Induction Motor Presentation

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INDUCTION MOTOR


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What is Induction Motor?


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PARTS AND ITS FUNCTION


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The Stator and the Rotor are each made up of:

An electric circuit(insulated copper or aluminum)

A magnetic circuit

(laminated steel)


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STATOR

Stationary electrical part of the motor Made up of several thin laminations of aluminum

or cast iron

Sometimes referred to as the windings

Consists of poles carrying supply current to

induce a magnetic field that penetrates the rotor


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The Stator

The stator is the outer stationary part ofthe motor

The Stator is consists of:

The ou ter cyl ind r ical frame of the moto r

The magnet ic path

A set of insu lated electr ical w ind ings


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The Stator


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Stator coil

The stator coils are the copper wiresembedded into the stator of the induction

motor.

The current flows into these wires toproduce a magnetic field making the rotor

of the motor rotate in one direction.

The direction of the mmf depends uponthe instantaneous current flows and using

the right hand rule.


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Three phase motor

The three phase induction motors are themotors mostly frequently encountered in

industry.

They run at essentially constant speedfrom zero to full-load.

The speed is frequency-dependent and,

consequently, these motors are not easilyadapted to speed control.


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The only way to solve theproblem of the singlephase is to build a 2-phase motor, derivingpower from single phase.

This requires a motor withtwo windings spacedapart 90 electrical, fedwith two phases ofcurrent displaced 90 in

time. This is called a

permanent-split capacitormotor.


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ROTOR

Rotating part of theelectromagnetic circuit

Most common type of rotor is

the squirrel cage

Consist of a group ofelectromagnets arranged

around a cylinder with a poles

facing towards the stator

poles

Located inside the stator


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The AC Induction Motor comprises 2

Electromagnetic Parts

Stationary part called the stator Rotating part called the rotor


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The Rotor

The Rotor is the rotating part of the motor constructed of copper or aluminum strips

consists of a set of slotted steel

laminations The electrical circuit of the rotor can be

either:

Wound rotor type

Squirrel cage roto r type


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The Rotor


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BEARING

Hold the rotating shaft to the motor frame support the rotor and allow it to turn

Common bearings are the sleeve type and

the ball type

Lubricated with oil

Bearing


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Bearing

the purpose of bearing is they avoid thedirect contact between the outer and innersurface and thus reducing the friction andthe given power can be used economical

The shaft is mounted onthe bearing so it canrotate freely.

Ball Bearing


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Bearing Lubrication

Reduce friction

Reduce Transfer heat

Carry away contaminants

and debris

Protect against wear Prevent corrosion


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FRAME

Holds all the parts in place

Provides a means of mounting

the motor to machinery

Conducts heat produced within

the motor to the surrounding air Protects the electrical and

operating parts of the motor

from harmful effects of the

environment in which the motoroperates


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FORMULAS


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Other Parts


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ADVANTAGES AND DISADVANTAGES

Advantages Simple and rugged in construction

Cheaper in cost due to the absence

of brushes, commutators, and slip

rings

They are maintenance free motors

unlike dc motors and synchronousmotors due to absence of brushes,

commutators and slip rings

Can be operated in polluted and

explosive environments as they do

not have brushes which can cause

sparks 3 phase induction motors will have

self starting torque, hence no

starting methods are employed

unlike synchronous motor

Disadvantages 3 phase induction motors have poor

starting torque and high in rush

current

They always operate under lagging

power factor and during light load

conditions they operate at veryworst power factor.

Hence capacitor banks should be

placed to deliver the reactive power

Speed control of induction motors

are difficult, hence for fine speed

control applications dc motors areused. Due to advance in power

electronics, variable frequency

drives using induction motors are

used in industries for speed control


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AC electric induction motors(Efficiencies)


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Definition of energy efficiency

Efficiency is the ratio of mechanical energyoutput divided by the electrical energy

input. There are different efficiency

definitions

that describe the relationship between a

motors rating and

efficiency test results


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Electrical Motor Efficiency when ShaftOutput is measured in Watt

If power output is measured in Watt(W), efficiency can be expressed as:

m=Pout/ PinWhere:

m= motorefficiency

Pout= shaft power out (Watt, W)Pin= electric power in to the motor (Watt,

W)


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Electrical Motor Efficiency when ShaftOutput is measured in Horsepower

If power output is measuredin horsepower (hp), efficiency can be

expressed as:m=Pout746 / Pin

Where:

Pout= shaft power out (horsepower, hp)Pin= electric power in to the motor (Watt,W)


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Minimum Nominal Efficiencies

Power

(hp) Minimum Nominal Efficiency1)

1 - 4 78.8

5 - 9 84.0

10 - 19

85.5

20 - 49 88.5

50 - 99 90.2


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1 - 4 78.8

5 - 9 84.0

10 - 19 85.5

20 - 49 88.5

50 - 99 90.2

100 - 124 91.7

> 125 92.4


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Several more innovative approaches toimproving efficiency are currently being

attempted in the industry. For induction

motors, the most notable change is the

move from cast aluminum rotors to cast

copper rotors. This can raise efficiency by

about 1% at three horsepower (3 hp).

However, the cost of cast copper rotors isa significant factor.


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Aluminum Vs Copper

Lower coefficient of expansion for copper:aluminium will creep and move approximately33% more than copper.

Higher tensile strength for copper: copper is

300% stronger than aluminium and thus ableto withstand high centrifugal force and therepeated hammering from currentinducedforces during each start.

Higher melting point of copper: copper canbetter withstand thermal cycling over the lifeof the motor.

Losses that may affect the


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Losses that may affect the

efficiency of an induction motor Primary and Secondary Resistance Losses

The electrical power lost in the primary rotorand secondary stator winding resistance are alsocalled copper losses. The copper loss varies withthe load in proportion to the current squared - and

can be expressed as

Pcl= R I2

Where:

Pcl= stator winding - copper loss (W)R= resistance ()

I = current (Amp)


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Iron LossesThese losses are the result of magnetic energy

dissipated when when the motors magnetic field

is applied to the stator core.


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Stray Losses

Stray losses are the losses that remains afterprimary copper and secondary losses, iron

losses and mechanical losses. The largestcontribution to the stray losses is harmonicenergies generated when the motor operatesunder load. These energies are dissipated as

currents in the copper windings, harmonic fluxcomponents in the iron parts, leakage in thelaminate core.


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Mechanical LossesMechanical losses includes friction in the motor

bearings and the fan for air cooling.


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ENDppt made by:

Capuno, Charles Brian C.

Induction Motor Presentation

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