presentation of electric motor

7/30/2019 presentation of electric motor

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ELECTRIC MOTOR

An electric motor is an electromechanical

device that converts electrical energy tomechanical energy.

The mechanical energy can be used to

perform work such as rotating a pumpimpeller, fan, blower, driving a compressor,

lifting materials etc.


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BASIC WORKING PRINCIPLE


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TYPES OF MOTOR LOADS

Motorloads

Description Examples

Constanttorque loads

Output power variesbut torque is

constant

Conveyors, rotarykilns, constant-

displacement pumps

Variabletorque loads

Torque varies withsquare of operationspeed

Centrifugal pumps,fans

Constantpower loads

Torque changesinversely with speed

Machine tools


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CLASSIFICATION OF MOTORS

Electric Motors

Alternating Current (AC)Motors Direct Current (DC)Motors

Synchronous Induction

Three-PhaseSingle-Phase

Self ExcitedSeparatelyExcited

Series ShuntCompound


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TYPES OF AC MOTORS

* Electrical current reverses direction

* Two parts: stator and rotor

Stator: stationary electrical component

Rotor: rotates the motor shaft

* Speed difficult to control

* Two types

Synchronous motor Induction motor


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AC MOTOR: INDUCTION MOTOR

Most common motors in industry

Advantages:

Simple design

Inexpensive

High power to weight ratio Easy to maintain

Direct connection to AC power source


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COMPONENTS OF INDUCTIONMOTOR

A3-phase induction motor has two main parts:

A stator consisting of a steel frame that supports ahollow, cylindrical core of stacked laminations. Slots onthe internal circumference of the stator house the stator

winding. A rotor also composed of punched laminations, withrotor slots for the rotor winding.


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COMPONENTS OF INDUCTIONMOTOR contd

There are two-types of rotor windings:

Squirrel-cage windings, which produce asquirrel-cage induction motor(most common)

Conventional 3-phase windings made of

insulated wire, which produce a wound-rotorinduction motor(special characteristics)


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Induction Motor: OperatingPrinciple

Operation of 3-phase induction motors is based upon theapplication of Faradays Law and the Lorentz Force on aconductor.

Consider a series of conductors (length L) whose

extremities are shorted by bars A and B. A permanentmagnet moves at a speed v, so that its magnetic fieldsweeps across the conductors.


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Operating Principle Contd

The following sequence of events takes place:

1. A voltage E = BLv is induced in each conductor while itis being cut by the flux (Faradays Law)

2. The induced voltage produces currents which circulate

in a loop around the conductors (through the bars).3. Since the current-carrying conductors lie in a magnetic

field, they experience a mechanical force (Lorentzforce).

4. The force always acts in a direction to drag the

conductor along with the magnetic field. Now close the ladder upon itself to form a squirrel

cage, and place it in a rotating magnetic field aninduction motor is formed!


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Induction Motor: Rotating Field

Consider a simple stator with 6 salient poles -windings AN, BN, CN.

The windings are mechanically spaced at 120 fromeach other.

The windings are connected to a 3-phase source. AC currents Ia, Ib and Ic will flow in the windings, but

will be displaced in time by 120.

Each winding produces its own MMF,which creates aflux across the hollow interior of the stator.

The 3 fluxes combine to produce a magnetic field thatrotates at the same frequency as the supply.


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Induction Motor: Stator Winding

In practice, induction motors have internal diametersthat are smooth, instead of having salient poles.

In this case, each pole covers 180 of the innercircumference of the rotor (pole pitch = 180).

Also, instead of a single coil per pole, many coils arelodged in adjacent slots.

The staggered coils are connected in series to form aphase group.

Spreading the coil in this manner creates a sinusoidalflux distribution per pole, which improvesperformance and makes the motor less noisy.


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INDUCTION MOTOR : SLIP

The difference between the synchronous speed androtor speed can be expressed as a percentage ofsynchronous speed, known as the slip.

s = (Ns N)Ns

Where s = slip, Ns = synchronous speed (rpm), N = rotorspeed (rpm)

At no-load, the slip is nearly zero (


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Induction Motor: Frequencyinduced in the rotor

The frequency induced in the rotor dependson the slip:

fR= s f

fR= frequency of voltage and current in the

rotorf = frequency of the supply and stator field

s = slip


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Induction Motor: Active Power Flow

Efficiency by definition, is the ratio of output

/ input power: = PL / Pe Rotor copper losses: PJr = s Pr

Mechanical power: Pm = ( 1-s)Pr Motor torque: Tm = 30Pr

Ns

Where: Pe = active power to statorPr = active power supplied to rotor

PL = Shaft Power


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Power Losses

I d ti M t R l ti hi


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Induction Motor: Relationshipbetween Load, Speedand Torque

At full speed: torqueand stator currentare zero

At start: highcurrent and lowpull-up torque

At start: highcurrent andlow pull-uptorque

At 80% of fullspeed:highest pull-

out torqueand currentdrops


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PRESENTED BY:-

SOURABH RANJAN

VYOM DIXIT VIVEK KUMAR JHA

MANISH JADAUN


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THE END

presentation of electric motor

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