EM Systems Intro

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Electromechanical Systems

Bilal Masood


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Contents

Introduction to Machinery Principles

Angular velocity, Acceleration

Torque, Work, Power

Magnetic Field Study

How magnetic field can affect its surroundings!

Faradays Law:

Induced Voltage from a Time-Changing Magnetic

Field Production of Induced Force on a Wire

Induced Voltage on a Conductor moving in a MagneticField


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Transformers


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Transformers

Working principle of Transformers

Construction of Transformers


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Types of Transformers

Core type Transformer

Shell type Transformer

Another means of classifying the transformeris according to the type of cooling employed

i.e;

a) Oil-filled self-cooledb) Oil-filled water-cooled

c) Air-blast type


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Machines


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AC Machinery Fundamentals


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Electric Motor

What is an Electric Motor?

Electromechanical device that convertselectrical energy to mechanical energy

Mechanical energy used to e.g. Rotate pump impeller, fan, blower

Drive compressors

Lift materials

Motors in industry: 70% of electrical load


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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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DC-Motors Components

Field pole North pole and south pole

Receive electricity to formmagnetic field

Armature Cylinder between the poles

Electromagnet when current goes through

Linked to drive shaft to drive the load

Commutator Overturns current direction in armature

(Direct Industry, 1995)


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Induction Motor


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Three-phase induction motors are the most commonand frequently encountered machines in industry

simple design, rugged, low-price, easy maintenance

wide range of power ratings: fractional horsepower to 10

MW

run essentially as constant speed from no-load to full load

Its speed depends on the frequency of the power source

not easy to have variable speed control

requires a variable-frequency power-electronic drive for optimalspeed control


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Construction

An induction motor has two main parts a stationary stator

consisting of a steel frame that supports a hollow,

cylindrical core

core, constructed from stacked laminations (why?),

having a number of evenly spaced slots, providing the

space for the stator winding

Stator of IM


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Construction

a revolving rotor

composed of punched laminations, stacked to create a series of rotorslots, providing space for the rotor winding

one of two types of rotor windings

conventional 3-phase windings made of insulated wire (wound-rotor) similar to the winding on the stator

aluminum bus bars shorted together at the ends by two aluminum rings,forming a squirrel-cage shaped circuit (squirrel-cage)

Two basic design types depending on the rotor design

squirrel-cage: conducting bars laid into slots and shorted at bothends by shorting rings.

wound-rotor: complete set of three-phase windings exactly as thestator. Usually Y-connected, the ends of the three rotor wires areconnected to 3 slip rings on the rotor shaft. In this way, the rotorcircuit is accessible.


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Construction

Squirrel cage rotor

Wound rotor

Notice the

slip rings


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Construction

Cutaway in a

typical wound-

rotor IM.Notice the

brushes and

the slip rings

Brushes

Slip rings


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Losses


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Efficiency of Electric Motors

Factors that influence efficiency

Age

Capacity

Speed

Type

Temperature

Rewinding

Load


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Synchronous Machines

Synchronous generators or alternators are used to convert

mechanical power derived from steam, gas, or hydraulic-turbine

to ac electric power

Synchronous generators are the primary source of electrical

energy we consume today

Large ac power networks rely almost exclusively on synchronous

generators

Synchronous motors are built in large units compare to inductionmotors (Induction motors are cheaper for smaller ratings) and

used for constant speed industrial drives


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Operation Principle of Generator


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Stator


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Cylindrical-Rotor Synchronous Generator

Stator

Cylindrical rotor


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Poles Stator

Rotor


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Turbine, generator and main transformer of

Kyrene Generation Station. (Courtesy Salt River Project).


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Paralleling of Generators


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Parallel operation of synchronous generators

There are several major advantages to operate generators inparallel:

Several generators can supply a bigger load than one machineby itself.

Having many generators increases the reliability of the powersystem.

It allows one or more generators to be removed for shutdownor preventive maintenance.

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Before connecting a generator in parallel with another

generator, it must be synchronized. A generator is said to be

synchronized when it meets all the following conditions:

The rms line voltages of the two generators must be

equal.

The two generators must have the samephase sequence.

Thephase angles of the two a phases must be equal.

The oncoming generator frequency is equal to the

running system frequency.

Synchronization

Load

Generator 2

Generator 1

Switch

a

b

c

a/

b/

c/

Synchronization


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Synchronization

LoadGenerato

r

Rest of the

power system

Generator

Xs1

Ef1

Xs2

Ef2

Xsn

Efn

Infinite bus

V, fare constant

Xs eq =0

G

EM Systems Intro

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