Presentation Transcript

1. ElectricityIntroduction

2. Electricity Current Four (4) requirements for an electrical current. An abundance of electrons (-) A scarcity of electrons (+) A conducting material The conducting material connecting the area of abundance and the area of scarcity.
3. Electrical Current--cont. Four common methods of developing a surplus of electrons: Electromechanical Electrochemical Thermoelectrical Photoelectrical
4. 1. Electromechanical Generators and alternators are electromechanical devices. An electromechanical device produces electricity when it rotates. Generators/alternators produce electricity through electromagnetic induction. What are the four (4) common sources of power to rotate generators and alternators? How efficient is a generator in converting mechanical power to electricity?
5. 2. Electrochemical Electrochemical reactions can either produce electricity, or use electricity. Chemical reaction produces a voltage A voltage causes a chemical reaction
6. 3. Thermoelectrical Thermoelectrical devices can either uses electricity to produce heat, or use heat to produce electricity. An electric heater produces heat using electricity. A thermocouple uses a heat to produce electricity. How efficient is an electric heater in converting electricity to heat?
7. 4. Photoelectrical Photoelectricity is the emission of electrons from materials upon absorption of electromagnetic radiation. How efficient is a good quality PV cell? Photovoltaic Cell (PV Cell)
8. Electrical current—cont. Electric generator Electric motor There are three (3) components of electrical/mechanical systems currents, magnetic fields and motion. Different combinations have different outcomes.
9. Electrical Theory - Summary Electricity is a form of energy that can produce light, heat, magnetism, chemical changes andmotion. Light occurs when electricity passes through a filament. Heat is produced when electricity flows through a resistance. A magnet field forms around any conductor carrying electricity. Electricity passing through water causes the hydrogen and oxygen to split. Like poles repel each other (motor)

10. Principles of Electricity

11. Introduction Electricity is the primary source of power for stationary equipment. A basic understanding of the principles of electricity is a requirement for using electrical powered equipment efficiently and safely.
12. Electrical Terms Resistance Amperes Volts Ohms law Conductor Insulator Electrical circuit Series circuit Parallel circuit AC current DC current Electrical power Electrical energy Resistance loads Reactant loads Power Factor To understanding electricity you must know and be able to explain the following sixteen (16) electrical terms:
13. 1. Resistance Resistance: a measure of the difficulty encountered by the electrons as they flow through a conductor. Resistance is a characteristic of all materials. Electricity passing through a resistance causes heat. Resistance is measured in units of Ohms () An Ohm is defined as the resistance between two points of a conductor when a constant potential difference of 1 volt, applied to these points, produces a current of 1 ampere. Why do the connections on a extension cord get hot?
14. 2. Amperes Amperes: the measure of the rate of current flow. What does the rate of flow mean? 1 amp = 6.24 × 1018 electrons per second A current (amperage) occurs whenever there is a source of electricity, conductors and a complete circuit. Standard domestic circuits are fused at 15 or 20 amps. What does this mean?
15. 3. Volts Voltage (E or V): the electromotive force (potential) available to cause electrons to flow. What does the term potential mean? Voltage is always measured by comparing the difference (potential) between two points. Standard domestic current is 120V. Are all U.S. electrical circuits 120V? What is the unit of measure for voltage?
16. 4. Ohm’s Law Ohm’s law explains the relationship between voltage, amperage and resistance. Ohm’s law states that the flow of electricity through a conductor is directly proportional to the electromotive force that produces it. Expressed as an equation:
17. Ohm’s Law Example What is the voltage in a circuit with current of 6 amps and a resistance of 12 ?
18. Ohm’s Law Example Ohms law can also be used to teach electrical safety. What is the current flow in a circuit with a voltage of 120 volts and a resistance of 0.23 ? How does this teach electrical safety?
19. 5. Conductor Conductor: any material that has a low resistance to the flow of electricity. What type material makes a good conductor? Why? Is the resistance the same for all metals? Is the resistance of a conductor constant?
20. 6. Insulator What types of materials make good electrical insulators? How are the insulating qualities of a material rated? Is the resistivity of an electrical insulator constant? An insulator is any material that provides a high resistance to the flow of electricity.
21. 7. Electrical Circuit Electricity that leaves the source can pass through the switch, the light and return to the source. Is the illustration a circuit? Will the bulb be lit? An electrical circuit is a network of conductors and electrical components that form a complete path for electricity.
22. 8. Series Circuit This is a series circuit because an electron leaving the source must travel through the switch and both lights before it can return to the source. Can you give an example of this type of circuit? An Amp meter must be in series with the load to measure current (amps). In a series circuit the the electricity has no alternative paths from the source to the loads and back.
23. 9. Parallel circuit This is a parallel circuit because the electricity has alternative paths. Some will go through the blue light and some will go through the white light. Can you give an example of this type of circuit? A volt meter is attached parallel to the load to measure voltage. In parallel circuit the electricity has alternative paths.
24. 10. Alternating Current The amperage and voltage varies over time and periodically reverses direction (cycles). U.S. standard domestic electrical service is 60 cycle. Does current flow all the time?
25. 11. Direct Current-cont. Direct current The electrons move in one direction only. Amperage is constant. Voltage is constant The type of current used in batteries. Why isn’t AC current used in batteries?
26. 12. Electrical Power Electrical power is the rate at which electric energy is transferred in an electric circuit. The rate of energy transfer is measured in units of Watts. Watts are determine by multiplying the Voltage X the amperage. Which also means: Horsepower is the measure of mechanical power. Is there a conversion from Watts to horsepower?
27. 12. Electrical Power-cont. Electrical Power example Determine the power consumed by a resistor in a 12 volt system when the current is 2.1 amps. Electrical Power example Determine the amount of load a 1,500 W appliance will place on a circuit if it operates on 120 V..
28. 12. Electrical Power--Electrical wheel The electrical wheel Illustrates Ohm’s law and the electrical power equation. The value at the point of the 4 pie slices can be found using any one of the three equations on the rim of the pie slice. Example: E (Volts) can be determined by
29. 13. Electrical Energy Electrical energy is energy provided by the flow of electrons through an circuit. Electrical energy is measured in units of Watt-hours. What do the letters kWh on the face of the meter mean? What is the purpose of this type of meter?
30. 13. Electrical Energy-cont. Determine the amount of energy a 100 Watt light bulb will use when operated for 8 hours. What will it cost to operate the light bulb if the electrical energy costs 0.12 $/kWh? Online energy calculator http://www.csgnetwork.com/elecenergycalcs.html
31. 13. Electrical Energy-Electricity costs Watt-hour (Whr) is the measure of energy used. Used to determine energy cost. Domestic users the monthly cost is a combination of: monthly service charge kWh used x rate (kWh x $/kWh) taxes energy charge
32. 13. Electrical Energy—Electrical use rates Not all of the kWh’s used cost the same. Some utilities may contract for a base line use and charge more for electricity used above a baseline. Some large users may be able to negotiated a rate structure that reduces the cost per kWh as the amount used increases.
33. 13. Electrical Energy—Base line Structure Remember, monthly charges, energy costs, etc. will also be add to the monthly bill. Example of baseline structure. The user contracts 120 kWh per month for a rate of $0.12 kWr and 120% increase for any monthly use above 120 kWh. What is the bill for a month when 134 kWh’s were used?
34. 13. Electrical Energy—Tiered rates Determine the charge for 2500 kWh of electricity using the tiered rate structure. Example tiered electrical rates: First 500 kwh @ $0.07/kWh Next 1,000 kwh @ $0.065/kWh Over 1500 kWh @ $0.057/kWh
35. 13. Electrical Energy--Additional Factors Fuel charge Demand charges Off peak use Volunteer load cycling
36. 14. Resistance loads What are some examples of resistance loads? Resistance loads convert electrical energy to heat.
37. 15. Reactance loads Examples of reactance loads are motors and fluorescent lights. Reactance is the opposition of a circuit element to a change in the electrical current or voltage.
38. 16. Power Factor In some circuits the apparent load is the Watts (volts x amps), but due to energy stored in the load or non linear loads the real power will be less than apparent power. Power factor occurs in circuits with reactance loads. Power factor in a electrical system is the ratio of the real power flowing to the load compared to the apparent power in the circuit.
39. Power Factor—cont. Notice: the power, voltage and current curves are in phase--the peaks and lows are aligned vertically. In this situation the power factor is 1.0. In AC resistive circuits all of the power is consumed so none is stored in the load and no distortion occurs.
40. Power Factor - Reactive Loads Negative current means that for this portion of the cycle, power is flowing back to the source. During this part of the cycle, the actual power used is less than the indicated power use. The power factor is less than one (1). When the load is reactive the current lags the voltage. This causes a phase shift--the peaks and lows are not aligned vertically. Notice: during the time the instantaneous power curve is below zero, the current is negative.
41. Questions