PS Basics of an AC Motor.ppt

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POWER SYSTEMS SALES TRAINING

Purpose of an AC Motor

Electrical

EnergyMechanical

Energy

The purp ose of an AC Motor is to

Convert Electr ical Energy into Mechanical Energy

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POWER SYSTEMS SALES TRAININGTypical Motor Components

Lubrication and Pipe

Plugs

Eyebolts

Computer

Designed

Inner Bearings Caps

Shaft Run Out

Open Bearing

ConstructionModern Non-

hygroscopic

Insulation System

Integrally

Cast Frame

PositiveLubrication

System

Non-Sparking, CorrosionResistant and

Bidirectional Cooling Fans

Rotatable

Diagonally Split

Conduit Boxes

Cast Iron

E

nd Shields

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POWER SYSTEMS SALES TRAINING

AC Motor ConstructionStator

Laminations

Stator WindingAssembly

Motor Shaft

Die-cast

RotorAssembly

3 Phase Winding Circuit w/Connections T1, T2 & T3

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POWER SYSTEMS SALES TRAINING

AC MOTOR CONSTRUCTION

Stator Winding

Assembly

Rotor

Assembly

Motor Frame

Assembly

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POWER SYSTEMS SALES TRAINING

Bar Magnet

N S

Lines of Flux

Flux Density =

# of Flux Lines / per unit area

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POWER SYSTEMS SALES TRAINING

Magnetic Poles

S NS N

Unlike Poles Attract

Like Poles Repel

N SS N

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POWER SYSTEMS SALES TRAINING

Current Carrying Conductor

Lines of Flux

Conductor

Current Flow

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POWER SYSTEMS SALES TRAINING

Electromagnetic Coil

Lines of Flux

Flux Density

Dependant on:

Current

# of CoilsCore Material

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POWER SYSTEMS SALES TRAINING

Electo-magnetic Coils

Direction of Current determines Magnetic Polarity

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POWER SYSTEMS SALES TRAINING

Stator Windings

Electromagnetic Coils(Motor Windings)

Core

Stator

B2

A1

C2

B1

A2

C1

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POWER SYSTEMS SALES TRAINING

3 Phase AC PowerPhase - defines the type of electrical power

being supplied to the motorFrequency - defines how many times a second AC

changes direction: from positive to negative

Note: US Standard = 60 cycles per second (60 Hz)

Voltage - defines the amplitude of electric power

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POWER SYSTEMS SALES TRAINING

3 Phase AC Power

Each phase is displace 120

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POWER SYSTEMS SALES TRAINING

AC Motor Rotor

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POWER SYSTEMS SALES TRAINING

Synchronous Speed

F is Applied Frequency

P is Number of Poles per Phase

RPM =

120 x F

P

Synchronous Speed - The speed of the stators magneticfield rotation

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POWER SYSTEMS SALES TRAINING

AC Motor Basics

Rotating Magnetic Field of a 2 Pole AC Induction Motor

Motor RPM is equal to:

120 * Frequency

# Motor Poles

2 Pole Motor

Note that Frequency

is the only variable toaffect motor speed

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POWER SYSTEMS SALES TRAINING

Synchronous Speed

Synchronous Speed (60 Hz) = 7200

# of Poles2 pole AC mo tor = 3600 rpm

4 pole AC mo tor = 1800 rpm

6 pole AC mo tor = 1200 rpm

8 po le AC moto r = 900 rpm

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POWER SYSTEMS SALES TRAINING

Parts of an AC Motor

Electro-Magnets

Stator

Rotor

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POWER SYSTEMS SALES TRAINING

Base Speed

The Speed Produced by Applying

Motor Nameplate Rated Voltage

at

Rated Frequency

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POWER SYSTEMS SALES TRAINING

Motor Slip

N

Slip Speed = Synchronous Speed Rotor Speed

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POWER SYSTEMS SALES TRAINING

AC Motor Review

In an AC motor, speed varies by:

RPM =

120F

P - Slip

Where:

F is frequency in hertz

P is the # of motor polesSlip is in RPM

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POWER SYSTEMS SALES TRAINING

AC Motor Review

Horsepower of an AC motor can

be determined by:

HP =Torque x Speed

5252

Where:

Torque is in lb-ft

Speed is in RPM5252 is a constant

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POWER SYSTEMS SALES TRAINING

Motor Classifications

NEMA A

NEMA B

NEMA C

NEMA D

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POWER SYSTEMS SALES TRAINING

Speed / Torque Curve

0

% Torque

% Speed

Maximum orBreak-Down Torque

100

200

25 50 75 100

Synchronous

Torque

150

225Pull-Up Torque

Breakaway orStarting Torque

150% Torque

Rated Torque

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