Fund Course Module 7

8/14/2019 Fund Course Module 7

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Module 7

Fundamentals ofPower Plant

Electricity


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Learning Objectives

Fundamentals of basic electricity

The relationship of voltage,

current, and resistance

How voltage is produced

How alternating current electricityworks


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Basic Power Plant

Electricity Electricity is a

phenomenonassociated with

stationary or movingelectric charges and isone of the basic formsof energy.

Electrical activity

takes place constantlyeverywhere in theuniverse.


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Electrons and Electrical

Charge To understand

electricity, one

must first take alook at atoms.

Atoms are thebuilding blocks

that make up allforms of matter.

Atom with Electron in Orbit


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Charge A typical atom

has a nucleus in

its center. The nucleus is

composed of twodifferent types of

tiny particles:protons andneutrons.



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Charge Other tiny

particles, called

electrons, orbitaround thenucleus.



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Charge All atoms have the same basic

structure.Yet the number of protons, neutrons,

and electrons in an atom varies fromone material to another.


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Charge Of the three

types of particles

in atoms, onlytwo of them,protons andelectrons, are

important in thestudy ofelectricity.



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Charge Protons and electrons are "charged"

particles, which means that they react

electrically.


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Charge Neutrons are not charged, so they are

not considered when looking at the

electrical characteristics of an atom


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Electric Charge

Electrons and protons both carry exactly thesame amount of electric charge.

The positive charge of the proton is exactlyopposite the negative charge of the electron.

If an object has more protons than electrons, itis positively charged; if it has more electronsthan protons, it is negatively charged; and if itcontains as many protons as electrons, the

charges cancel each other and the object iselectrically neutral.


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Electric Charge

To show that protons andelectrons have opposite charges,

but that the values of the chargesare equal, it usually said that eachproton has a charge of +1 and

each electron has a charge of 1.


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Electric Charge

There are three importantfacts to remember aboutelectrical charges: Opposite electrical charges

of equal value cancel eachother out.

Opposite electrical chargesare attracted by eachother.

Like electrical charges arerepelled by each other.


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Electric Charge

The charges on a proton and anelectron cancel each other out,

because a +1 charge and a -1charge are opposite charges ofequal value.


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Coulombs Law

Coulombs Law states that objectswith opposite charges attract each

other, and objects with similarcharges repel each other.


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Coulombs Law

The greater the charges on the objects,the larger the force between them; the

greater the distance between theobjects, the lesser the force betweenthem.

The unit of electric charge, also named

after Coulomb, is equal to the combinedcharges of 6.24 1018 protons (orelectrons).


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Charging by Induction

A charged object may induce a chargein a nearby neutral object withouttouching it.

For example, if a positively chargedobject is brought near a neutral object,the electrons in the neutral object areattracted to the positive object.

Some of these electrons flow to theside of the neutral object that isnearest to the positive object.


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This side of the neutral objectaccumulates electrons and

becomes negatively charged. Because electrons leave the far

side of the neutral object while its

protons remain stationary, thatside becomes positively charged.


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The net effect is an attractionbetween the objects.

Similarly, when a negativelycharged object is brought near aneutral object, the negative object

induces a positive charge on thenear side of the neutral object anda negative charge on the far side.


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The induced charges are notpermanent.

As soon as the charged object istaken away, the electrons on theother object redistribute

themselves evenly over it, so thatit again becomes neutral.


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Electric Current

The interaction between positivelycharged protons and negatively

charged electrons is what electricity isall about.


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Electric Current

If a potential difference is establishedbetween two points, and some chargesare released, then these charges will be

acted on by the electrical force and startto move.

The movement, or flow, of electrons iselectric current.


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Electric Current

Electric current can flow as long astwo requirements are met:

There must be a complete paththrough which the electrons can flow(Electrical Circuit).

There must be a force to push theelectrons along (Voltage).


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Sources of Electric Current

There are severaldifferent devicesthat can supply the

voltage necessaryto generate anelectric current.

The two mostcommon sources

are generators andelectrolytic cells(battery). Battery


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Generatorsproduce electricity

via magnetism.

Electrolytic cellsuse chemical

energy to produceelectricity.

Magnetism


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Other sources of electric current are:

Thermoelectricity Photoelectricity

Piezoelectricity


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Thermoelectricity

Thermoelectricity is electricity

produced byheating twometals.

Electricity Produced by Heat


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Photoelectricity

Photoelectricity is electricity

produced in asubstance bylightening.

Photoelectricity


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Piezoelectricity

Piezoelectricityis electricity

produced bycertain crystalswhen pressure isapplied.

Electricity Produced by

Compressing Quartz


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Measurement of Electric

Current Electric current is measured in

units called amperes (amp).

If 1 coulomb of charge flows pasteach point of a wire every second,the wire is carrying a current of 1amp.

If 2 coulombs flow past each pointin a second, the current is 2 amp.


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Measurement of Electric

Current

A coulomb is a unit of quantity used to

measure electrical charges. One coulomb is equal to the amount of

charge transported by a current of oneampere in one second.


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Electrical Circuits

The path through which electrons canflow is called an electrical circuit.

An electric circuit is an arrangement ofelectric current sources and conductingpaths through which a current cancontinuously flow.


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Simple Circuit

A very simple circuitmade up of abattery and a length

of wire. One terminal of the

battery is positivelycharged and the

other terminal isnegatively charged.

Simple Circuit


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Simple Circuit

Current will flowthrough this circuitas long as there isa "potentialdifference"between thepositive andnegative charges.

Simple Circuit


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Simple Circuit

The term "potentialdifference" meansthat the positive

and negativecharges are notequal; if they wereequal, they would

cancel each otherout and currentcould not flow. Simple Circuit


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Simple Circuit

The potential difference betweenpositive and negative charges is

voltage, which is the force thatpushes electrons along.

So current only flows when

voltage is present.


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Simple Circuit

The wire in thepicture connects

the negativeterminal of thebattery to thepositive terminal.

It provides a paththrough whichcurrent can flow.

Simple Circuit


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Simple Circuit

The wires inelectrical circuitsare often made of

copper, becausecopper is a materialthat allows currentto flow easily.

Such materials arecalled conductors.

Conductor


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Simple Circuit

Silver and aluminum are also goodconductors.

Like copper, they offer littleresistance to the flow of electrons.


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Simple Circuit

Other materials,such as rubberand string, for

example, offer agreat deal ofresistance to theflow of electrons.

These materialsare calledinsulators. Insulators


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Simple Circuit

The circuit in thepicture is a

complete circuit,an uninterruptedpath for currentflow.

Simple Circuit


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Simple Circuit

If one end of thewire isdisconnected

from its terminal,the circuit is nolonger complete:current can't

flow, because itspath has beeninterrupted. Incomplete Circuit


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Simple Circuit

An interruptedcurrent path is

called an opencircuit, or just anopen.

Open Circuit


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Simple Circuit with Load

A part of an electric circuit other thanthe source of electric current is called a

load. The load includes all components

placed in the circuit, such as lights,connecting wires, switches, fuses, and

other devices. A load is any device that performs a

function when current flows through it.


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An example of anelectrical circuitwith load is shown

in the picture. The main

components in thecircuit are a

battery, a lightbulb, and a switch.Electric Circuit with Load


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The battery inthe circuit is the

voltage source. The voltage

produced by thebattery pushes

current throughthe circuit.

Circuit with Load


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The light bulb in thiscircuit is referred toas a load, because a

load is any devicethat performs afunction whencurrent flowsthrough it.

The function thatthe light bulbprovides is, ofcourse, to light up.

Circuit with Load


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Any device that is used as a load in anelectrical circuit opposes the flow ofcurrent through the circuit.

Therefore, a load is the opposition tocurrent in a circuit.

Opposition to current is just anotherway of saying resistance.

All electrical circuits have someresistance in them.


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Conductors and Insulators

Some materials,called conductors,allow an electric

current to flowthrough them easily.

Other materials,called insulators,

strongly resist thepassage of anelectric current.

Insulators


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Since conductors are materials that allowan electric current to flow through themeasily, most metals are good conductors.

At commonly encountered temperatures,silver is the best conductor and copper isthe second best.

Electric wires are usually made of copper,

which is less expensive than silver.


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Since insulators do not allow electric currentto flow through them, another name forthem is nonconductors or dielectrics.

Rubber, glass, and air are commoninsulators.

A conductor allows an electric current toflow through it, but it does not permit thecurrent to flow with perfect freedom.


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Conductance and

Resistance Collisions between the electrons and the

atoms of a conductor can interfere withthe flow of electrons.

This phenomenon is known asresistance.

Resistance is measured in units called

ohms. The symbol for ohms is the Greek letter

omega, .


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Conductance and

Resistance Since resistance is the opposition

to current flow, then conductance

is the ability of a material to allowcurrent flow.

So a good conductor is one thathas low resistance.

A good insulator has a very highresistance.


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Short Circuits

A short circuit occurs when theresistance in a circuit, or part of acircuit, drops to almost zero.

Short Circuit


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Voltage

The force that pushes electronsalong is what is called voltage.

Another name for a voltageproduced by a source of electriccurrent is electromotive force.


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Voltage

There are six ways that voltage canbe produced:

Light Pressure

Heat

Friction

Chemical action

Magnetism


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Light

Photoelectriccells use light toproduce voltage.


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Light

The alloy loseselectrons, so itbecomes

positivelycharged.

The iron gainselectrons, so it

becomesnegativelycharged.


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Light

The differencebetween thepositive and

negative chargesis voltage.

The more intensethe light, the

greater thevoltageproduced.


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Light

Photoelectric cells areoften used to producevoltage in remotestations that have no

power lines going tothem.

The voltage that'sproduced when light isavailable can be stored in

batteries and then usedto supply power at nightor on cloudy days.


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Pressure

Pressure can beapplied to certaintypes of crystalsto producevoltage.

Electricity Produced by Compressing


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Pressure

When the right sortof crystal is putbetween metal

plates and thensubjected topressure, electronsare driven out of the

crystal and onto oneof the metal plates.



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Pressure

The plate thatreceives theelectrons becomes

negatively charged. The potentialdifference betweenthe negativelycharged plate and

the other plate isthe amount ofvoltage produced. Electricity Produced by Compressing


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Pressure

When the negativelycharged plate has anegative charge of 1

volt, and the otherplate has no charge,the voltageproduced is 1 volt: 0

volts (1 volt) = 1volt.



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Heat

A thermocouple is a good example ofusing heat to produce voltage.

a thermocouple is made of two different

metals joined together. When heat is applied at the point where

the two metals join, the two metalsrespond differently.

Thermocouple


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Heat In one of the metals, electrons move

toward the junction where heat isapplied.

In the other metal, electrons moveaway from that junction.

The amount of voltage produceddepends on the difference in

temperature between the point whereheat is applied (the hot junction) andthe opposite ends of the metals (thecold junction).


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Friction

The kind ofvoltage thatfriction produces

is generally moreof a nuisancethan a usefultype of voltage.

Friction is therubbing togetherof two materials.


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Friction

Voltage producedby friction isreferred to asstatic electricity.

In most cases, itis eliminated

rather than used.


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Chemical Action

Batteries use chemical action toproduce voltage.

Batteries come in a variety of shapesand sizes, and they perform a widerange of functions, from keeping aflashlight operating to providing

emergency power for a power plantwhen the main power system goesdown.


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Chemical Action

All batteries aremade up of cells,even though thenumber of cellsvaries from onetype of battery to

another.


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Chemical Action

A flashlightbattery has onlyone cell, forinstance, while aplant batterymight have 60

cells or more.Plant Battery


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Chemical Action

A cell usuallyconsists of twoplates ofdifferentmaterialssurrounded by a

liquid or pastecalled anelectrolyte.


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Chemical Action

The chemicalaction thatproduces voltagein a battery is areaction betweenthe plates and

the electrolyte.


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Chemical Action

There are twobasic types ofcells: primarycells andsecondary cells.

Secondary Cell


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Chemical Action

There are two major differencesbetween primary cells and

secondary cells: Most primary cells use a moist paste

for an electrolyte, while secondarycells have liquid electrolytes; and

Primary cells can't be recharged, butsecondary cells can.


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Chemical Action

In the cell of a typical flashlight battery,one of the plates is made of zinc andthe other one is made of carbon.

The electrolyte is a paste made ofstarch, flour, and other ingredients.Because the electrolyte is relatively

dry, this type of battery is often calleda dry cell.


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Chemical Action

As a result of chemical action betweenthe plates and the electrolyte, anegative charge builds up on the zincplate and a positive charge builds upon the carbon plate.

While this is happening, the zinc plate

slowly dissolves. When the zinc plate iscompletely dissolved, the cell is dead,so it is replaced.


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Chemical Action

A secondary cell isalso called a storagecell, because it canbe recharged, or awet cell, because ithas a liquidelectrolyte.

This electrolyte

happens to be asolution of sulfuricacid mixed withwater.

Secondary Cell


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Chemical Action

One of the plates is made of zinc, andthe other one is made of copper.

The chemical action between theplates and the electrolyte causes anegative charge to build up on the zincplate and a positive charge to build up

on the copper plate.


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Chemical Action

In both the primary cell and thesecondary cell, a negative charge

builds up on one plate and apositive charge builds up on theother plate.

What the chemical action does,then, is to create a potentialdifference between the two plates.


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Chemical Action

A potentialdifference isvoltage;therefore, thechemical actionproduces voltage

in a battery.


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Chemical Action

When a battery is made up ofmore than one cell, the cells are

usually connected in series. Because the cells are connected in

this way, the voltages produced

by the individual cells can beadded to get the total voltageproduced by the battery.


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Magnetism

Magnetism is the mostimportant of the sixways of producingvoltage, because it'sthe basis of producingmost of the electricitywe use.

The power plant

generators usemagnetism to convertmechanical energyinto electrical energy.

Voltage Produced byMagnetism


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Magnetism

Wheneverelectric currentflows through aconductor, amagnetic field iscreated around

the conductor.


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Magnetism

Whenever a conductor is passed througha magnetic field, magnetism, and themechanical energy needed to pass theconductor through the magnetic fieldproduce a voltage that will cause currentto flow through the conductor.


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Magnetism

In both of these cases, there is aconductor, a magnetic field, and

some kind of motion. Whenever magnetism is used to

produce voltage, all three of these

things have to be present.


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Magnetism

The main thing to remember isthat a conductor, a magnetic field,

and relative motion between theconductor and the magnetic fieldis needed to produce a voltage.

If these three requirements arenot met, no voltage will beproduced.

Common Symbols and


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Common Symbols and

Abbreviations The symbols for voltage, current, andresistance are shown in picture with thecorresponding measurement and

symbol, and a description.

Common Symbols and


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Common Symbols and

AbbreviationsThe common symbol for power is P.

Power is measured in watts and thecommon symbol for watts is W.

Power is the product of current andvoltage.

Power is covered in more detail later in

this section.

Common Symbols and


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Common Symbols andAbbreviations

The common symbol for voltage is acapital E.

The E stands for electromotive force,

which is the difference in potentialbetween a positive charge and anegative charge.

That potential difference is what is

defined as voltage. The unit used to measure voltage is the

volt, which is commonly abbreviatedwith a capital V.

Common Symbols and


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Common Symbols and

Abbreviations The common symbol for current is acapital I.

Current is measured in amperes, or just

amps, for short. One ampere is actually the flow of 6.25

x 1018 electrons past a given point inone second.

Two common abbreviations foramperes are a capital A and a small a.

Common Symbols and


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Common Symbols and

AbbreviationsThe common symbol for

resistance is a capital R.

Resistance is measured in ohms,and the common symbol for ohmsis the Greek letter omega ().

Resistance is the opposition ofcurrent.

Common Symbols and


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Common Symbols and

Abbreviations In a power plant, a resistor is acomponent that is put into a circuit tooppose, or resist, current flow.

If there is more than one resistorplaced in a circuit, they can be labeledwith subscripts: R

1, R

2, etc.

Subscripts can also be used to refer tomore than one component or quantity.


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Mathematical Prefixes

Mathematical prefixes provide shortways to express very large and verysmall numbers.

For example, to write one million volts,use the prefix M and write 1 MV insteadof 1,000,000 V.

A short way to say one million volts isthe term megavolt: the prefix "mega"means one million.


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One million volts can be expressed inmathematical terms as 106 volts,because 106 is equal to one million.

The capital letter K is the symbol forone thousand, so 1,000 amps can bewritten as 1Ka.

The prefix for one thousand is "kilo,"so one kiloamp can be used instead ofone thousand amps.


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A small letter m is used to representthe fraction one thousandth.

So, for example, 1mV can bewritten for one one thousandth of avolt.

The prefix for one thousandth is

"milli," so one one thousandth of avolt is one millivolt.

Current Voltage and


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Current, Voltage, and

Resistance: Ohm's Law The relationship between current,voltage, and resistance is given byOhms law.

This law states that the amount ofcurrent passing through a conductor isdirectly proportional to the voltage

across the conductor and inverselyproportional to the resistance of theconductor.


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Current Voltage and


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Resistance: Ohm's Law I = E/R can also be written R = E/Iand E = IR.

If any two of the quantities areknown, the third can be calculated.

The formula I = E/R is just aconvenient way of stating that

current is equal to voltage dividedby resistance.

Current Voltage and


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Resistance: Ohm's Law Ohm's Law can be very useful for

predicting what will happen to one of

the three quantities when one of theothers changes.

For example, if the resistance in acircuit remains constant, current willincrease when voltage increases, andcurrent will decrease when voltagedecreases.



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Current, Voltage, andResistance: Ohm's Law

Look at the exampleof a circuit wherethe voltage is 10

volts and theresistance is 10ohms.

Using Ohms Law

the current is I =E/R, I = 10/10, I = 1amp.


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Current Voltage and


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Resistance: Ohm's LawThe only difference between the

circuit shown in the first example

and the circuit shown in thesecond example is the voltage.

When the voltage doubled, from

10 volts to 20 volts, the currentalso doubled, from 1 amp to 2amps.

Current Voltage and


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Resistance: Ohm's Law This is expected since Ohm's Law

states that current is directly

proportional to voltage. When voltage increases or

decreases, current increases or

decreases proportionately as longas resistance does not change.

Current Voltage and


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Resistance: Ohm's Law Ohm's Law also states that current

is inversely proportional to

resistance.This means that when resistance

increases, current decreases, and

when resistance decreases,current increases, as long asvoltage does not change.

Current Voltage and


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Resistance: Ohm's Law The amount of resistance in a circuit

can be changed by adding or taking out

resistors. Adding resistors increases the

resistance in a circuit and decreases

the current. Taking out resistors decreases the

resistance and increases the current.

Series Circuits and Parallel


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Circuits A series circuit is an electrical circuitwith a single current path.

A parallel circuit is an electrical circuitwith two or more parallel current paths.

It is also possible to have circuits thatare part series and part parallel.

Such circuits are called series parallelcircuits.



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Circuits The main differences betweenseries circuits and parallel circuits

are in how the components arearranged and how voltage andcurrent are distributed and iscovered in the following.

Series Circuits


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Series Circuits

When electrical circuits arearranged to form a single

conducting path between theterminals of a source of electriccurrent, the circuits are said to beconnected in series.


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Series Circuits

Current flows from thenegative terminal ofthe power source,through each of the

components in thecircuit, to the positiveterminal of the powersource.

All the components ina series circuit have tobe either on or off atthe same time.

Series Circuit


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Series Circuits

If one of the light bulbs inthe circuit in the pictureburns out, the currentpath will be interrupted,

and all the other lightbulbs will go out.

This fact is true for allseries circuits: If onecomponent is off, the

current path is broken, soall other components areoff.

Series Circuit

l i i i


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Voltage in a Circuit

Voltage can be thought of as being used upby the loads in a circuit.

The voltage that each load uses up is called

the voltage drop across that load. Voltage drop can be calculated from the

equation E = IR, where E is the voltage dropacross the object, I is the amount of current,

and R is the resistance of the object.

S i Ci i O


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Series Circuits: Fact One

In a series circuit with oneresistor, the voltage drop across

that resistor is equal to the sourcevoltage.

S i Ci i F T


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Series Circuits: Fact Two

In a series circuit with two or moreresistors, the voltage drop across

each resistor is directlyproportional to the resistance ofthe resistor.

S i Ci i F Th


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Series Circuit: Fact Three

The sum of the voltage dropsacross each resistor in a series

circuit is equal to the sourcevoltage.

S i Ci it F t F


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Series Circuit: Fact Four

The total resistance in a seriescircuit is equal to the sum of the

individual resistances. If three components with

resistances R1, R2, and R3 are

connected in series, their totalresistance is R1 + R2 + R3.

S i Ci it F t Fi


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Series Circuit: Fact Five

The series circuit only has onecurrent path; therefore, the

current in a series circuit is thesame through all the componentsin the circuit.

P ll l Ci it


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Parallel Circuits

A parallel circuitis an electricalcircuit with two

or more parallelcurrent paths.

The current

paths are oftencalled branches,or legs.

Resistors in Parallel

P ll l Ci it


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Parallel Circuits

If various components are connected toform separate paths between theterminals of a source of electric

current, they are said to be connectedin parallel.

Current from the source splits up andenters the various branches.

After flowing through the separatebranches, the current merges againbefore reentering the current source.

P ll l Ci it


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Parallel Circuits

Each path, or branch, splits awayfrom the main circuit and then

joins it again later on. In a parallel circuit, current still

flows from the negative terminalof the power source to the positiveterminal.

P ll l Ci it


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Parallel Circuits

However, in a parallel circuit, thecurrent does not have to flow

through each component. In the circuit, two of the light

bulbs could burn out, and therewould still be a complete currentpath through the branch with thethird bulb in it.

P ll l Ci it


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Parallel Circuits

To understand parallel circuits, there arethree facts to remember: The voltage across each branch of a parallel

circuit is equal to the source voltage. The total current in a parallel circuit is equal

to the sum of the currents in each branch.

The total resistance in a parallel circuit is less

than the resistance in any of the branches.

P ll l Ci it


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Parallel Circuits

The total resistance of objectsconnected in parallel is less than thatof any of the individual resistances.

This is because a parallel circuit offersmore than one branch (path) for theelectric current, whereas a series

circuit has only one path for all thecurrent.

P ll l Ci it


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Parallel Circuits

The electric currentthrough a parallelcircuit is distributedamong the branches

according to theresistances of thebranches.

If each branch hasthe same resistance,then the current ineach will be equal.

Resistors in Parallel

Parallel Circuits


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Parallel Circuits

If the branches have differentresistances, the current in each

branch can be determined from theequation I = E/R: Where I is the amount of current in the

branch,

E is the voltage, and

R is the resistance of the branch.

Parallel Circuits


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Parallel Circuits

The total resistance of a parallelcircuit can be calculated from the

equation: 1/R = 1/R1 + 1/R2 = 1/R3 +. Where R is the total resistance, and

R1, R2, R3,.... are the resistances of thebranches.

Series Parallel Circuits


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Series Parallel Circuits

Many circuitscombine seriesand parallel

arrangements. One branch of a

parallel circuit,for example, may

have within itseveral objects ina series.

Combination Circuit

Power


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Power

Electrical power is the rate atwhich work is done by electricalenergy.

In order to produce power, bothvoltage and current are needed.

Voltage provides the force andcurrent provides the rate andmotion.

Power


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Power

A basic formula used to figure power isP = EI.

Power (P) is equal to voltage (E) times

current (I). The basic unit for measuring power is

the watt.

For a circuit with the source voltage at

5 volts and the total current is 1 amp,then there is 5 watts of power:

P = EI, P = 5 x 1, P = 5 watts.

Power


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Power

The basic unit for power use over aperiod of time is the watt hour.

The watt hour is a relatively small unit,and is not practical for measuring the

amount of power used in homes andbusinesses.

A kilowatt hour is equal to onethousand watt hours.

Most meters that are used in homesand businesses are calibrated inkilowatt hours.

Power


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Power

There are two methods for calculating theamount of power used in series andparallel circuits: Multiply the source voltage by the total

current in the circuit: P = EI Add the power used by each device in the

circuit.

The methods for calculating power are the

same for series and parallel circuits, thefiguring is different for the two types ofcircuits.

Magnetism


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Magnetism

What is calledmagnetism is reallymany lines of force.

Although it isimpossible to seethese lines of force,it is possible to seethe effects that theyhave on certainmaterials.

Magnetic Lines of Force

Magnetism


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Magnetism

Magnetism is oneof the basicmethods of

producingelectricity.

To understandmagnetism is to

understand howmotors andgenerators work.

Magnetism


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Magnetism

A conductor, amagnet, and relativemotion will producea voltage, and this

voltage can be usedto produce current.

A magnetic field canbe created bypassing currentthrough aconductor.

Magnetism


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Magnetism

The four basic properties associatedwith magnetism are: Only certain metals can be magnetized.

Magnetic lines of force flow from one endof a magnet to the other.

The ends of magnets have the ability toattract or repel each other.

Certain metals have the ability to becometemporary magnets.

Magnetism


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Magnetism

The lines of forcein a magneticfield always flow

from one end ofa magnet to theother.

Magnetism


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Magnetism

The two ends ofa magnet arecalled the north

pole and thesouth pole.

Magnetism


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Magnetism

Lines of force, orlines of flux,always flow from

the north pole tothe south pole onthe outside of amagnet and

complete the loopon the inside.

Magnetism


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Magnetism

The strength of amagnetic field isdetermined by howmany lines of fluxthere are and howclose together theyare: the closer thelines of flux, the

greater the strengthof the magneticfield.

Magnetism


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g

Magnetic poles have the ability toattract or repel each other.

Opposite magnetic poles attract eachother, and like magnetic poles repel

each other. The term "pole" is used to indicate the

two ends of a magnet.

The polarity of a magnet refers to theopposite powers contained in themagnet's poles.

Magnetism


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Magnetism

The final property of magnetism isthat certain metals have theability to become temporarymagnets.

A temporary magnet is a magnetthat will hold its magneticproperties for only a short time.

Electromagnets


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Electromagnets

An electromagnetis a magnet that isproduced when

current is passedthrough aconductor.

Electromagnets


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Electromagnets

If the current isswitched on and off,the electromagnetturns on and off.

Being able to turn amagnet on or off asneeded isimportant, becauseit provides a meansfor controllingmagnetism.

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Electromagnets

Controlledmagnetism is thebasic principlebehind the operationof motors, solenoids,generators, relaysand other electricaldevices.

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Electromagnets

If a wire is bent intomany continuousloops to form a longspiral coil, then the

magnetic lines offorce tend to gothrough the centerof the coil from oneend to the other

rather than aroundthe individual loopsof wire.

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Electromagnets

Such a coil,called a solenoid,behaves in the

same way as amagnet and isthe basis for allelectromagnets.

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Electromagnets

The end fromwhich the linesexit is the north

pole and the endinto which thelines reenter isthe south pole.

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Electromagnets

The polarity of the coil can bedetermined by applying theleft-hand coil rule.

If the left hand grasps the coilin such a way that the fingerscurl around in the direction ofthe electron current, then thethumb points in the directionof the north pole and thedirection of the flow of the

magnetic field flux lines.

Electromagnets


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Electromagnets

This rule is agood one toremember when

you're workingwith motors andgenerators.

Electromagnets


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Electromagnets

When current issent through asolenoid, the

current and themagnetic fieldproducedbehaves in aspecific way inrelation to eachother.

Electromagnets


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Electromagnets

Current always flows through a circuit fromthe negative terminal of the power sourceto the positive terminal.

If the polarity of the power source isreversed, the direction of flow of themagnetic lines of flux will reverse, also.

In addition to controlling whether or not an

electromagnet exists, the strength of itsmagnetic field can also be controlled.

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Electromagnets

The three ways to increase thestrength of an electromagnet'smagnetic field are: Increasing the current flowing through

the conductor

Forming the conductor into a coil

Adding a metal core to the coil

Electromagnets


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Electromagnets

Since the strength of the magneticfield is related to the currentflowing through the conductor,then increasing the current in theconductor will increase thestrength of the magnetic field.

Electromagnets


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Electromagnets

The second method is to form thesolenoid into a coil.

With a straight, only one magneticfield is produced.

Electromagnets


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Electromagnets

When the conductor is formed into acoil; each turn of the conductor createsan additional magnetic field.

The additional magnetic fields acttogether to produce one larger,stronger magnetic field.

The more turns in a conductor, thestronger the magnetic field.

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Electromagnets

Finally, a metal core, such as aniron bar, can be added to the coilto further increase the strength ofthe magnetic field.

The metal core concentrates anddirects the lines of flux, thusincreasing the magnetic field'sstrength.

Electromagnets


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Electromagnets

To determine the field strength of anelectromagnet, the number of turns ismultiplied in the conductor by the

amount of current (in amperes) flowingthrough the coil.

The result is the field strength of the

electromagnet expressed in unitscalled ampere turns.

Alternating Current


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Alternating Current

Alternating current (AC)electricity is different fromthe direct current (DC)electricity in that it moves

back and forth instead offlowing directly throughthe wire.

AC is the electricity thatpowers our homeappliances, lights,televisions and computers.

Alternating Current


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Alternating Current


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Alternating Current

Most electric power stationssupply electricity in the form ofalternating currents.

The current flows first in onedirection, builds up to a maximumin that direction, and dies down tozero.

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e a g Cu e

It then immediately starts flowingin the opposite direction, builds upto a maximum in that direction,and again dies down to zero.

Then it immediately starts in thefirst direction again. This surgingback and forth can occur at a veryrapid rate.

Alternating Current


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g

Two consecutive surges, one in eachdirection, are called a cycle.

The number of cycles completed by an

electric current in one second is calledthe frequency of the current.

In the United States and Canada, mostcurrents have a frequency of 60 cyclesper second.

Alternating Current


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g

The rate at which AC cycles arecompleted is known as frequency.

Frequency used to be expressed as

cycles per second. Today, however, the term hertz is

more common.

One hertz is equal to one completevoltage cycle per second.

Electric DistributionSystem


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System

An electric power distribution systemconsists of six main components: The power station, a set of transformers to

raise the generated power to the high

voltages used on the transmission lines. The transmission lines, the substations atwhich the power is stepped down to thevoltage on the distribution lines.

The transformers, to lower the voltage to the

level used by the consumer's equipment. The distribution lines, transfers power to the

customers.

Power Station (Plant)


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( )

The power station of a power systemconsists of a prime mover, such as aturbine, driven by water, steam orcombustion gases.

The turbine(s) drives the generator(s).

The electricity produced by thegenerator(s) is routed to a high voltage

switchyard. From the high voltage switchyard, the

electricity is distributed to the user.

Transformers


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The electric powersystems usetransformers toconvert electricity intodifferent voltages.

A transformer is anelectromagnetic thatis made by wrapping awire around a iron rodand using ACelectricity.

Transformers


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The magnetic field will alternate atthe same rate as the electriccurrent changes.

If another wire is wrapped aroundthe rod, the changing magneticfield will create an AC current in

that wire.

Transformers


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What is especially interestingabout this phenomenon is that thevoltage created in the second wiredepends not only on the voltage inthe first wire but also on the ratioof the number of turns around the

iron rod.

Transformers


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This type of ACelectromagnet withtwo sets of wires iscalled a transformer.

The AC transformeris a way to easilychange the voltageof the electricity,something that can't

be done with DCelectricity.

Transformers


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This gives AC atremendousadvantage over

DC as a source ofelectricity,because of theability to easily

transform voltageup or down.

Transformers


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With transformers,each stage of thesystem can beoperated at an

appropriate voltage. In a typical system,

the generators atthe power stationdeliver a voltage of

from 1,000 to26,000 volts (V).

Transformers


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Transformers step this voltage upto values ranging from 138,000 to765,000 V for the long-distanceprimary transmission line becausehigher voltages can betransmitted more efficiently over

long distances.

Transformers


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At the substation the voltage may betransformed down to levels of 69,000 to138,000 V for further transfer on thedistribution system.

Another set of transformers step thevoltage down again to a distribution levelsuch as 2,400 or 4,160 V or 15, 27, or 33kilovolts (kV).

Finally the voltage is transformed onceagain at the distribution transformer nearthe point of use to 240 or 120 V.

Transmission Lines


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The lines of high-voltage transmissionsystems are usuallycomposed of wires ofcopper, aluminum, orcopper-clad oraluminum-clad steel,which are suspendedfrom tall latticeworktowers of steel by

strings of porcelaininsulators.

Transmission Lines


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By the use of clad steel wires andhigh towers, the distance betweentowers can be increased, and thecost of the transmission line isreduced.

High-voltage lines may be built

with as few as six towers to thekilometer.

Supplemental Equipment


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Any electric-distribution systeminvolves a large amount ofsupplementary equipment to protect

the generators, transformers, and thetransmission lines.

The system often includes devicesdesigned to regulate the voltage orother characteristics of power deliveredto consumers.

Circuit Breakers


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Circuit breakersare used toprotect allelements of a

power systemfrom short circuitsand overloads,and are used for

normal switchingoperations.

Circuit Breakers


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These breakers arelarge switches thatare activatedautomatically in the

event of a shortcircuit or othercondition thatproduces a sudden

rise of current.


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Circuit Breakers


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In large air-type circuit breakers, aswell as in oil breakers, magnetic fieldsare used to break up the current.

Small air-circuit breakers are used forprotection in shops, factories, and inmodern home installations.

In residential electric wiring, fuses wereonce commonly employed for the samepurpose.

Circuit Breakers


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A fuse consists ofa piece of alloywith a low meltingpoint, inserted in

the circuit, whichmelts, breakingthe circuit if thecurrent rises

above a certainvalue.Circuit Breaker

Power Grids


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In most parts ofthe world, localor national

electric utilitieshave joined ingrid systems

Power Grids


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The linking grids allow electricitygenerated in one area to be sharedwith others.

Each utility that agrees to share gainsan increased reserve capacity, use oflarger, more efficient generators, andthe ability to respond to local powerfailures by obtaining energy from alinking grid.

Power Quality


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In recent years electricity hasbeen used to power moresophisticated and technicallycomplex manufacturingprocesses, computers andcomputer networks, and a variety

of other high-technologyconsumer goods.

Power Quality


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These products and processes aresensitive not only to the continuityof power supply but also to theconstancy of electrical frequencyand voltage.

Power Quality


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Consequently, utilities are takingnew measures to provide thenecessary reliability and quality of

electrical power, such as byproviding additional electricalequipment to assure that the

voltage and other characteristicsof electrical power are constant.

Voltage Regulation


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Long transmission lines haveconsiderable inductance andcapacitance.

When a current flows through the line,inductance and capacitance have theeffect of varying the voltage on the lineas the current varies.

Thus the supply voltage varies with theload.

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Several kinds of devices are used toovercome this undesirable variation in anoperation called regulation of the voltage.

The devices include induction regulatorsand three-phase synchronous motors(called synchronous condensers), both ofwhich vary the effective amount ofinductance and capacitance in the

transmission circuit.

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Inductance and capacitance react with atendency to nullify one another.

When a load circuit has more inductive thancapacitive reactance, as almost invariably

occurs in large power systems, the amountof power delivered for a given voltage andcurrent is less than when the two are equal.

The ratio of these two amounts of power is

called the power factor.

Voltage Regulation


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Because transmission-line losses areproportional to current, capacitance isadded to the circuit when possible, thus

bringing the power factor as nearly aspossible to 1.

For this reason, large capacitors arefrequently inserted as a part of power-

transmission systems.

Power Factor


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The power factor is the ratio of powerdissipated over input: the ratio of theactual power dissipated in an electrical

system to the input power of voltsmultiplied by amps.

Power factor is the relationshipbetween Real (Active) Power (kW) and

Total (Apparent) Power (kVA).

Power Factor


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Essentially, power factor is ameasurement of how efficientlyelectrical power is being used and

is expressed in a decimal orpercentage.

The higher the power factor, the

more efficiently electrical power isbeing used.


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Power Factor


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Real Power andReactive Powertogether make

up what is calledTotal Power.

Total Power isused in the

calculation forthe Power Factor.

Total Power


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Total Power ismeasured inkilovoltampere(kVA).

Total Power is alsocalled ApparentPower and is thecombination of

Real Power andReactive Power.

Real Power


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Real Power (alsocalled Productiveor Active Power)is the actualpower used andactually performsthe work.

Real Power ismeasured inkilowatts (kW).

Reactive Power


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Reactive Powermaintains the electro-magnetic fields forinductive loads.

Reactive Power ismeasured in kilovars(kVAR).

Reactive Power,whether inductive orcapacitive, always acts

at right angles to RealPower.

Reactive Power


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Reactive Power isnot useful in anindustrial setting,

as it does no realwork whensupplied tomotors or other

electricaldevices.

The Power Triangle


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Graphically, thePower Triangleon a system is a

representation ofthe Power Factor.

The Power Triangle


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The following analogy can help in theunderstanding of the power factor.

Imagine a mug of beer that is partliquid and part foam.

The total capacity of the mugrepresents total power (kVA).

The foam represents reactive power(kVAR) and the beer represents real

power (kW). With this analogy the ratio of beer to

mug capacity is the power factor.

The Power Factor Formula


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The basic formula forPower Factor is themathematical ratio of realpower to total power.

This ratio is an effectivemeasure of systemelectrical efficiency and isrepresented as apercentage or decimal.

The power factor formula

is represented in thepicture.

Electric Meters


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Meters arefrequently usedin the plant to

measureelectricalquantities suchas voltage,

current, andresistance.

Voltmeter

Electric Meters


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The three generaltypes of meters are: Ammeter

Voltmeter Ohmmeter

Documents

Fund Course Module 7