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NUE046 Alternating Current Machines

3 phase motors1 phase motors

StartersAlternators

Synchronous motors

Learning outcome 1

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This is an 80 hour module.

Divided into 3 sections

1. three phase motors and their basic theory

2. Single phase motors

3. Synchronous machines (including alternators)

ALL prac. work MUST be satisfactorily completed with a short report on each prac.

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This is an 80 hour module.

Divided into 3 sections

1. three phase motors and their basic theory

2. Single phase motors

3. Synchronous machines (including alternators)

ALL prac. work MUST be satisfactorily completed with a short report on each prac.

It is your responsibility to be an active participant in the group…… Check the forums etc.

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12 Learning outcomes

1 Principles and characteristics2 Motor Protection

3 starters4 connections to starters

5Wiring rules6 Operating principles of single phase motors

7 Parts and connections of 1 phase motors8 Comparison of 1 phase motors

9 Motor faults10 Synchronous motors

11 Loading and excitation of synchronous motors and alternators(including pracs)

12 Construction of 1 phase synchronous motors

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3 phase induction motors are common in industry.

They are rugged and reliable

Less vibration than 1 phase motors

More efficient than the same size 1 phase motor

Ref. Page 223L/O 1.1 & 1.2

Construction features

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NUE046 jh 2/05 7www.metricmind.com

Stator windings

Stator core

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www.kmmp.de/images/Web

Stator core stack

Rotor core and aluminium castings.

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The magnetic field rotates at a set speed.

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The magnetic field rotates at a set speed.

This depends on..

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The magnetic field rotates at a set speed.

This depends on.. 1. The number of poles

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The magnetic field rotates at a set speed.

This depends on.. 1. The number of poles

2. Supply frequency

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There are 3 magnetic fields in the stator each is produced by its own

AC current….

A phaseB phaseC phase

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Ref. P 228

??

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L/O 1.3 10.3.2 p 226

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The magnetic field rotates at synchronous speed

n (sync) = 120f

p

L/O 1.3 10.3.2 p 226

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The magnetic field rotates at synchronous speed

n (sync) = 120f

p

120 = 2 x 60

60 converts cycles per second to minutes.

2 because there ate north and south poles

L/O 1.3 10.3.2 p 226

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The magnetic field rotates at synchronous speed

n (sync) = 120f

p

120 = 2 x 60

60 converts cycles per second to minutes.

2 because there ate north and south poles

n is the synchronous speed

F is the frequency (Hz)

P the number of poles eg; 2, 4, 6, 8

L/O 1.3 10.3.2 p 226

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Induction The rotor gets its power from the stator by transformer action (induction).

L/O 1

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Induction The rotor gets its power from the stator by transformer action (induction).

Voltage (EMF) is induced into the rotor and hence current flows.

L/O 1

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Induction The rotor gets its power from the stator by transformer action (induction).

Voltage (EMF) is induced into the rotor and hence current flows.

This flow of current has with it a strong magnetic field.

L/O 1

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Induction The rotor gets its power from the stator by transformer action (induction).

Voltage (EMF) is induced into the rotor and hence current flows.

This flow of current has with it a strong magnetic field.

The magnetic field on the rotor reacts with the magnetic field of the stator.

L/O 1

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Induction The rotor gets its power from the stator by transformer action (induction).

Voltage (EMF) is induced into the rotor and hence current flows.

This flow of current has with it a strong magnetic field.

The magnetic field on the rotor reacts with the magnetic field of the stator.

This causes rotation.

L/O 1

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2 main types of connections

L/O 1.1 10.2.4 p 224

STATOR CONNECTIONS

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2 main types of connections

Delta connection (most common)

L/O 1.1 10.2.4 p 224

STATOR CONNECTIONS

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2 main types of connections

Delta connection (most common)Star connection

L/O 1.1 10.2.4 p 224

STATOR CONNECTIONS

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6 terminals

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EARTH CONNECTION

POSITION OF DELTA LINKS

type 1

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6 terminals

EARTH CONNECTION

POSITION OF DELTA LINKS

type 2

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STAR CONNECTION

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Terminal connections to refrig. motor

thermistors

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Compressor motor terminals

Winding arrangements

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Star and Delta

Some motors have star/delta starters.

Here the motor is first connected in star then automatically reconnected into delta as the load is applied to the motor.

In star the motor gets 230 V across the winding.

In delta it gets 415 V.

The torque is much lower in star. T α V²

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Note direction

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Main types of rotor

• Typical standard cage rotor• Wound rotor

We might see a conical type rotor in some special applications eg; cranes.

There are many different styles and designs but these are usually specialist machines.

L/O 1.1, 1.2, 1.3, 1.5

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Rotor with core stack removed.

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B.C.

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Squirrel cage rotors

standard

Bore pump

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Wound Rotor without sliprings fitted

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Conical rotor for Demag cranes and hoist motors

brakeThe rotor moves forward and releases the brake.

spring

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Wound rotor

Rotor leads

Brush gear

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Sliprings Rotor windings

Brushes and brush gearWound rotor

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Wound rotor motor nameplate

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www.visaliaelectric.com

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www.grupoensa.com

Over heated rotor.

Due to high locked rotor currents.

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Rotor frequencyAt stand still the frequency in the rotor is the same as the stator (50Hz).

At synchronous speed the rotor frequency is 0 Hz

The characteristics and performance of the motor depend on the rotor frequency due to the interaction of the 2 magnetic fields.

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Rotor frequencyAt stand still the frequency in the rotor is the same as the stator (50Hz).

At synchronous speed the rotor frequency is 0 Hz

The characteristics and performance of the motor depend on the rotor frequency due to the interaction of the 2 magnetic fields.

L/O 1.4 10.4.3 p 228

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Torque Torque is the turning effect of a motor shaft.

The torque of a motor is usually measured in newton-metres.

L/O 1.3, 1.4

1.4.1 p 5

Torque is proportional to the voltage squared.

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Torque Torque is the turning effect of a motor shaft.

The torque of a motor is usually measured in newton-metres.

L/O 1.3, 1.4

1.4.1 p 5

Torque is proportional to the voltage squared.

If you halve the voltage you get only ¼ of the torque.

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BREAKDOWN TORQUE

Torque = Turning ForceBreakdown Torque is the maximum torque

produced by the motor.This occurs then:Rotor Resistance = Rotor Reactance

RR = XLR

B.C.

p. 229 & 230

L/O 1.4

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POWEROutput power

P = ---------------2 x π x n x T

60

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POWEROutput power

P = ---------------2 x π x n x T

60

n = RPM

T = Torque

60 converts mins. to seconds

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POWEROutput power

P = ---------------2 x π x n x T

60

n = RPM

T = Torque

60 converts mins. to seconds

See example 1.6 p 5

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Losses and efficiency

All motors have losses.

We compare the input power (electrical Watts) to the output power (mechanical Watts)

Make a list of ALL losses in an electric motor.

L/O 6 1.4.2 and examples 1.7 & 1.8

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Efficiency also depends on the “quality” of the electrical supply.

η = -------P (out)

P (in)X 100

This is a percentage.

Check out the figure 10.21. P 231.

The efficiency follows closely to the power factor of the machine.

L/O 1.6

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Nameplate Data

L/O 1.5

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Nameplate DataWhat useful information do we find on the nameplate of a motor?

Voltage

Current

Watts out

Power factor

Insulation type

L/O 1.5

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Nameplate DataWhat useful information do we find on the nameplate of a motor?

Voltage

Current

Watts out

Power factor

Insulation type

WHAT ELSE ?????

L/O 1.5

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Name plate for refrig.compressor motor

Note… star/star

2 Windings are in parallel.

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