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Electrical Power Systems Chapter 8. Mill Creek High School G. Burrows. Objectives. List the types of current and explain how they are produced State how electrical power is measured Name different types of electrical circuits Identify relationship between electricity and magnetism
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Electrical Power SystemsChapter 8 Mill Creek High School G. Burrows
Objectives • List the types of current and explain how they are produced • State how electrical power is measured • Name different types of electrical circuits • Identify relationship between electricity and magnetism • Describe how atoms act to produce electrical current
Objectives • Explain purpose of common electrical components • Discuss safety when dealing with live electricity • Interpret an electrical circuit • And do really cool stuff with it.
Electrical Systems • Use electrical energy to perform work • Electricity • Most widely used source of energy • Most versatile type of energy • An essential part of almost EVERY energy power and transportation system
Atomic Structure • Atoms are building block of everything • 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 • Electrons travel around in elliptical paths • # of electrons = # of protons • Each electron follows a different path called “rings.”
Atoms • Atoms remain stable when electrons = protons • They lose or gain electrons to remain stable • 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 • Insulators: are made up of atoms that do not easily transfer electrons • Semi-conductors: are both conductors and insulators
Electron Theory and Current • Normally atoms are neutral • When electrons are forced free electricity is produced • Electron Theory: electrons flow from a negative point to a positive point
Current • DC: direct current-electrons always move in only one direction • Can be stored in batteries • AC: alternating current-electrons flow in one direction and then reverse and flow the other way • Can be transmitted a long way
Effort, Rate and Opposition • Effort is the (voltage) … force behind the movement of electrons • Marbles in a garden hose …… • Voltage is the force pushing the marbles through the hose • Amperage is the # of marbles • Resistance to flow is called Ohms
Electrical Circuits • The heart of any electrical system • Must have • Power source • Load • Conductors • The current must flow in a complete path
Schematics • Easier to describe it graphically than in words • “a picture is worth a 1000 words” • Like a road map • Symbols represent components
Some Common Symbols Insert picture 8-11
Circuits • Closed circuit: complete and will function properly • Open circuit: not energized (by switch or by accident) • Continuity: continuous flow through a component
Laws That Describe Electricity • Ohms’ law: voltage will be determined by multiplying current (I) by Resistance (R) • E=Voltage • R=Resistance • I=Current
Watt’s Law • AKA …. The electrical power formula • P= Wattage • E=Voltage • I=Current (amps)
Kilowatt-Hours • Billing of electrical power is done in (kWh) • Includes wattage and time used • 1kWh will power • One 1000W heater running for one hour • Ten 100W bulbs running for one hour • One 2000W heater running for 30 minutes • One 4000W AC unit running for 15-minutes
kWh • kWh= (watts x hours) / 1000 • Cost of Electricity = kWh x (cost/kWh) • 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 • 1200W x 7.5hr X 5 days = 45000 Watt-hours • 45000 Watt-hours/1000 = 45 kWh • 45 kWh x $.09/kWh = 4.05 for the week
Residential kWh • Watt-Hour Meter • Figure 8-16 • 1000s, • 100s, • 10s, • 1s, • 10ths
Circuits • Series circuits • One continuous path for current • One break in the circuit and the whole one is useless • Resistance is added together • RT = R1 + R2 + R3 … • Amperage is the same anywhere in circuit
Circuits • Parallel Circuits • More than one path for the electrons to flow • 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 • Adding more loads decreases total resistance because there are more pathways
Magnetism & Electricity • The two can affect each other • Electric current produces magnetism • Magnets can induce or cause electrical current in conductors • Magnet is any material attracted to metal containing iron • Motor and generator
Electromagnets • A conductor wrapped around an iron core. • Ends of conductor are attached to power source • Iron core becomes magnetized
Electromagnetic Induction • Creating electricity through the use of magnets • As conductors are passed through magnetic field, electrons are forced from atoms creating electricity
Electrical Power Sources • Cells and batteries: • Cells are a common way of storing electrical power (mistakenly called a battery) • Battery: is made up of a bank of cells put together • All cells and batteries produce DC current • They convert Chemical Energy to Electrical Energy
AC Generators • Converts mechanical energy into electrical energy (AKA: alternator) • Produces electricity through induction • Produces AC electricity
DC 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
Controlling Electricity • Switches: • Single-pole, single throw (SPST) • Opens or closes one set of contacts to turn load on and off • Single-pole, Double throw (SPDT) • Used to turn lights on and off from different ends of hall or stairs (aka: 3-way switch)
Controlling Electricity • Switches: (Continued) • Momentary contact switches: only closes or opens circuit when held down • PBNO-Push Button Normal Open • PBNC-Push Button Normal Close • PBMB-Push Button Make Break (clicks on and clicks off)
Controlling Electricity • Diodes: only allow electricity to flow in one direction • Transformers: used to increase or decrease voltage • Step-down transformer: reduces voltage • Step-up transformer: increases voltage
Transformers Figure 8-39
Transformers • Just like a gear set • Increase effort (voltage) while decreasing rate (amperage) • 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 • 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. • 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 • Rules: • Use appropriate size fuse • Don’t assume that breaker will protect you from excessive amperage • Trouble shoot with power off • Drain all capacitors • Ensure GFCI is installed • Do not Ground Yourself!!!! Electricity flows to ground