Electrical Power Systems Chapter 8

1. Electrical Power SystemsChapter 8 Mill Creek High School G. Burrows

2. 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

3. 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.

4. 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

5. 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

6. 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.”

8. 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

9. 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

10. 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

11. 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

12. 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

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

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

15. Some Common Symbols Insert picture 8-11

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

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

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

19. 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

20. 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

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

23. 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

25. 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

27. 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

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

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

30. 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

31. Typical Battery

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

33. 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

34. 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)

36. 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)

37. 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

38. Transformers Figure 8-39

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

40. 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

41. 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)

42. 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