque and speed are inversely

If the number of poles in a shaded motor is double does the speed of the motor increase or decrease

Decreases

What is the typical phase displacement angle in a shaded pole motor

10°

What happens to the torque of an AC universal motor if the load is increased

If the load increases the torque will increase as well

The amount of CEMF produced in a rotor assembly is proportional to what three factors

Amount of conductors The magnetic field strength The speed of rotation

Is the shaded pole an induction motor

Yes

Why are pole pieces constructed with silicon steel

To reduced hysteresis

In universal motors, are the armature and field coils connected in series or parallel?

Series

Which single phase motor is considered to be the most simple and least expensive?

Shaded pole induction motor

What is the formula for synchronous speed

RPM=120xhz/# of poles

What is the formula for rotor speed

RPM=120xhz/# of poles -%slip

How should the direction of rotation of an AC universal motor be revered

Interchange armature leads A1 and A2

Does a shaded pole induction motor rotate in the direction towards the shading coil potion of each pole piece or away from the shading coil portion of each pole Piece

Towards

Does the CEMF generated increase or decrease as load is added to an AC series universal motor

Load goes up CEMF goes up It increases

List three applications of shaded pole motors

Small fans Timers Clocks

List three applications of AC universal motor

Power tools Sump pumps Razors

List three types of power losses that occur in AC machines

Mechanical Electrical Magnetic

When creating a magnetic field, do the lines of flux flow from the north to the south across the air gap?

Yes

What are the three factors that determine the strength of an electromagnet

Conductors Current Core

Where are magnetic flux lines most densely concentrated

At the poles

What is measure of a material ability to become magnetized called

Permeability

What is resistance to magnetism called

Reluctance

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 magnétisant force has stopped called

Residual magnetism

In reference to the left hand rule for conductors, what do the fingers and thumbs represent

Thumb- current | Fingers- field

In reference to the left hand rule for electromagnets what do the fingers and thumb represent

Thumb- north field | Finger- current

Does an increase in current flow in a conductor result in an increase of magnetic field around the conductor

Yes

What are two types of magnets

Permanent magnets | Electromagnets

What is the rotational force produced by a motor called

Lorentz force

When a conductor cuts through magnetic lines of flux a voltage is induced into the conductor. What is this principle called?

Electro magnetic induction

In reference to the right hand rule motors what do the thumb, forefinger and middle finger represent

Thumb- thrust Forefinger- field Middle finger- current

Does the stator of an AC motor produce a stationary magnetic field or a rotating magnetic field

Rotating magnetic field

What is the purpose of a field winding in an AC machine

Create magnetic lines of flux

Is a field winding in an AC motor considered an electrical load or an electrical source

Electrical load

What are two types of bearings found in an AC machine

Sleeve and rolling

Provide two reasons why the poles shoe of every pole piece is curved to conform to the surface of the rotor assembly

Wider and more even flux distribution

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

Shaft Iron core Rotor windings

What components of an ac machine supports the shaft and allows it to rotate freely

Bearings

List with electrical input requirements that are found on an AC machine name plate

``` Manufacture name Model number Serial number Rated voltage Current (FLA) kilowatts Horsepower Speed ```

How are eddy currents minimized in an AC machine

Thin coat of enamel within the core

How are hysteresis minimized in an AC machine

Silicone steel alloys

What components 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

Air gap Pole shoes Shaft Frame

List 4 components of the electric circuit in an AC machine

Brushes Field windings Lead Series field windings

List 4 mechanical components used in an AC machine

Frame End plates Bearings Base

What are the four types of enclosures for AC machines

Open type Weather proof Drip proof Totally enclosed type