MODULE 4: ELECTRICAL SYSTEMS Engineering Mathematics.

MODULE 4: ELECTRICAL SYSTEMS

Engineering Mathematics

Copyright © Texas Education Agency 2012. All rights reserved.

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Introduction

The Electrical Systems lesson will cover electricity, Ohm’s Law, measuring, and efficiency. You will determine a 6-volt battery current, voltage, and resistance.

Student teams will perform an energy audit of their school.

In addition, you will design a building/wing/floor that meets a certain power consumption criteria, using conventional power sources (fossil fuels) and renewable power sources.


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Chapter 4: Outline

1. Ohm’s Law, Power and DC2. Serial vs. Parallel, Capacitors,

and Inductors3. AC Circuits4. Transformers and Motors


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Objectives and Results

Students will understand the meaning of electricity, Ohm’s Law, and the meaning of electrical systems.

Students will understand the different types of electrical systems, as well as the careers and educational opportunities available in the electrical systems industry.

Student teams will perform an energy audit of their school and design a building/wing/floor that meets a certain power consumption criteria, using conventional power sources (fossil fuels) and renewable power sources.


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Schedule of Assignments

Class/Week Topic Reading Assignment

1-2 • Introduction• Vocabulary• Electrical Engineering O*Net

Chapter 4.1 #1-Individual Write a one-page paper about the Electrical Engineering Occupation.

3-10 • Ohm’s Law Chapter 4.2, 4.3 #2 In teams of 2-3, complete the Ohm’s Law Exercise.

11-20 • Energy Audit Chapter 4.4 #3 In teams of 2-3, complete the Electrical Systems Project (Energy Audit).


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Vocabulary

Electrical Systems Ohm’s Law Motor Electrical Power Efficiency


Electrical Engineering

There are several career opportunities in the electrical systems field.

Electrical engineering is the branch of engineering that deals with the technology of electricity, especially the design and application of circuitry and equipment for power generation and distribution, machine control, and communications.

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Careers/Educational Opportunities

Career and educational opportunities choices include the following: Electrical engineers Electrical engineering technicians Electrical engineering technologists Electricians Electrical and electronic equipment

assemblers Electronics engineering technologists

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Electrical Engineering Assignment Visit the O*Net website (

www.onetonline.org).

Write a one-page essay on the electrical engineering profession.

Discuss at least one sub-specialty of electrical engineering in your essay.

Use the O*Net website and at least one other primary source.

http://www.onetonline.org/


Electrical Systems

The electrical systems lesson consists of seven sections:

What is Electricity? What is Ohm’s Law? What are Electrical Systems? Types of Electrical Systems Careers and Educational Opportunities Ohm’s Law Exercise Electrical Systems Project

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What is Electricity?

Electricity was not 'invented.” Its characteristics and uses have been known about and developed over hundreds of years.

Electricity is a form of energy involving the flow of electrons.

All matter is made up of atoms, and an atom has a center, called a nucleus.

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What is Electricity?, cont.

The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons.

The negative charge of an electron is equal to the positive charge of a proton, and the number of electrons in an atom is usually equal to the number of protons.

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Electric Current

When the balancing force between protons and electrons is upset by an outside force, an atom may gain or lose an electron.

When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current.

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What is Ohm’s Law?14

When a voltage is applied to a circuit containing only resistive elements (i.e., no coils), current flows according to Ohm's Law, which is shown below.


What is Ohm’s Law?, cont.15

WhereI = Electrical Current (amperes),V = Voltage (volts), and R = Resistance (ohms).Ohm’s Law is used to determine the electric current in electrical systems.


What is Ohm’s Law?, cont.16

Therefore, if the voltage is increased, the current will increase provided the resistance of the circuit does not change.

Similarly, increasing the resistance of the circuit will lower the current flow, if the voltage is not changed.

The formula can be reorganized so that the relationship can easily be seen for all of the three variables.


What are Electrical Systems? Electrical systems are utilities that

provide electricity. They are groups of electrical components

connected to carry out some operation. For example, an electrical system may

be equipment in a motor vehicle that provides electricity to start the engine and ignite the fuel and operate the lights and windshield wiper and heater and air conditioner and radio.

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Electric Motors

Electric motors involve rotating coils of wire which are driven by the magnetic force exerted by a magnetic field on an electric current.

They transform electrical energy into mechanical energy.

There are two types of motors: DC and AC.

The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.

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DC and AC Motors19


DC Motors A DC motor is an electric motor that

runs on direct current (DC) electricity. In direct current (DC, also dc), the flow of

electric charge is only in one direction. DC motors are used to run machinery,

often eliminating the need for a local steam engine or internal combustion engine.

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DC Motors, cont. DC motors can operate directly from

rechargeable batteries, providing the motive power for the first electric vehicles.

Today, DC motors are still found in applications as small as toys and disk drives or in large sizes to operate steel rolling mills and paper machines.

Modern DC motors are nearly always operated in conjunction with power electronic devices.

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DC Motor Operation22


AC Motor

An AC motor is an electric motor that is driven by an alternating current.

In alternating current (AC, also ac), the movement of electric charge periodically reverses direction.

In direct current (DC, also dc), the flow of electric charge is only in one direction.

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AC Power

AC is the form in which electric power is delivered to businesses and residences.

The usual waveform of an AC power circuit is a sine wave.

An electric motor that operates on alternating current, like the kind of power source found in a household outlet.

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AC Motor Operation25


Ohm’s Law Exercise

In this practice exercise, you will build a one-battery, one-resistor circuit.

You will use Ohm’s Law to calculate the power and measure efficiency.

You will learn to use the following items: Voltmeter

Ammeter

Ohmmeter

Ohm's Law

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Project Team Protocol

Form teams of 2-3 students. Random selection Teacher choice Student choice

Student teams will complete the team contract spreadsheet and assign roles with their teams.

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Materials: Ohm’s Law ExerciseThe team’s materials lead will gather the parts and materials listed below: Calculator (or pencil and paper

for doing arithmetic) 6-volt battery Assortment of resistors

between 1kΩ and 100kΩ in value

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Procedures: Ohm’s Law Exercise

The resistance values are between 1 kΩ and 100 kΩ for the sake of obtaining accurate voltage and current readings with your meter.

With very low resistance values, the internal resistance of the ammeter has a significant impact on measurement accuracy.

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Procedures: Ohm’s Law Exercise, cont.

Very high resistance values can cause problems for voltage measurement, the internal resistance of the voltmeter substantially changing circuit resistance when it is connected in parallel with a high-value resistor.

At the recommended resistance values, there will still be a small amount of measurement error due to the "impact" of the meter, but not enough to cause serious disagreement with calculated values.

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Ohm’s Law Exercise

SCHEMATIC DIAGRAM

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Procedures: Ohm’s Law Exercise

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Instructions: Ohm’s Law Exercise

1. Select a resistor from the assortment, and measure its resistance with your multimeter set to the appropriate resistance range.

2. Be sure not to hold the resistor terminals when measuring resistance or else your hand-to-hand body resistance will influence the measurement!

3. Record this resistance value for future use.

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Instructions: Ohm’s Law Exercise, cont.

4. Build a one-battery, one-resistor circuit. A terminal strip is shown in the illustration, but any form of circuit construction is okay.

5. Set your multimeter to the appropriate voltage range and measure voltage across the resistor as it is being powered by the battery.

6. Record this voltage value along with the resistance value previously measured.

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7. Set your multimeter to the highest current range available. Break the circuit and connect the ammeter within that break, so it becomes a part of the circuit, in series with the battery and resistor.

8. Select the best current range: whichever one gives the strongest meter indication without over-ranging the meter. If your multimeter is auto-ranging, of course, you need not bother with setting ranges.

9. Record this current value along with the resistance and voltage values previously recorded.

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10.Taking the measured figures for voltage and resistance, use the Ohm's Law equation to calculate circuit current. Compare this calculated figure with the measured figure for circuit current:

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11.Taking the measured figures for voltage and current, use the Ohm's Law equation to calculate circuit resistance. Compare this calculated figure with the measured figure for circuit resistance:

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12.Finally, taking the measured figures for resistance and current, use the Ohm's Law equation to calculate circuit voltage. Compare this calculated figure with the measured figure for circuit voltage:

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V = I x R



13.There should be close agreement between all measured and all calculated figures. Any differences in respective quantities of voltage, current, or resistance are most likely due to meter inaccuracies. These differences should be rather small, no more than several percent. Some meters, of course, are more accurate than others!

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14.Substitute different resistors in the circuit and re-take all resistance, voltage, and current measurements. Re-calculate these figures and check for agreement with the experimental data (measured quantities). Also note the simple mathematical relationship between changes in resistor value and changes in circuit current. Voltage should remain approximately the same for any resistor size inserted into the circuit, because it is the nature of a battery to maintain voltage at a constant level.

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Electrical Systems Project

Design Challenge Student teams will perform an energy

audit of their school. In addition, you will design a

building/wing/floor that meets a certain power consumption criteria, using conventional power sources (fossil fuels) and renewable power sources.

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Credits42

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MODULE 4: ELECTRICAL SYSTEMS Engineering Mathematics.

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