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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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Electrons and Electrical
Charge A typical atom
has a nucleus in
its center. The nucleus is
composed of twodifferent types of
tiny particles:protons andneutrons.
Atom with Electron in Orbit
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Electrons and Electrical
Charge Other tiny
particles, called
electrons, orbitaround thenucleus.
Atom with Electron in Orbit
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Electrons and Electrical
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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Electrons and Electrical
Charge Of the three
types of particles
in atoms, onlytwo of them,protons andelectrons, are
important in thestudy ofelectricity.
Atom with Electron in Orbit
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Electrons and Electrical
Charge Protons and electrons are "charged"
particles, which means that they react
electrically.
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Electrons and Electrical
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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Charging by Induction
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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Charging by Induction
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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Charging by Induction
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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Sources of Electric Current
Generatorsproduce electricity
via magnetism.
Electrolytic cellsuse chemical
energy to produceelectricity.
Magnetism
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Sources of Electric Current
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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Simple Circuit with Load
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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Simple Circuit with Load
The battery inthe circuit is the
voltage source. The voltage
produced by thebattery pushes
current throughthe circuit.
Circuit with Load
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Simple Circuit with Load
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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Simple Circuit with Load
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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Conductors and Insulators
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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Conductors and Insulators
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.
Electricity Produced by Compressing
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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.
Electricity Produced by Compressing
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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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Mathematical Prefixes
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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Mathematical Prefixes
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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Current, Voltage, and
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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Current, Voltage, and
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.
Current, Voltage, and
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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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Current, Voltage, and
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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Current, Voltage, and
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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Current, Voltage, and
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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Current, Voltage, and
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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Series Circuits and Parallel
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.
Series Circuits and Parallel
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Series Circuits and Parallel
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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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.
Electromagnets
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Electromagnets
Controlledmagnetism is thebasic principlebehind the operationof motors, solenoids,generators, relaysand other electricaldevices.
Electromagnets
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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.
Electromagnets
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Electromagnets
Such a coil,called a solenoid,behaves in the
same way as amagnet and isthe basis for allelectromagnets.
Electromagnets
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Electromagnets
The end fromwhich the linesexit is the north
pole and the endinto which thelines reenter isthe south pole.
Electromagnets
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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.
Electromagnets
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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
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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.
Electromagnets
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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.
Alternating Current
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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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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.
Voltage Regulation
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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.
Voltage Regulation
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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
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