Electrical Power SystemsElectrical Power SystemsChapter 8Chapter 8

Mill Creek High SchoolMill Creek High School

G. BurrowsG. Burrows

ObjectivesObjectives

List the types of current and explain how List the types of current and explain how they are producedthey are produced

State how electrical power is measuredState how electrical power is measuredName different types of electrical circuitsName different types of electrical circuits Identify relationship between electricity Identify relationship between electricity

and magnetismand magnetismDescribe how atoms act to produce Describe how atoms act to produce

electrical currentelectrical current

ObjectivesObjectives

Explain purpose of common electrical Explain purpose of common electrical componentscomponents

Discuss safety when dealing with live Discuss safety when dealing with live electricityelectricity

Interpret an electrical circuitInterpret an electrical circuitAnd do really cool stuff with it.And do really cool stuff with it.

Electrical SystemsElectrical Systems

Use electrical energy to perform workUse electrical energy to perform workElectricityElectricity

Most widely used source of energyMost widely used source of energyMost versatile type of energyMost versatile type of energy

An essential part of almost EVERY energy An essential part of almost EVERY energy power and transportation systempower and transportation system

Atomic StructureAtomic Structure

Atoms are building Atoms are building block of everythingblock of everything

Made of smaller Made of smaller particlesparticles Protons: positive Protons: positive

electrical chargeelectrical charge Electrons: negative Electrons: negative

electrical chargeelectrical charge Neutron: no charge at Neutron: no charge at

allall

Atomic StructureAtomic Structure

Center of the atom has the protons and Center of the atom has the protons and neutronsneutrons

Electrons travel around in elliptical pathsElectrons travel around in elliptical paths# of electrons = # of protons# of electrons = # of protonsEach electron follows a different path Each electron follows a different path

called “rings.”called “rings.”

AtomsAtoms

Atoms remain stable when electrons = Atoms remain stable when electrons = protonsprotons

They lose or gain electrons to remain They lose or gain electrons to remain stablestable

Electrons in “valance ring” (outermost) are Electrons in “valance ring” (outermost) are the ones that are gained or lostthe ones that are gained or lost

Conductors & InsulatorsConductors & Insulators

Conductors: are made up of atoms that Conductors: are made up of atoms that can easily shed and gain electronscan easily shed and gain electrons

Insulators: are made up of atoms that do Insulators: are made up of atoms that do not easily transfer electronsnot easily transfer electrons

Semi-conductors: are both conductors and Semi-conductors: are both conductors and insulatorsinsulators

Electron Theory and CurrentElectron Theory and Current

Normally atoms are neutralNormally atoms are neutralWhen electrons are forced free electricity When electrons are forced free electricity

is producedis producedElectron Theory: electrons flow from a Electron Theory: electrons flow from a

negative point to a positive pointnegative point to a positive point

CurrentCurrent

DC: direct current-electrons always move DC: direct current-electrons always move in only one directionin only one directionCan be stored in batteriesCan be stored in batteries

AC: alternating current-electrons flow in AC: alternating current-electrons flow in one direction and then reverse and flow one direction and then reverse and flow the other waythe other wayCan be transmitted a long wayCan be transmitted a long way

Effort, Rate and OppositionEffort, Rate and Opposition

Effort is the (voltage) … force behind the Effort is the (voltage) … force behind the movement of electronsmovement of electrons

Marbles in a garden hose ……Marbles in a garden hose ……Voltage is the force pushing the marbles Voltage is the force pushing the marbles

through the hosethrough the hoseAmperage is the # of marblesAmperage is the # of marblesResistance to flow is called OhmsResistance to flow is called Ohms

Electrical CircuitsElectrical Circuits

The heart of any electrical systemThe heart of any electrical systemMust haveMust have

Power sourcePower sourceLoadLoadConductorsConductors

The current must flow in a complete pathThe current must flow in a complete path

SchematicsSchematics

Easier to describe it graphically than in Easier to describe it graphically than in wordswords

““a picture is worth a 1000 words”a picture is worth a 1000 words”Like a road mapLike a road mapSymbols represent componentsSymbols represent components

Some Common SymbolsSome Common Symbols

Insert picture 8-11Insert picture 8-11

CircuitsCircuits

Closed circuit: complete and will function Closed circuit: complete and will function properlyproperly

Open circuit: not energized (by switch or Open circuit: not energized (by switch or by accident)by accident)

Continuity: continuous flow through a Continuity: continuous flow through a componentcomponent

Laws That Describe ElectricityLaws That Describe Electricity

Ohms’ law: voltage Ohms’ law: voltage will be determined by will be determined by multiplying current (I) multiplying current (I) by Resistance (R)by Resistance (R)

E=VoltageE=Voltage R=ResistanceR=Resistance I=CurrentI=Current

Watt’s LawWatt’s Law

AKA …. The electrical AKA …. The electrical power formulapower formula

P= WattageP= Wattage E=VoltageE=Voltage I=Current (amps)I=Current (amps)

Kilowatt-HoursKilowatt-Hours

Billing of electrical power is done in (kWh)Billing of electrical power is done in (kWh) Includes wattage and time usedIncludes wattage and time used

1kWh will power1kWh will powerOne 1000W heater running for one hourOne 1000W heater running for one hourTen 100W bulbs running for one hourTen 100W bulbs running for one hourOne 2000W heater running for 30 minutesOne 2000W heater running for 30 minutesOne 4000W AC unit running for 15-minutesOne 4000W AC unit running for 15-minutes

kWhkWh

kWh= (watts x hours) / 1000kWh= (watts x hours) / 1000Cost of Electricity = kWh x (cost/kWh)Cost of Electricity = kWh x (cost/kWh)Example:Example:

Twelve 100W bulbs are on 7.5 hours per day Twelve 100W bulbs are on 7.5 hours per day and electricity cost $.09/kWh. How much and electricity cost $.09/kWh. How much would it cost to light the bulbs for a workweekwould it cost to light the bulbs for a workweek

1200W x 7.5hr X 5 days = 45000 Watt-hours1200W x 7.5hr X 5 days = 45000 Watt-hours45000 Watt-hours/1000 = 45 kWh45000 Watt-hours/1000 = 45 kWh45 kWh x $.09/kWh = 4.05 for the week45 kWh x $.09/kWh = 4.05 for the week

Residential kWhResidential kWh

Watt-Hour MeterWatt-Hour Meter Figure 8-16Figure 8-16 1000s, 1000s, 100s, 100s, 10s, 10s, 1s, 1s, 10ths10ths

CircuitsCircuits

Series circuitsSeries circuitsOne continuous path for currentOne continuous path for currentOne break in the circuit and the whole one is One break in the circuit and the whole one is

uselessuselessResistance is added togetherResistance is added togetherRRTT = R = R11 + R + R22 + R + R33 … …Amperage is the same anywhere in circuitAmperage is the same anywhere in circuit

CircuitsCircuits

Parallel CircuitsParallel CircuitsMore than one path for the electrons to flowMore than one path for the electrons to flowOne break will only shut off some of the lightsOne break will only shut off some of the lightsKirchoff’s voltage law says that voltages Kirchoff’s voltage law says that voltages

across each branch of a parallel circuit are across each branch of a parallel circuit are equalequal

Adding more loads decreases total resistance Adding more loads decreases total resistance because there are more pathwaysbecause there are more pathways

Magnetism & ElectricityMagnetism & Electricity

The two can affect each otherThe two can affect each otherElectric current produces magnetismElectric current produces magnetismMagnets can induce or cause electrical Magnets can induce or cause electrical

current in conductorscurrent in conductorsMagnet is any material attracted to metal Magnet is any material attracted to metal

containing ironcontaining ironMotor and generatorMotor and generator

ElectromagnetsElectromagnets

A conductor wrapped around an iron core.A conductor wrapped around an iron core.Ends of conductor are attached to power Ends of conductor are attached to power

sourcesource Iron core becomes magnetizedIron core becomes magnetized

Electromagnetic InductionElectromagnetic Induction

Creating electricity through the use of Creating electricity through the use of magnetsmagnets

As conductors are passed through As conductors are passed through magnetic field, electrons are forced from magnetic field, electrons are forced from atoms creating electricityatoms creating electricity

Electrical Power SourcesElectrical Power Sources

Cells and batteries: Cells and batteries: Cells are a common way of storing electrical Cells are a common way of storing electrical

power (mistakenly called a battery)power (mistakenly called a battery)Battery: is made up of a bank of cells put Battery: is made up of a bank of cells put

togethertogetherAll cells and batteries produce DC currentAll cells and batteries produce DC currentThey convert Chemical Energy to Electrical They convert Chemical Energy to Electrical

EnergyEnergy

Typical BatteryTypical Battery

AC GeneratorsAC Generators

Converts mechanical energy into electrical Converts mechanical energy into electrical energy (AKA: alternator)energy (AKA: alternator)

Produces electricity through inductionProduces electricity through inductionProduces AC electricityProduces AC electricity

DC GeneratorsDC Generators

Relies on Electromagnetic induction just Relies on Electromagnetic induction just like AC Generatorslike AC Generators

Slightly different set up (internally) so that Slightly different set up (internally) so that current does not alternate its flow as the current does not alternate its flow as the Armature loop spinsArmature loop spins

Controlling ElectricityControlling Electricity

Switches:Switches:Single-pole, single throw (SPST)Single-pole, single throw (SPST)

Opens or closes one set of contacts to turn load on Opens or closes one set of contacts to turn load on and offand off

Single-pole, Double throw (SPDT) Single-pole, Double throw (SPDT) Used to turn lights on and off from different ends of Used to turn lights on and off from different ends of

hall or stairs (aka: 3-way switch)hall or stairs (aka: 3-way switch)

Controlling ElectricityControlling Electricity

Switches: (Continued)Switches: (Continued)Momentary contact switches: only closes or Momentary contact switches: only closes or

opens circuit when held downopens circuit when held downPBNO-Push Button Normal OpenPBNO-Push Button Normal OpenPBNC-Push Button Normal ClosePBNC-Push Button Normal ClosePBMB-Push Button Make Break (clicks on and PBMB-Push Button Make Break (clicks on and

clicks off)clicks off)

Controlling ElectricityControlling Electricity

Diodes: only allow electricity to flow in one Diodes: only allow electricity to flow in one directiondirection

Transformers: used to increase or Transformers: used to increase or decrease voltagedecrease voltageStep-down transformer: reduces voltageStep-down transformer: reduces voltageStep-up transformer: increases voltageStep-up transformer: increases voltage

TransformersTransformers

Figure 8-39

TransformersTransformers

Just like a gear setJust like a gear set Increase effort Increase effort

(voltage) while (voltage) while decreasing rate decreasing rate (amperage)(amperage)

Cannot produce more Cannot produce more power it just changes power it just changes the characteristics of the characteristics of itit

Figure 8-39

Protecting Electrical CircuitryProtecting Electrical Circuitry

Fuses: made of a filament that breaks if Fuses: made of a filament that breaks if too much current (amperage) passes too much current (amperage) passes through itthrough it

Circuit Breaker: Same function as fuse, Circuit Breaker: Same function as fuse, but can be resetbut can be reset

GFCIsGFCIs

GFCI: Ground Fault Circuit Interrupter can GFCI: Ground Fault Circuit Interrupter can trip to open a circuit like a breaker but trip to open a circuit like a breaker but much more sensitive.much more sensitive.

Monitors flow and trips if there is a 6-Milli-Monitors flow and trips if there is a 6-Milli-amp short. (not life threatening)amp short. (not life threatening)

Electrical SafetyElectrical Safety

20% of electrical deaths each year are due to 20% of electrical deaths each year are due to faulty household wiringfaulty household wiring

Rules:Rules: Use appropriate size fuseUse appropriate size fuse Don’t assume that breaker will protect you from Don’t assume that breaker will protect you from

excessive amperageexcessive amperage Trouble shoot with power offTrouble shoot with power off Drain all capacitorsDrain all capacitors Ensure GFCI is installedEnsure GFCI is installed Do not Ground Yourself!!!! Electricity flows to groundDo not Ground Yourself!!!! Electricity flows to ground