Electrical Power Systems Chapter 8 Mill Creek High School G. Burrows

Objectives List the types of current and explain how they are produced List the types of current and explain how they are produced State how electrical power is measured State how electrical power is measured Name different types of electrical circuits Name different types of electrical circuits Identify relationship between electricity and magnetism Identify relationship between electricity and magnetism Describe how atoms act to produce electrical current Describe how atoms act to produce electrical current

Objectives Explain purpose of common electrical components Explain purpose of common electrical components Discuss safety when dealing with live electricity Discuss safety when dealing with live electricity Interpret an electrical circuit Interpret an electrical circuit And do really cool stuff with it. And do really cool stuff with it.

Electrical Systems Use electrical energy to perform work Use electrical energy to perform work Electricity Electricity Most widely used source of energy Most widely used source of energy Most versatile type of energy Most versatile type of energy An essential part of almost EVERY energy power and transportation system An essential part of almost EVERY energy power and transportation system

Atomic Structure Atoms are building block of everything Atoms are building block of everything Made of smaller particles Made of smaller particles Protons: positive electrical charge Electrons: negative electrical charge Neutron: no charge at all

Atomic Structure Center of the atom has the protons and neutrons Center of the atom has the protons and neutrons Electrons travel around in elliptical paths Electrons travel around in elliptical paths # of electrons = # of protons # of electrons = # of protons Each electron follows a different path called “rings.” Each electron follows a different path called “rings.”

Atoms Atoms remain stable when electrons = protons Atoms remain stable when electrons = protons They lose or gain electrons to remain stable They lose or gain electrons to remain stable Electrons in “valance ring” (outermost) are the ones that are gained or lost Electrons in “valance ring” (outermost) are the ones that are gained or lost

Conductors & Insulators Conductors: are made up of atoms that can easily shed and gain electrons Conductors: are made up of atoms that can easily shed and gain electrons Insulators: are made up of atoms that do not easily transfer electrons Insulators: are made up of atoms that do not easily transfer electrons Semi-conductors: are both conductors and insulators Semi-conductors: are both conductors and insulators

Electron Theory and Current Normally atoms are neutral Normally atoms are neutral When electrons are forced free electricity is produced When electrons are forced free electricity is produced Electron Theory: electrons flow from a negative point to a positive point Electron Theory: electrons flow from a negative point to a positive point

Current DC: direct current-electrons always move in only one direction DC: direct current-electrons always move in only one direction Can be stored in batteries Can be stored in batteries AC: alternating current-electrons flow in one direction and then reverse and flow the other way AC: alternating current-electrons flow in one direction and then reverse and flow the other way Can be transmitted a long way Can be transmitted a long way

Effort, Rate and Opposition Effort is the (voltage) … force behind the movement of electrons Effort is the (voltage) … force behind the movement of electrons Marbles in a garden hose …… Marbles in a garden hose …… Voltage is the force pushing the marbles through the hose Voltage is the force pushing the marbles through the hose Amperage is the # of marbles Amperage is the # of marbles Resistance to flow is called Ohms Resistance to flow is called Ohms

Electrical Circuits The heart of any electrical system The heart of any electrical system Must have Must have Power source Power source Load Load Conductors Conductors The current must flow in a complete path The current must flow in a complete path

Schematics Easier to describe it graphically than in words Easier to describe it graphically than in words “a picture is worth a 1000 words” “a picture is worth a 1000 words” Like a road map Like a road map Symbols represent components Symbols represent components

Some Common Symbols Insert picture 8-11

Circuits Closed circuit: complete and will function properly Closed circuit: complete and will function properly Open circuit: not energized (by switch or by accident) Open circuit: not energized (by switch or by accident) Continuity: continuous flow through a component Continuity: continuous flow through a component

Laws That Describe Electricity Ohms’ law: voltage will be determined by multiplying current (I) by Resistance (R) Ohms’ law: voltage will be determined by multiplying current (I) by Resistance (R) E=Voltage E=Voltage R=Resistance R=Resistance I=Current I=Current

Watt’s Law AKA …. The electrical power formula AKA …. The electrical power formula P= Wattage P= Wattage E=Voltage E=Voltage I=Current (amps) I=Current (amps)

Kilowatt-Hours Billing of electrical power is done in (kWh) Billing of electrical power is done in (kWh) Includes wattage and time used Includes wattage and time used 1kWh will power 1kWh will power One 1000W heater running for one hour One 1000W heater running for one hour Ten 100W bulbs running for one hour Ten 100W bulbs running for one hour One 2000W heater running for 30 minutes One 2000W heater running for 30 minutes One 4000W AC unit running for 15-minutes One 4000W AC unit running for 15-minutes

kWh kWh= (watts x hours) / 1000 kWh= (watts x hours) / 1000 Cost 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 and electricity cost $.09/kWh. How much would it cost to light the bulbs for a workweek Twelve 100W bulbs are on 7.5 hours per day and electricity cost $.09/kWh. How much would it cost to light the bulbs for a workweek 1200W x 7.5hr X 5 days = Watt-hours 1200W x 7.5hr X 5 days = Watt-hours Watt-hours/1000 = 45 kWh Watt-hours/1000 = 45 kWh 45 kWh x $.09/kWh = 4.05 for the week 45 kWh x $.09/kWh = 4.05 for the week

Residential kWh Watt-Hour Meter Watt-Hour Meter Figure 8-16 Figure s, 1000s, 100s, 100s, 10s, 10s, 1s, 1s, 10ths 10ths

Circuits Series circuits Series circuits One continuous path for current One continuous path for current One break in the circuit and the whole one is useless One break in the circuit and the whole one is useless Resistance is added together Resistance is added together R T = R 1 + R 2 + R 3 … R T = R 1 + R 2 + R 3 … Amperage is the same anywhere in circuit Amperage is the same anywhere in circuit

Circuits Parallel Circuits Parallel Circuits More than one path for the electrons to flow More than one path for the electrons to flow One break will only shut off some of the lights One break will only shut off some of the lights Kirchoff’s voltage law says that voltages across each branch of a parallel circuit are equal Kirchoff’s voltage law says that voltages across each branch of a parallel circuit are equal Adding more loads decreases total resistance because there are more pathways Adding more loads decreases total resistance because there are more pathways

Magnetism & Electricity The two can affect each other The two can affect each other Electric current produces magnetism Electric current produces magnetism Magnets can induce or cause electrical current in conductors Magnets can induce or cause electrical current in conductors Magnet is any material attracted to metal containing iron Magnet is any material attracted to metal containing iron Motor and generator Motor and generator

Electromagnets A conductor wrapped around an iron core. A conductor wrapped around an iron core. Ends of conductor are attached to power source Ends of conductor are attached to power source Iron core becomes magnetized Iron core becomes magnetized

Electromagnetic Induction Creating electricity through the use of magnets Creating electricity through the use of magnets As conductors are passed through magnetic field, electrons are forced from atoms creating electricity As conductors are passed through magnetic field, electrons are forced from atoms creating electricity

Electrical Power Sources Cells and batteries: Cells and batteries: Cells are a common way of storing electrical power (mistakenly called a battery) Cells are a common way of storing electrical power (mistakenly called a battery) Battery: is made up of a bank of cells put together Battery: is made up of a bank of cells put together All cells and batteries produce DC current All cells and batteries produce DC current They convert Chemical Energy to Electrical Energy They convert Chemical Energy to Electrical Energy

Typical Battery

AC Generators Converts mechanical energy into electrical energy (AKA: alternator) Converts mechanical energy into electrical energy (AKA: alternator) Produces electricity through induction Produces electricity through induction Produces AC electricity Produces AC electricity

DC Generators Relies on Electromagnetic induction just like AC Generators Relies on Electromagnetic induction just like AC Generators Slightly different set up (internally) so that current does not alternate its flow as the Armature loop spins Slightly different set up (internally) so that current does not alternate its flow as the Armature loop spins

Controlling Electricity Switches: Switches: Single-pole, single throw (SPST) Single-pole, single throw (SPST) Opens or closes one set of contacts to turn load on and off Opens or closes one set of contacts to turn load on and off Single-pole, Double throw (SPDT) Single-pole, Double throw (SPDT) Used to turn lights on and off from different ends of hall or stairs (aka: 3-way switch) Used to turn lights on and off from different ends of hall or stairs (aka: 3-way switch)

Controlling Electricity Switches: (Continued) Switches: (Continued) Momentary contact switches: only closes or opens circuit when held down Momentary contact switches: only closes or opens circuit when held down PBNO-Push Button Normal Open PBNO-Push Button Normal Open PBNC-Push Button Normal Close PBNC-Push Button Normal Close PBMB-Push Button Make Break (clicks on and clicks off) PBMB-Push Button Make Break (clicks on and clicks off)

Controlling Electricity Diodes: only allow electricity to flow in one direction Diodes: only allow electricity to flow in one direction Transformers: used to increase or decrease voltage Transformers: used to increase or decrease voltage Step-down transformer: reduces voltage Step-down transformer: reduces voltage Step-up transformer: increases voltage Step-up transformer: increases voltage

Transformers Figure 8-39

Transformers Just like a gear set Just like a gear set Increase effort (voltage) while decreasing rate (amperage) Increase effort (voltage) while decreasing rate (amperage) Cannot produce more power it just changes the characteristics of it Cannot produce more power it just changes the characteristics of it Figure 8-39

Protecting Electrical Circuitry Fuses: made of a filament that breaks if too much current (amperage) passes through it Fuses: made of a filament that breaks if too much current (amperage) passes through it Circuit Breaker: Same function as fuse, but can be reset Circuit Breaker: Same function as fuse, but can be reset

GFCIs GFCI: Ground Fault Circuit Interrupter can trip to open a circuit like a breaker but much more sensitive. GFCI: Ground Fault Circuit Interrupter can trip to open a circuit like a breaker but much more sensitive. Monitors flow and trips if there is a 6-Milli- amp short. (not life threatening) Monitors flow and trips if there is a 6-Milli- amp short. (not life threatening)

Electrical Safety 20% of electrical deaths each year are due to faulty household wiring 20% of electrical deaths each year are due to faulty household wiring Rules: Rules: Use appropriate size fuse Use appropriate size fuse Don’t assume that breaker will protect you from excessive amperage Don’t assume that breaker will protect you from excessive amperage Trouble shoot with power off Trouble shoot with power off Drain all capacitors Drain all capacitors Ensure GFCI is installed Ensure GFCI is installed Do not Ground Yourself!!!! Electricity flows to ground Do not Ground Yourself!!!! Electricity flows to ground