COURSE TITLE: Fundamentals and Control of D.C. Generators and Motors

DUTY TITLE: Operation of D.C. Motors & Generators

DUTY NUMBER: 1800

TASK # 21 : Operation of a D.C. Generator

PURPOSE: To Understand the Concept, Control, and Troubleshooting Techniques of the Various Types of D.C. Generators.

TASKS:

1801 Demonstrate knowledge of basic direct current circuits.1802 Explain the theory of operation of a direct current motor.1803 Operate and test a direct current motor.1804 Operate and test a direct current shunt motor.1805 Perform calculations for horsepower, speed and torque for direct current motors.1806 Measure performance and efficiency of a direct current motor.

1807 Demonstrate knowledge of technical terms and units used in a basic direct current circuit.

1808 Demonstrate knowledge of the basic operations of variable speed control for direct current motors.

REVISION: 2016

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Schuylkill Technology Center-

South Campus15 Maple Avenue

Marlin, Pennsylvania 17951(570) 544-4748

RESIDENTIAL & INDUSTRIAL ELECTRICITY

NAME:

DATE:

DATE DUE:

ENGLISH LANGUAGE ARTSCC.1.2.11-12.J Acquire and use accurately general academic and domain-specific words and phrases, sufficient for reading, writing, speaking, and listening at the college and career readiness level; demonstrate independence in gathering vocabulary knowledge when considering a word or phrase important to comprehension or expressionCC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade level reading and content, choosing flexibly from a range of strategies and tools.

MATHCC.2.1.HS.F.4 Use units as a way to understand problems and to guide the solution of multi-step problems.CC.2.1.HS.F.6 Extend the knowledge of arithmetic operations and apply to complex numbers.

READING IN SCIENCE & TECHNOLOGYCC.3.5.11-12.B. Determine the central ideas or conclusions of a text; summarize complex concepts, processes, or information presented in a text by paraphrasing them in simpler but still accurate terms.CC.3.5.11-12.C. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.

WRITING IN SCIENCE & TECHNOLOGYCC.3.6.11-12.E. Use technology, including the Internet, to produce, publish, and update individual or shared writing products in response to ongoing feedback, including new arguments or information.

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*CORE CURRICULUM STANDARDS*

*ACADEMIC STANDARDS * READING, WRITING, SPEAKING & LISTENING

1.1.11.A Locate various texts, assigned for independent projects before reading.1.1.11.D Identify strategies that were most effective in learning1.1.11.E Establish a reading vocabulary by using new words1.1.11.F Understanding the meaning of, and apply key vocabulary across the various subject areas1.4.11.D Maintain a written record of activities1.6.11.A Listen to others, ask questions, and take notes

MATH2.2.11.A Develop and use computation concepts2.2.11.B Use estimation for problems that don’t need exact answers2.2.11.C Constructing and applying mathematical models2.2.11.D Describe and explain errors that may occur in estimates 2.2.11.E Recognize that the degree of precision need in calculating2.3.11.A Selecting and using the right units and tools to measure precise measurements2.5.11.A Using appropriate mathematical concepts for multi-step problems2.5.11.B Use symbols, terminology, mathematical rules, Etc.2.5.11.C Presenting mathematical procedures and results

SCIENCE3.1.12.A Apply concepts of systems, subsystems feedback and control to solve complex technological problems3.1.12.B Apply concepts of models as a method predict and understand science and technology3.1.12.C Assess and apply patterns in science and technology3.1.12D Analyze scale as a way of relating concepts and ideas to one another by some measure3.1.12.E Evaluate change in nature, physical systems and man-made systems3.2.12.A Evaluate the nature of scientific and technological knowledge3.2.12.B Evaluate experimental information for appropriateness3.2.12.C Apply elements of scientific inquiry to solve multi – step problems3.2.12.D Analyze the technological design process to solve problems3.4.12.A Apply concepts about the structure and properties of matter3.4.12.B Apply energy sources and conversions and their relationship to heat and temperature3.4.12.C Apply the principles of motion and force3.8.12.A Synthesize the interactions and constraints of science3.8.12.B Use of ingenuity and technological resources to solve specific societal needs and improve the quality of life3.8.12.C Evaluate the consequences and impacts of scientific and technological solutions

ECOLOGY STANDARDS4.2.10.A Explain that renewable and non-renewable resources supply energy and material.4.2.10.B Evaluate factors affecting availability of natural resources.4.2.10.C Analyze the use of renewable and non-renewable resources.4.2.12.B Analyze factors affecting the availability of renewable and non-renewable resources.4.3.10.A Describe environmental health issues.4.3.10.B Explain how multiple variables determine the effects of pollution on environmental health, natural processes and human practices.4.3.12.C Analyze the need for a healthy environment.4.8.12.A Explain how technology has influenced the sustainability of natural resources over time.

CAREER & EDUCATION13.1.11.A Relate careers to individual interest, abilities, and aptitudes13.2.11.E Demonstrate in the career acquisition process the essential knowledge needed13.3.11.A Evaluate personal attitudes that support career advancement

ASSESSMENT ANCHORSM11.A.3.1.1 Simplify expressions using the order of operationsM11.A.2.1.3 Use proportional relationships in problem solving settingsM11.A.1.2 Apply any number theory concepts to show relationships between real numbers in problem solving

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*ACADEMIC STANDARDS*

STUDENTThe student will be able to identify, connect and control the output of all three types of D.C. generators. (Series-Shunt-Compound)

TERMINAL PERFORMANCE OBJECTIVEGiven all the electrical tools and materials required, the student will be able to identify, connect and control the output of all three types of D.C. generators. (Series-Shunt-Compound)

SAFETY Always wear safety glasses when working in the shop. Always check with the instructor before turning power on. Always use tools in the correct manner. Keep work area clean and free of debris. Make sure guard is over motor couplings. Never wire a project without the correct wiring diagram.

RELATED INFORMATION1. Attend lecture by instructor.2. Obtain handout.3. Review chapters in textbook.4. Define vocabulary words.5. Complete all questions in this packet.6. Complete all projects in this packet.7. Complete K-W-L Literacy Assignment by Picking an Article From the

“Electrical Contractor” Magazine Located in the Theory Room. You can pick any article you feel is important to the electrical trade.

EQUIPMENT & SUPPLIES

1. Safety glasses 11. Various light bulbs

2. Hammer 12. Light fixture bank

3. Screw driver 13. Alligator clips

4. Awl 14. D.C. motor module

5. Wire strippers 15. D.C. generator

6. Side cutters 16. Prime mover (A.C. or D.C. motor)

7. Cable rippers 17. Couplings

8. Lineman pliers 18. Power supply

9. Needle nose pliers 19. THHN wire

10. Multi-meter 20. In line meters

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DC GeneratorsOUTLINE

What is a Generator?

Discuss magnetic induction with regard to generators. Explain how this induction process is affected with each 90° turn of the shaft.

Point out the armature and the fact that the voltage produced in the armature alternates polarity. Have students write down the rule about voltage produced in all rotating armatures, and the use of the commutator.

Referring to Figure 29-8 through Figure 29-16, explain how the commutator works. Also, be sure students gain a clear understanding of what the neutral plane is and why they need to be able to identify this position before setting the brushes. Explain rectified DC voltage and how it is achieved. Also, explain ripple pulsation and how it occurs.

Armature Windings

Lap-Wound Armatures

Have students put into their notes that lap wound armatures are used when low voltage and high current is required. Show some of these armatures while you discuss their construction and use.

Wave-Wound Armatures

Make sure students note that this type of armature is used when high voltage and low current are required. Compare the wave-wound armatures to the lap-wound armatures, as they are exactly opposite in construction and use.

Frog leg-Wound Armatures

Explain why these are the most commonly used, and have students compare them to the two previous armatures.

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Brushes

Explain how brushes are used, what they are made of, and how they are usually labeled.

Pole Pieces

Explain the role of the pole pieces in providing the magnetic field needed to operate the machine. Discuss their construction and have students explain why they are constructed of this material. Mention the magneto and explain how it differs from a regular DC generator.

Field Windings

Discuss series field and shunt windings, pointing out their differences in use, types of wire used, and resistance.

Explain when one would be better to use than the other.

Series Generators

Explain what a series generator is and how it works. Be sure students understand that the pole pieces need to have some residual magnetism. Discuss the three factors that determine the output voltage. Have students explain the effect of the wound wire on induction, increasing the lines of flux, and increased armature speed on the series generator.

Connecting Load to the Series Generator

Explain the effect of connecting a load to the series generator, emphasizing the continual strengthening of the magnetism of the pole pieces. Have students explain what this strengthening will result in, up to the point of pole saturation.

Give examples of where series generators are used, and why they are used in these instances instead of shunt generators.

Shunt Generators

Describe the shunt generator, displaying one as you do, and compare it to the series generator. Also, compare both types of shunt generators: self-excited and separately excited. Make sure students can point out the differences and explain why one would be better than the other under certain conditions. Give examples of where shunt generators

are used.

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Field Excitation Current

Explain what field excitation current is and how it controls the magnetic field, thus controlling the output voltage.

Explain what a shunt field rheostat is and how it is used. Also, discuss how the output voltage can be maintained at a constant rate with the use of a voltage regulator. Ask students if they know of a common use of a voltage regulator.

Generator Losses

Explain how voltage drop occurs in the shunt generator, and how the armature is involved in this loss process.

Make sure students note that because of the armature’s role in voltage drop, an armature with low- resistance is preferred for DC machines.

Discuss the other types of losses, how they occur, and types of corrective measures taken to cut these losses.

Compound Generators

Explain what a compound generator is, and then explain the two ways the series and shunt fields can be connected.

Display a compound generator for students to observe.

Compounding

Explain what compounding means. Discuss how a generator can become over-compounded, .at-compounded, or under-compounded.

Controlling Compounding

Explain why most DC machines start out at a state of being over-compounded, and how the shunt rheostat or series field diverter is used to reduce the amount of compounding.

Cumulative and Differential Compounding

Explain the two types of compounding and discuss why cumulative compounding is more widely used than differential compounding.

Counter torque

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Explain how counter torque is created by the opposing polarity of the armature and pole pieces. Be sure students note that counter torque is a measure of the useful electrical energy produced by the generator. Explain what dynamic braking or regenerative braking is and how it is used.

Armature Reaction

Explain what armature reaction is and how it is produced. Have students discuss why armature reaction is a problem.

Correcting Armature Reaction

Discuss the various ways that armature reaction can be corrected. Discuss the advantages and disadvantages of rotating the brushes and of inserting interpoles.

Setting the Neutral Plane

Using an AC voltmeter and a DC machine, explain and demonstrate how to determine the setting of the brushes and how to set them at the neutral plane. Let students practice doing this.

Paralleling Generators

Explain why more than one generator may be needed in a given situation, and how an equalizing connection is used. Discuss why the generators are hooked up in parallel, and have students explain why they aren’t hooked up in series. Discuss what could happen if an equalizing connection was not made. Demonstrate this set-up using two generators and an equalizing connection.

VocabularyCC.1.3.11-12.I Determine or clarify the meaning of unknown and multiple-meaning words and phrases based on grade

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level reading and content, choosing flexibly from a range of strategies and toolCC.3.5.11-12.D. Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 11–12 texts and topics.

Armature:

Armature reaction:

Brushes:

Commutator:

Compound generators:

Compounding:

Counter torque:

Cumulative compound:

Differential compound:

Field excitation current:

Frog leg wound armatures:

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Generator:

Lap-wound armatures:

Pole pieces:

Series field diverter:

Series field windings:

Series generator:

Shunt field windings:

Shunt generators:

Voltage regulation:

Wave-wound armatures:

Prime mover:

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Self excited:

Separately excited:

Polarity:

Fields:

End bells:

Interpoles:

REFERENCE PAGES

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D.C. GENERATORS

A variety of sources can supply mechanical energy to the DC generator to turn its armatures in order for its coils to cut through the lines of force in a magnetic field. These sources include steam, wind, a waterfall, or even an electric motor.

In a direct current generator, the commutator's job is to change the alternating current (AC), which flows into its armature, into direct current. To put it another way, commutators keep the current flowing in one direction instead of back and forth. They accomplish this task by keeping the polarity of the brushes stationed on the outside of the generator positive. The commutator is made up of copper segments, with a pair (of segments) for every armature coil being insulated from all the others.

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The stationary brushes, which are graphite connectors on the generator, form contact with opposite parts of the commutator. As the armature coil turns, it cuts across the magnetic field, and current is induced. At the first half turn of the armature coil (clockwise direction), the contacts between communicator and brushes are reversed. The first brush now contacts the opposite segment that it was touching during the first half turn, while the second brush contacts the segment opposite the one it touched during the first half turn. By doing this, the brushes keep current going on one direction, and deliver it to and from its destination.

When a DC generator contains only a single coil, it provides a pulsating dc output. Therefore, scientists use a number of coils to produce a more stable output.

Electric Motors and Generators, group of devices used to convert mechanical energy into electrical energy, or electrical energy into mechanical energy, by electromagnetic means. A machine that converts mechanical energy into electrical energy is called a generator, alternator, or dynamo, and a machine that converts electrical energy into mechanical energy is called a motor.

Two related physical principles underlie the operation of generators and motors. The first is the principle of electromagnetic induction discovered by the British scientist Michael Faraday in 1831. If a conductor is moved through a magnetic field, or if the strength of the magnetic field acting on a stationary conducting loop is made to vary, a current is set up or induced in the conductor. The converse of this principle is that of electromagnetic reaction, first observed by the French physicist André Marie Ampère in 1820. If a current is passed through a conductor located in a magnetic field, the field exerts a mechanical force on it.

The simplest of all dynamoelectric machines is the disk dynamo developed by Faraday. It consists of a copper disk mounted so that part of the disk, from the center to the edge, is between the poles of a horseshoe magnet. When the disk is rotated, a current is induced between the center of the disk and its edge by the action of the field of the magnet. The disk can be made to operate as a motor by applying a voltage between the edge of the disk and its center, causing the disk to rotate because of the force produced by magnetic reaction.

The magnetic field of a permanent magnet is strong enough to operate only a small practical dynamo or motor. As a result, for large machines, electromagnets are employed. Both motors and generators consist of two basic units, the field, which is the electromagnet with its coils, and the armature, the structure that supports the conductors which cut the magnetic field and carry the induced current in a generator or the exciting current in a motor. The armature is usually a laminated soft-iron core around which conducting wires are wound in coils.

If an armature revolves between two stationary field poles, the current in the armature moves in one direction during half of each revolution and in the other direction during the other half. To produce a steady flow of unidirectional, or direct, current from such a device, it is necessary to provide a means of reversing the current flow outside the generator once during each revolution. In older machines this reversal is accomplished by

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means of a commutator, a split metal ring mounted on the shaft of the armature. The two halves of the ring are insulated from each other and serve as the terminals of the armature coil. Fixed brushes of metal or carbon are held against the commutator as it revolves, connecting the coil electrically to external wires. As the armature turns, each brush is in contact alternately with the halves of the commutator, changing position at the moment when the current in the armature coil reverses its direction. Thus there is a flow of unidirectional current in the outside circuit to which the generator is connected. DC generators are usually operated at fairly low voltages to avoid the sparking between brushes and commutator that occurs at high voltage. The highest potential commonly developed by such generators is 1500 V. In some newer machines this reversal is accomplished using power electronic devices, for example, diode rectifiers.

Modern DC generators use drum armatures that usually consist of a large number of windings set in longitudinal slits in the armature core and connected to appropriate segments of a multiple commutator. In an armature having only one loop of wire, the current produced will rise and fall depending on the part of the magnetic field through which the loop is moving. A commutator of many segments used with a drum armature always connects the external circuit to one loop of wire moving through the high-intensity area of the field, and as a result the current delivered by the armature windings is virtually constant. Fields of modern generators are usually equipped with four or more electromagnetic poles to increase the size and strength of the magnetic field. Sometimes smaller interpoles are added to compensate for distortions in the magnetic flux of the field caused by the magnetic effect of the armature.

DC generators are commonly classified according to the method used to provide field current for energizing the field magnets. A series-wound generator has its field in series with the armature, and a shunt-wound generator has the field connected in parallel with the armature. Compound-wound generators have part of their fields in series and part in parallel. Both shunt-wound and compound-wound generators have the advantage of delivering comparatively constant voltage under varying electrical loads. The series-wound generator is used principally to supply a constant current at variable voltage. A magneto is a small DC generator with a permanent-magnet field.

In general, DC motors are similar to DC generators in construction. They may, in fact, be described as generators “run backwards.” When current is passed through the armature of a DC motor, a torque is generated by magnetic reaction, and the armature revolves. The action of the commutator and the connections of the field coils of motors are precisely the same as those used for generators. The revolution of the armature induces a voltage in the armature windings. This induced voltage is opposite in direction to the outside voltage applied to the armature, and hence is called back voltage or counter electromotive force (emf). As the motor rotates more rapidly, the back voltage rises until it is almost equal to the applied voltage. The current is then small, and the speed of the motor will remain constant as long as the motor is not under load and is performing no mechanical work except that required to turn the armature. Under load the armature turns more

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slowly, reducing the back voltage and permitting a larger current to flow in the armature. The motor is thus able to receive more electric power from the source supplying it and to do more mechanical work.

Because the speed of rotation controls the flow of current in the armature, special devices must be used for starting DC motors. When the armature is at rest, it has virtually no resistance, and if the normal working voltage is applied, a large current will flow, which may damage the commutator or the armature windings. The usual means of preventing such damage is the use of a starting resistance in series with the armature to lower the current until the motor begins to develop an adequate back voltage. As the motor picks up speed, the resistance is gradually reduced, either manually or automatically.

The speed at which a DC motor operates depends on the strength of the magnetic field acting on the armature, as well as on the armature current. The stronger the field, the slower is the rate of rotation needed to generate a back voltage large enough to counteract the applied voltage. For this reason the speed of DC motors can be controlled by varying the field current.

As stated above, a simple generator without a commutator will produce an electric current that alternates in direction as the armature revolves. Such alternating current is advantageous for electric power transmission, and hence most large electric generators are of the AC type. In its simplest form, an AC generator differs from a DC generator in only two particulars: the ends of its armature winding are brought out to solid unsegmented slip rings on the generator shaft instead of to commutators, and the field coils are energized by an external DC source rather than by the generator itself. Low-speed AC generators are built with as many as 100 poles, both to improve their efficiency and to attain more easily the frequency desired. Alternators driven by high-speed turbines, however, are often two-pole machines. The frequency of the current delivered by an AC generator is equal to half the product of the number of poles and the number of revolutions per second of the armature.

It is often desirable to generate as high a voltage as possible, and rotating armatures are not practical in such applications because of the possibility of sparking between brushes and slip rings and the danger of mechanical failures that might cause short circuits. Alternators are therefore constructed with a stationary armature within which revolves a rotor composed of a number of field magnets. The principle of operation is exactly the same as that of the AC generator described, except that the magnetic field (rather than the conductors of the armature) is in motion.

The current generated by the alternators described above rises to a peak, sinks to zero, drops to a negative peak, and rises again to zero a number of times each second, depending on the frequency for which the machine is designed. Such current is known as single-phase alternating current. If, however, the armature is composed of two windings, mounted at right angles to each other, and provided with separate external connections,

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two current waves will be produced, each of which will be at its maximum when the other is at zero. Such current is called two-phase alternating current. If three armature windings are set at 120° to each other, current will be produced in the form of a triple wave, known as three-phase alternating current. A larger number of phases may be obtained by increasing the number of windings in the armature, but in modern electrical-engineering practice three-phase alternating current is most commonly used, and the three-phase alternator is the dynamoelectric machine typically employed for the generation of electric power. Voltages as high as 13,200 are common in alternators.

MAINTENANCE INSTRUCTIONS

GENERAL INFORMATION:

When the field winding of a DC generator is connected in series with the armature, the generator is called a series-wound generator (Figure 10).The excitation current in a series-wound generator is the same as the current the generator delivers to the load. If the load has a high resistance and only draws a small amount of current, the excitation current is also small. Therefore, the magnetic field of the series field winding is weak, making the generated voltage low. Conversely, if the load draws a large current, the excitation current is also high. Therefore, the magnetic field of the series field winding is very strong, and the generated voltage is high.

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Figure 10 Series-Wound DC Generator

As you can see in Figure 11, in a series generator, changes in load current drastically affect the generator output voltage. A series generator has poor voltage regulation, and, as a result, series generators are not used for fluctuating loads. As is the case for the shunt-wound generator, a series-wound generator also exhibits some losses due to the resistance of the windings and armature reaction. These losses cause a lower terminal voltage than that for an ideal magnetization curve.

Figure 11 Output Voltage-vs.-Load Current for Series-Wound DC Generator

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GeneratorsA generator uses a magnet to get electrons moving.

There is a definite link between electricity and magnetism. If you allow electrons to move through a wire, they will create a magnetic field around the wire. Similarly, if you move a magnet near a wire, the magnetic field will cause electrons in the wire to move.

A generator is a simple device that moves a magnet near a wire to create a steady flow of electrons.

One simple way to think about a generator is to imagine it acting like a pump pushing water along. Instead of pushing water, however, a generator uses a magnet to push electrons along. This is a slight over-simplification, but it is nonetheless a very useful analogy.

There are two things that a water pump can do with water:

A water pump moves a certain number of water molecules. A water pump applies a certain amount of pressure to the water molecules.

In the same way, the magnet in a generator can:

push a certain number of electrons along apply a certain amount of "pressure" to the electrons

In an electrical circuit, the number of electrons that are moving is called the amperage or the current, and it is measured in amps. The "pressure" pushing the electrons along is called the voltage and is measured in volts. So you might hear someone say, "If you spin this generator at 1,000 rpm, it can produce 1 amp at 6 volts." One amp is the number of electrons moving (1 amp physically means that 6.24 x 1018 electrons move through a wire every second), and the voltage is the amount of pressure behind those electrons.

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The very first hydro-electric station ever built in the world was Niagara Falls. It was built by George Westinghouse using the visons of Nikola

Tesla.

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The Hoover Dam was the second hydro-electric station built. (There is that much concrete used in the construction of Hoover Dam, that

it is said it is not totally cured yet to this day)

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Nikola Tesla (left)George Westinghouse (Right)

A VOLTAGE IS INDUCED INTO THE WIRE AS IT CUTS LINES OF FORCE

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THE LOOP IS PARALLEL TO THE LINES OF FLUX; THERFORE NO CUTTING ACTION IS TAKING PLACE.

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THE COMMUTATOR IS USED TO CONVERT THE A.C. VOLTAGE PRODUCED IN THE ARMATURE TO D.C. VOLTS.

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The basic flow of voltage output as the coils rotates, cutting the lines of force produced by the magnetic fields.

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By adding more wires into the coils, the output becomes smoother and less “noisy” which means the collapsing of the magnetic fields will not be as much.

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1

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2

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THE LOOPS OF WIRE ARE WRAPPED AROUND SLOTS IN A METAL CORE MADE UP OF INDIVIDUAL LAMINATIONS

A D.C. MACHINE ARMATURE

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Commutator: Changes A.C. induced voltage to D.C. Voltage

POLE PIECES ARE MADE UP OF SOFT IRON AND PLACED INSIDE OF THE HOUSING CALLED A FIELD.

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SQUARE WIRE PERMITS MORE TURNS THAN ROUND WIRE IN THE SAME AREA

A SQUARE WIRE OF EQUAL SIZE CONTAINS MORE SURFACE AREA THAN A ROUND WIRE.

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BOTH SERIES AND SHUNT FIELD WINDINGS ARE LOCATED ON THE SAME POLE PIECE.

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BASIC FIELD ASSEMBLY CONSISTING OF 2 SHUNT FIELDS AND 1 INTERPOLE.

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SHUNT FIELD WINDINGS ARE CONNECTED IN PARALLEL WITH THE ARMATURE.

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SCHEMATIC DRAWING OF A SHUNT GENERATOR

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RESIDUAL MAGNETISM IN THE POLE PIECES PRODUCES AN INTIAL VOLTAGE WHICH CAUSES THE CURRENT TO FLOW THROUGH THE

SHUNT FIELD AND THE FIELD FLUX TO INCREASE.

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SEPERATELY EXCITED SHUNT GENERATORS MUST HAVE AN EXTERNAL POWER SOURCE TO PROVIDE EXCITATION CURRENT FOR

THE SHUNT FIELD.

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THE SHUNT FIELD RHEOSTAT IS USED TO CONTROL THE OUTPUT.

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THE VOLTAGE REGULATOR CONTROLS THE AMOUNT OF SHUNT FIELD CURRENT

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CHARACTERISTIC CURVES OF COMPOUND GENERATORS

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IN A CUMULATIVE-COMPOUND MACHINE, THE CURRENT FLOWS IN THE SAME DIRECTION IN BOTH THE SERIES AND SHUNT FIELD.

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A MAGNETIC FIELD IS PRODUCED AROUND THE ARMATURE.

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ARMATURE REACTION CHANGES THE POSITION OF THE NEUTRAL PLANE.

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INTERPOLES MUST HAVE THE SAME POLARITY AS THE MAIN FIELD THAT PRECEEDS IT.

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SETTING THE BRUSHES AT THE NEUTRAL PLANE

(The shunt field acts like a transformer and induces a voltage onto the armature. You install a meter onto the brush holders and take the reading to as close to zero as

possible)

NOTE: If the brushes are out of neutral plane, the speed will be affected as well as the brushes. There will be a lot of arcing at the brush contact point which in turn could damage the commutator.

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PROCEDURE

CC.2.1.HS.F.4 Use units as a way to understand problems and to guide the solution of multi-step problems.CC.3.5.11-12.C. Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks; analyze the specific results based on explanations in the text.1.6.11A Listen to others, ask questions, and take notes3.4.12.B Apply energy sources and conversions and their relationship to heat and temperature

EXPERIMENT # 1D.C. SERIES GENERATOR

PROCEDURE

1. Connect D.C. series generator to work station. (Diagram “A”)

2. Connect D.C. shunt motor to the generator (Prime mover).

3. Connect variable D.C. power supply to the motor so you can variate the speed of the prime mover.

4. Turn on power and notice that you can vary the speed of the motor by increasing or decreasing the D.C. power supply.

5. While the prime mover is at a low speed, measure and record the output of the generator.

6. Adjust the speed of the prime mover by 10 levels to the highest speed, and record all of the readings.

7. Install the light board on the generator and put a load of 1 light bulb on the generator. Repeat step # 6.

8. Now put a load of three light bulbs in parallel on the output of the generator and repeat step # 6.

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9. Make a graph to show the different readings and the different voltages. (Use a separate sheet of paper.) NEATNESS COUNTS!!!!

10. Why is there a difference between the one light bulb load and the three light bulb load?

11. What happened inside of the generator while these loads were applied? Describe how the lines of force affected the outcome.

12. Did the output voltage of the generator decrease when the loads were put on?

13. Explain why the output voltage decreases when the load was put on?

14. Now add as many light bulbs as you can until they do not light anymore. (The prime mover must be at a constant speed.)

15. Explain why this happened in step # 14?

16. Reverse the field with respect to the armature and repeat step # 14. (Diagram “B”) and explain why this happened.

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DIAGRAM “A” DIAGRAM “B

EXPERIMENT # 2 D.C. SHUNT GENERATOR

PROCEDURE

1. Connect the D.C. shunt generator in the self excited form. (Diagram “A”)

2. Connect a D.C. motor to the generator as the prime mover; the motor must be able to run at various speeds.

3. Connect the power supply to the prime mover.

4. Operate the motor at a low speed and take a no-load reading from the generator.

5. Increase the speed of the motor in ten steps and take readings from the generator. (This should be in a no load situation.)

6. Plot these findings on a graph and explain why the variations of no load voltages are different with the various speeds of the prime mover.

7. Install a load of three light bulbs on the generator, in parallel, and repeat step # 5. You must also take current readings as the speed of the prime mover increases.

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8. Reverse the field with respect to the armature. (Diagram “B”)

9. Repeat steps # 5 & # 6.

10. Explain what happens now that the field is reversed.

11. Now separately excite the field of the GENERATOR.

12. Set the prime mover at a constant speed (you can us an A.C. motor if you wish) and increase the excitation voltage to the generator in ten steps with no load on the generator.

13. Explain what happened and why.

14. Repeat steps #7 & #8 and explain your findings.

15. Next take ten voltage steps with the three light bulb load connected to the generator and plot a graph to show your increased output.

16. Did the prime mover “bogg” down or loose speed during any of these steps?

17. If so, explain why this happened.

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18. Next put as many light bulbs on the generator until it reaches saturation, is this point of saturation reached at the same load as in the series generator experiment?

19. Explain your results between these two experiments.

DIAGRAM “A” DIAGRAM “B” EXPERIMENT # 3

D.C. COMPOUND GENERATOR

PROCEDURE

1. Connect a D.C. generator in a compound, self excited manner. (Diagram “A”)

2. Connect a D.C. motor as the prime mover.

3. Connect the variable power supply to the prime mover.

4. Operate the motor at a low speed and take a no-load reading from the generator.

5. Increase the speed of the motor in ten steps and take readings from the generator. (This should be in a no load situation.)

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6. Plot these findings on a graph and explain why the variations of no load voltages are different with the various speeds of the prime mover.

7. Install a load of three light bulbs on the generator, in parallel, and repeat step # 5. You must also take current readings as the speed of the prime mover increases.

8. Reverse the field with respect to the armature. (Diagram “B”)

9. Repeat steps # 5 & # 6.

10. Explain what happens now that the field is reversed.

11. Now separately excite the field of the GENERATOR.

12. Set the prime mover at a constant speed (you can us an A.C. motor if you wish) and increase the excitation voltage to the generator in ten steps with no load on the generator.

13. Explain what happened and why.

14. Repeat steps #7 & #8 and explain your findings.

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15. Next take ten voltage steps with the three light bulb load connected to the generator and plot a graph to show your increased output.

16. Did the prime mover “bogg” down or loose speed during any of these steps?

17. If so, explain why this happened.

DIAGRAM “A” DIAGRAM “B”

ANSWER THE FOLLOWING QUESTIONS

1. Why does current go up when a load is applied to a generator?

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2. Name the three parts of a generator.

3. How can you test an armature, list two ways?

4. What are some ways to check a D.C. generator field?

5. Why does a series generator have little no load voltage?

6. Why does a shunt generator have higher no load voltage?

7. Explain why there are different characteristics when you change the direction of the fields in the compound and shunt generators?

8. What would happen if there was a short in a D.C. generator? (EXPLAIN!)

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WRITE A SUMMARY AND LIST THE DIFFERENCES IN THE THREE EXPERIMENTS YOU HAVE PERFORMED IN THIS PACKET.

(MUST BE ONE PAGE!!!!!)

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NAME: LEVEL: DATE:

CHECK LIST FOR D.C. GENERATOR PACKET

STEPS/TASKS MEETS NEEDS STANDARDS IMPROVEMENT

1) THE STUDENT COMPLETED ALL VOCABULARY TO 100% ACCURACY.2) THE STUDENT COMPLETED ALL WRITTEN WORK TO 100% ACCURACY.3) THE STUDENT COMPLETED THE WRITTEN ASSESSMENT TO 80% ACCURACY.4) THE STUDENT RECORDED ALL PROJECT RESULTS.5) THE STUDENT COMPLETED EXPERIEMENT # 16) THE STUDENT COMPLETED EXPERIEMENT # 27) THE STUDENT COMPLETED EXPERIEMENT # 38) THE STUDENT COMPLETED EXPERIEMENT # 19) THE STUDENT COMPLETED SUMMARY OF PROJECTS.

* ALL STEPS/TASKS MUST MEET THE STANDARDS IN ORDER TO ACHIEVE MASTERY.*

COMMENTS:

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INSTRUCTOR SIGNATURE: DATE:

NAME: DATE:

DC GENERATORS Post Test

Multiple ChoiceIdentify the letter of the choice that best completes the statement or answers the question.

____ 1. A device that converts mechanical input into DC electrical output is a(n)a. alternatorb. generatorc. motord. inverter

____ 2. The rotating part of a generator is called thea. statorb. fieldc. armatured. exciter

____ 3. The component of a DC generator that converts the armature AC into DC is thea. commutatorb. alternatorc. converterd. field

____ 4. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. The wind that provides low voltage and high current is the _____ wound.a. froglegb. lapc. wave

____ 5. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. The wind that provides high voltage and low current is the _____ wound.a. froglegb. lapc. wave

____ 6. Armatures are wound to provide high voltage, high current or some specific combination of voltage and current. The wind that provides moderate voltage and moderate current is the _____ wound.a. froglegb. lapc. wave

____ 7. The items that ride against the commutator to make electrical connection are thea. field windingsb. pole piecesc. armature windings

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d. brushes

____ 8. The magnetic field is sometimes provided by electromagnets. This is done by windings that are wound arounda. brushesb. pole piecesc. the armatured. the case

____ 9. Series field windings are connected in series with the armature. They are wound with _____ turns of fairly _____ wire.a. many, largeb. many, smallc. few, larged. few, small

____ 10. Shunt field windings are connected in parallel with the armature. They are wound with _____ turns of fairly _____ wire.a. many, largeb. few, largec. many, smalld. few, small

____ 11. The output voltage of the series generator is set when the load isa. connectedb. disconnected

____ 12. The output voltage of the shunt generator is set when the load isa. connectedb. disconnected

____ 13. The output voltage of a shunt generator is usually controlled by the amount ofa. field excitation currentb. input voltagec. input torqued. armature excitation current

____ 14. A generator containing both series and shunt field windings is called a _____ generator.a. self excitedb. separately excitedc. complexd. compound

____ 15. In a compound generator, the setting of the amount of currents in the series and shunt field windings determines thea. complexingb. compoundingc. excitingd. differential setting

____ 16. In a generator, the series field diverter is also called thea. series field shunt rheostatb. shunt field series rheostat

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c. series field exciterd. shunt field exciter

____ 17. A compound generator has both series and shunt field windings. When those windings are connected so they aid each other in the production of magnetism, that connection is called _____ compound.a. cumulativeb. differential

____ 18. A compound generator has both series and shunt field windings. When those windings are connected so their magnetic fields oppose, that connection is called _____ compound.a. cumulativeb. differential

CompletionComplete each sentence or statement.

19. Countertorque is caused by the magnetic attraction between the field poles and the _______________ magnetic field.

20. Armature reaction is the bending of the stator magnetic field by the _______________ magnetic field.

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Residential & Industrial ElectricityK-W-L WORKSHEET

NAME: LEVEL: DATE:

ARTICLE TITLE:

TIME START: TIME FINISH:

K What do I already KNOW about this topic?

W What do I WANT to know about this topic?

L What did I LEARN after reading ABOUT this topic?

I checked the following before reading: Headlines and Subheadings Italic, Bold, and Underlined words Pictures, Tables, and Graphs Questions or other key information

I made predictions AFTER previewing the article.

Comments:

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Instructor Signature:

Instructional Aide Signature:

NAME: DATE:

DC GENERATORS Pre Test

Multiple ChoiceIdentify the letter of the choice that best completes the statement or answers the question.

____ 1. A device that converts mechanical input into DC electrical output is a(n)a. alternatorb. generatorc. motord. inverter

____ 2. The rotating part of a generator is called thea. statorb. fieldc. armatured. exciter

____ 3. The component of a DC generator that converts the armature AC into DC is thea. commutatorb. alternatorc. converterd. field

____ 4. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. The wind that provides low voltage and high current is the _____ wound.a. froglegb. lapc. wave

____ 5. Armatures are wound to provide high voltage, high current, or some specific combination of voltage and current. The wind that provides high voltage and low current is the _____ wound.a. froglegb. lapc. wave

____ 6. Armatures are wound to provide high voltage, high current or some specific combination of voltage and current. The wind that provides moderate voltage and moderate current is the _____ wound.a. froglegb. lapc. wave

____ 7. The items that ride against the commutator to make electrical connection are the

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a. field windingsb. pole piecesc. armature windingsd. brushes

____ 8. The magnetic field is sometimes provided by electromagnets. This is done by windings that are wound arounda. brushesb. pole piecesc. the armatured. the case

____ 9. Series field windings are connected in series with the armature. They are wound with _____ turns of fairly _____ wire.a. many, largeb. many, smallc. few, larged. few, small

____ 10. Shunt field windings are connected in parallel with the armature. They are wound with _____ turns of fairly _____ wire.a. many, largeb. few, largec. many, smalld. few, small

____ 11. The output voltage of the series generator is set when the load isa. connectedb. disconnected

____ 12. The output voltage of the shunt generator is set when the load isa. connectedb. disconnected

____ 13. The output voltage of a shunt generator is usually controlled by the amount ofa. field excitation currentb. input voltagec. input torqued. armature excitation current

____ 14. A generator containing both series and shunt field windings is called a _____ generator.a. self excitedb. separately excitedc. complexd. compound

____ 15. In a compound generator, the setting of the amount of currents in the series and shunt field windings determines thea. complexingb. compoundingc. excitingd. differential setting

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____ 16. In a generator, the series field diverter is also called thea. series field shunt rheostatb. shunt field series rheostatc. series field exciterd. shunt field exciter

____ 17. A compound generator has both series and shunt field windings. When those windings are connected so they aid each other in the production of magnetism, that connection is called _____ compound.a. cumulativeb. differential

____ 18. A compound generator has both series and shunt field windings. When those windings are connected so their magnetic fields oppose, that connection is called _____ compound.a. cumulativeb. differential

CompletionComplete each sentence or statement.

19. Countertorque is caused by the magnetic attraction between the field poles and the _______________ magnetic field.

20. Armature reaction is the bending of the stator magnetic field by the _______________ magnetic field.

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