Seminar

Seminar Report on Homopolar GeneratorINTRODUCTION 2011-12 A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. A potential difference is created between the center of the disc and the rim (or ends of the cylinder), the electrical polarity depending on the direction of rotation and the orientation of the field. It is also known as a unipolar generator, acyclic generator, disk dynamo, or Faraday disc. The voltage is typically low, on the order of a few volts in the case of small demonstration models, but large research generators can produce hundreds of volts, and some systems have multiple generators in series to produce an even larger voltage.[1] They are unusual in that they can source tremendous electric current, some more than a million amperes, because the homopolar generator can be made to have very low internal resistance. Dept.of Electrical & Electronics Engg. G.P.T.C, Muttom -1- Seminar Report on Homopolar Generator 2011-12 FARADAY DISC THE FIRST HOMOPOLAR GENRATOR Faraday developed a generator consisting of a disk magnet coaxial to a conductive disk similar to the diagram shown in Figure 1-L This generator is called a Homopolar generator because it only uses one pole of the magnet. There are 4 modes of operation of the Homopolar Generator (HPG): the results of which comprise what is known as Faraday's Final Riddle: Does a magnetic field move with the magnet. The generator in Figure 1-1 is comprised of a disk magnet attached to a motor (A) and a conductive copper disk attached to motor (B). The disks are placed next to each other to allow them to rotate coaxial to each other. A stationary galvanometer is connected between the edge of the conductive disk and the shaft of motor B with brush contacts. The Galvanometer enables the operator to detect radial current generated in the disk (An indication that power is being generated). There are four modes of operation of the Homopolar generator. Some of the modes of operation are not discussed in text books since there is no accepted explanation for the seemingly paradoxical behavior of the HPG. In the following descriptions, the disk magnet is referred to as the magnet and the conductive copper disk is referred to as the disk. Dept.of Electrical & Electronics Engg. G.P.T.C, Muttom -2- P. In the third mode of operation. In this mode. the magnet is stationary and the disk is rotated by motor B. A normal reaction is to conclude that power is generated when there is relative motion between the disk and the magnet. however. One might try to predict that power should be generated since there is relative motion between the disk and the magnet (such as in mode 2). no power is detected. the magnet is rotated by motor A and the disk is stationary. G.C. In this mode of operation. Dept. Muttom -3- .Seminar Report on Homopolar Generator 2011-12 In the first mode of operation.of Electrical & Electronics Engg. power is generated. the galvanometer detects power generated in the disk. both the magnet and the disk are rotated together. In the second mode of operation. the Galvanometer does not detect the flow of current and thus we conclude that there is no power generated in the disk. In the fourth mode of operation. both the disk and the magnet are stationary.T. Again one may conclude that since there is no relative motion between the disk and the magnet (such as in mode 1) that there should be no power generated: however. Nikola Tesla was interested in the Faraday disc and conducted work with homopolar generators. patents were awarded to C. Later. was in Dept. De Ferranti and C. U. The Forbes dynamo.516. This would have greatly reduced the frictional losses caused by sliding contacts by allowing both electrical pickups to interface with the shafts of the two disks rather than at the shaft and a high-speed rim.of Electrical & Electronics Engg.[2] He eventually patented an improved version of the device and his US patent ("Dynamo Electric Machine") describes an arrangement of two parallel discs with separate. Thomson for their work with homopolar generators. Each disc had a field that was the opposite of the other. P.S.T. F. so that the flow of current was from the one shaft to the disc edge. Z. Other early patents for homopolar generators were awarded to S. Steinmetz and E.P. developed by the Scottish electrical engineer George Forbes. a modified version combining the magnet and disc in a single rotating part (the rotor) was developed. G. Muttom -4- . parallel shafts. Delafield. joined like pulleys by a metallic belt. Patent 278. Sometimes the name homopolar generator is reserved for this configuration.Seminar Report on Homopolar Generator 2011-12 HOMOPOLAR GENERATOR DEVELOPMENT Long after the original Faraday disc had been abandoned as a practical generator. Batchelor separately. One of the earliest patents on the general type of homopolar generators was attained by A.C. across the belt to the other disc edge and to the second shaft. G. These devices used heavy disks as a form of flywheel to store mechanical energy that could be quickly dumped into an experimental apparatus.of Electrical & Electronics Engg. Australian National University.Seminar Report on Homopolar Generator 2011-12 widespread use during the beginning of the 20th century. Much of the development done in homopolar generators was patented by J. An early example of this sort of device was built by Sir Mark Oliphant at the Research School of Physical Sciences and Engineering. E. Industrial designs of 10 MJ were introduced for a variety of roles. It stored up to 500 megajoules of energy and was used as an extremely high-current source for synchrotron experimentation from 1962 until it was disassembled in 1986. Dept. Eickemeyer. Homopolar generators underwent a renaissance in the 1950s as a source of pulsed power storage. Noeggerath and R.P.C. including electrical welding. from powering railguns to linear motors (for space launches) to a variety of weapons designs. Similar devices of even larger size are designed and built by Parker Kinetic Designs (formerly OIME Research & Development) of Austin. Muttom -5- . They have produced devices for a variety of roles.T. Oliphant's construction was capable of supplying currents of up to 2 megaamperes (MA). Seminar Report on Homopolar Generator 2011-12 DESCRIPTION AND OPERATION Disk-type generator Basic Faraday disc generator This device consists of a conducting flywheel rotating in a magnetic field with one electrical contact near the axis and the other near the periphery.T. the output voltage never changes polarity.of Electrical & Electronics Engg. so the electromotive force is radial. the angular momentum of the rotor is used to store energy over a long period and then release it in a short time.C.P. Muttom -6- . which results in large losses at the low voltages generated. It has been used for generating very high currents at low voltages in applications such as welding. The charge separation results from the Lorentz force on the free charges in the disk. The electrical contacts are usually made through a "brush" or slip ring. The motion is azimuthal and the field is axial. Some of these losses can be reduced by using mercury Dept. G. electrolysis and railgun research. In pulsed energy applications. In contrast to other types of generators. If the magnetic field is provided by a permanent magnet.C. Before the discovery of the electron and the Lorentz force law. NaK) as the "brush". G. the phenomenon was inexplicable and was known as the Faraday paradox. the generator works regardless of whether the magnet is fixed to the stator or rotates with the disc.of Electrical & Electronics Engg. Dept.T.P.Seminar Report on Homopolar Generator 2011-12 or other easily liquified metal or alloy (gallium. Muttom -7- . to provide essentially uninterrupted electrical contact. Hannes Alfvén and Carl-Gunne Fälthammar write: "Since cosmical clouds of ionized gas are generally magnetized. Muttom -8- .Seminar Report on Homopolar Generator DRUM-TYPE GENERATOR 2011-12 A drum-type homopolar generator has a magnetic field (B) that radiates radially from the center of the drum and induces voltage (V) down the length of the drum. G.P.T. Astrophysical unipolar inductors Unipolar inductors occur in astrophysics where a conductor rotates through a magnetic field. their motion produces induced electric fields For example the motion of the magnetized interplanetary plasma produces electric fields that are essential for the production of aurora and magnetic storms" ". A conducting drum spun from above in the field of a "loudspeaker" type of magnet that has one pole in the center of the drum and the other pole surrounding the drum could use conducting ball bearings at the top and bottom of the drum to pick up the generated current. the rotation of a conductor in a magnetic field produces an electric field in the system at rest. for example. Cosmical Electrodynamics. In their book. This phenomenon is well known from laboratory experiments and is usually called 'homopolar ' or 'unipolar' induction. the movement of the highly conductive plasma in a cosmic body's ionosphere through its magnetic field. Dept.of Electrical & Electronics Engg.C.. C. states that the force on an electron is proportional to the cross product of its velocity and the magnetic flux vector. This law (in its modern form) states that an electric current is induced in a closed electrical circuit when the magnetic flux enclosed by the circuit changes (in either magnitude or direction). discovered thirty years after Faraday's death. This law. the Moon. the Solar Wind. this means that the force is at right-angles to both the velocity (azimuthal) and the magnetic flux (axial).Seminar Report on Homopolar Generator 2011-12 Unipolar inductors have been associated with the aurorae on Uranus binary stars. however. Physics Like all dynamos.T. black holes. For the Faraday disk it is necessary. The Lorentz force law is more easily used to explain the machine's behaviour. to consider that the circuit(s) consist of each radial "spoke" of the disk connected to the rim and center and then through the external circuit. galaxies. The radial movement of the electrons in the disc produces a charge separation between the center of the Dept. In geometrical terms. G. the Faraday disc converts kinetic energy to electrical energy.P. which is therefore in a radial direction. the Jupiter Io system.of Electrical & Electronics Engg. sunspots. This machine can be analysed using Faraday's own law of electromagnetic induction. Muttom -9- . and in the Venusian magnetic tail. The motion is azimuthal and the field is axial. The charge separation results from the Lorentz force on the free charges in the disk. Muttom . electrolysis and railgun research.10 G.Seminar Report on Homopolar Generator 2011-12 disc and its rim. the output voltage never changes polarity. It has been used for generating very high currents at low voltages in applications such as welding. Disk-type generator Basic Faraday disc generator This device consists of a conducting flywheel rotating in a magnetic field with one electrical contact near the axis and the other near the periphery.of Electrical & Electronics Engg. so the electromotive force is radial.C. The electrical contacts are usually made Dept. In pulsed energy applications. and if the circuit is completed an electric current will be produced. . In contrast to other types of generators. the angular momentum of the rotor is used to store energy over a long period and then release it in a short time.T.P. Some of these losses can be reduced by using mercury or other easily liquified metal or alloy (gallium. If the magnetic field is provided by a permanent magnet. the generator works regardless of whether the magnet is fixed to the stator or rotates with the disc. which results in large losses at the low voltages generated. Before the discovery of the electron and the Lorentz force law.11 - . NaK) as the "brush".T. Dept. to provide essentially uninterrupted electrical contact.P. Muttom . the phenomenon was inexplicable and was known as the Faraday paradox. G.of Electrical & Electronics Engg.C.Seminar Report on Homopolar Generator 2011-12 through a "brush" or slip ring. T. The general idea was that an HPG might lack back-torque if the rotor and stator circuits are radially symmetrical. perhaps here is a device which accomplishes the feat. If a pair of these was hooked together in motor/generator configuration. If all wires were replaced with cups and tubes. Tewari and Depalma in fringe-science publications claim to have observed anomalous behavior when investigating these devices. Yet a radially-symmetric HPG does not change flux linkage when rotating.12 - . ("HPGs" or "N-machines".of Electrical & Electronics Engg. If there is a way to extract the energy of the quantum vacuum sea. Muttom . yet it would require little driving energy. Dept. Impossible by standard physics. Yet it does. The generator would create large currents and heat output.P. and drew some GIFs of possible devices.C. conservation of energy would be violated. Check out the above links for these diagrams. they might self-accelerate anomalously and spin without extrnal energy input. G.Seminar Report on Homopolar Generator EXPERIMENT 2011-12 In 1992-94 I messed around with homopolar generators. of course. would the mechanical energy per output wattage be reduced? If this were true.) tried a simple test. and so it might not be expected to produce output currents. since the oxide crust on the mercury contributed a large friction compared to the EM braking effects. Muttom . I only relied on twisting up the thread and making crude time measurements of the unwinding. and see if unexplained excess heat is evolved. To detect forces.13 - . Hint for anyone who wants to try the experiment: silver-plate the copper so that the mercury will wet it.Seminar Report on Homopolar Generator 2011-12 The pipecaps/mercury experiment was my crude attempt to detect changes in electromagnetic braking in a shorted. symmetrical HPG. Unfortunately my setup didn't show low friction without the magnet. Later I realized that the crust could be eliminated.C. The crust/scum on the mercury gave such high friction that I couldn't see any obvious difference between the magnet version and the no-magnet version. This will vastly lower the friction and make the differences between the magnet version and the no-magnet version measurable.P. Big hint: build a large.T. (See if the shorted homopolar generator makes more heat energy than is input by the wires to the driving motor. stick it in a calorimiter.) Dept. spin it with a motor. heavy version of one of these shorted-out generators. I hoped to compare the braking forces with and without the permanent magnet present. and put light oil on the mercury to seal it from oxygen and prevent the formation of an oxide scum layer.of Electrical & Electronics Engg. G. This experiment needs to be repeated. Liquid metal brushes would be better.T. Perhaps it will help to clarify things.P. G. I have come up with some observations and questions. When a magnetic field is applied (vertical field in fig 1b) and the two halves are spun together as a unit. The diagram below depicts a simplified Homopolar Generator (HPG).C.of Electrical & Electronics Engg." of a classic HPG. while the other half acts as the "external circuit. Are you confused about spinning magnets versus spinning disks? Here's more to think about. Muttom .14 - .Seminar Report on Homopolar Generator 2011-12 In thinking long and hard about HPGs." Carbon brushes connect the halves with sliding contact. Rather than using a separate external circuit and a spinning disk. I've combined them into a two-disk arrangement. One half of the device in fig 1a is the "disk. the relative motion of the metal and the magnetic field should cause a Dept. The two halves are placed together in fig 1b. It is large if one half spins and the other is kept still. the polarity of the radial voltage and the radial separation of charges should be opposite in each disk.15 - . again with a voltage only. and therefor should create no relative voltage between the halves. should result in equal voltages radially across both halves. Muttom . the positive and negative regions are in electrical contact and a very large electric current should appear.T. so rotating magnets should create no current. However. if the metal assembly is held still and the magnets are spun instead.P.of Electrical & Electronics Engg. Since the two halves are in sliding contact. In other words. This current is zero if the two halves are spun together. which causes the rim of the metal assembly to aquire a positive charge. If the upper and lower halves of the device are spun in opposite directions. and the axis of the assembly to receive an equal negative charge. There is a momentary separation of charge. or the magnetic field. It is twice as large if both halves are spun in opposite directions. any relative rotation of the MAGNET. Fig 1c shows my idea of how HPGs are able to create electric currents. G. instead the device acts like a charged capacitor as long as the rotation continues. the same radial voltage should appear and the same separation of charges should exist on the object.Seminar Report on Homopolar Generator 2011-12 radial voltage to appear. but no constant current. Also.C. NO CURRENT RESULTS. the magnetic field might spin with the magnet or it Dept. but this cannot be detected by the HPG disks. In reality. You'll end up with the "classic" HPG circuit in full.16 - . you create a "classic" HPG having a spinning disk and a nonspinning "external circuit. but need not apply any forces against the permanent magnet. Instead. it only cares about differing rotation of the two metal parts.Seminar Report on Homopolar Generator 2011-12 might not. If you hold one half of the metal parts still and spin the other half. while rotation of his bar magnet does not. The HPG doesn't care if the magnet spins. the only important motion is the *relative* movement between Faraday's disk and his external circuit. You can even carve away most of the shell of the non-spinning half and form it into "wires"." Simply add a current meter in series with the shaft of the nonspinning half depicted above. G. It explains the seeming non-reversibility of current-generating action in Faraday's homopolar experiment. Muttom .of Electrical & Electronics Engg.T. This then shows why the rotating copper parts might apply backaction forces against the external circuit. It APPEARS that there is a paradox. and the rotation of the magnet is unimportant.C.P. and that the rotation of Faraday's disk generates current. Of course the presence of the magnetic field is necessary to accomplish the effect and Dept. There is a chance that the device of fig. In this case a motor could be used to spin one disk. Muttom . but its rotation relative to the average rotation of the diskplus-circuit assembly only creates a net radial charge separation without creating constant current. 1c will not create back-action against whatever mechanical forces are causing it to turn. the homopolar generator is not as weird as it first seems. and that there is a true anomaly here.of Electrical & Electronics Engg. Note that these are all UNTRIED THOUGHT EXPERIMENTS.17 - . If the mechanical energy input to a homopolar generator is not in perfect 1:1 proportion to its heat output. G.T. Once we realize that the external circuit is the "stator" of the device.C. then there are mysteries here to be investigated.P. and so Dept. but the current would not create electromagnetic back action.Seminar Report on Homopolar Generator 2011-12 create current. and the current in them would create heat. There is a small chance that the HPG does not work as I describe above. of Electrical & Electronics Engg. since charge is conserved. I'll leave you with this though. It seems as though there is an imbalanced charge along the rim of the magnet. an explosive runaway flywheel reaction. resulting in heat energy "from nowhere. it is hanging in space along the axis of rotation! (At least my crude drawing strongly suggests this. Am I mistaken?) Dept.C. which would in turn spin the disks even faster. until it shatters from the radial forces? There are rumors that such things happen. The equal and opposite charge is not on the magnet at all. Muttom . the generated current in the disks might even create a motor action which would spin the disks. and again create "energy from nowhere. I have attempted to sketch the electrostatic field created by a spinning disk magnet. G. which would create higher current but no back-action force." Or as with the Searle device claims." If you short out a radially constructed HPG and spin it fast enough. However. and which would create continuous acceleration.18 - . In the diagram below.T.P. will it start spinning faster and faster.Seminar Report on Homopolar Generator 2011-12 the motor would do no work in driving the disks. a region of opposite charge must appear elsewhere. I haven't heard that anyone has tried this recently and verified that nothing mysterious occurs. . and Dept. since the field lines seem to end in empty space at the axis of rotation. If there were a cloud of charged particles surrounding this spinning magnet.of Electrical & Electronics Engg. EM does not apply correctly when the objects in question are rotating. G.C. Is this true? I don't know how to think about this.T.P. I've heard that in Gen.Seminar Report on Homopolar Generator 2011-12 Is this real? Isn't it like those strange circular e-fields which exist in the empty space around a toroidial AC inductor? But this is the DC version. And I cannot see how the e-field could have these closed loops. would the rotating field cause them to collect at the axis? Surely simple electromagnetic physics doesn't have such a gaping flaw.19 - . Muttom . Rel. However. G. [perhaps the concept of 'lines of flux' doesn't apply to the e-field generated by a changing magnetic field?] Dept. I cannot see my error.C.Seminar Report on Homopolar Generator 2011-12 if I've made an error in visualizing it.P.20 - . Muttom .T.of Electrical & Electronics Engg. G. Muttom .  It is relatively small size.T.C.P.21 - .  The current produced by the generators does not pulsate.  It have high thermal and dynamic stability. 2011-12 Dept.of Electrical & Electronics Engg.Seminar Report on Homopolar Generator ADVANTAGES  It include a reliable and simple design. 2011-12 o Electromagnetic pumps for liquid metals Dept.22 - .P.of Electrical & Electronics Engg.T.  For eg: o High power electrolysis equipment. o DC electromagnets.Seminar Report on Homopolar Generator APPLICATION  Homopolar generator are employed as the power supplies. Muttom .C. o Arc furnaces. G. but large research generators can produce hundreds of volts.C. or Faraday disc. A potential difference is created between the center of the disc and the rim (or ends of the cylinder). because the homopolar generator can be made to have very low internal resistance.[1] They are unusual in that they can source tremendous electric current. Dept. G. Muttom .P.Seminar Report on Homopolar Generator 2011-12 CONCLUSION A homopolar generator is a DC electrical generator comprising an electrically conductive disc or cylinder rotating in a plane perpendicular to a uniform static magnetic field. acyclic generator. some more than a million amperes.of Electrical & Electronics Engg. The voltage is typically low. and some systems have multiple generators in series to produce an even larger voltage.23 - . It is also known as a unipolar generator. disk dynamo. on the order of a few volts in the case of small demonstration models.T. the electrical polarity depending on the direction of rotation and the orientation of the field. M. vol. Philosophical Transactions for the Royal Society of London.O. T. Carden.U.C. Hibbard. Oct. Rassbach. R. 195 (1962). J.. 1. 'The large homopolar generator at Canberra: initial tests'. pp.P.. The Electrical Engineer. Nature. 31. N.of Electrical & Electronics Engg.Seminar Report on Homopolar Generator 2011-12 REFERENCES  Losty.Y. Sept. Muttom .A. "Notes on a Unipolar Dynamo". See sec.  Hill. H. E. Series A. pg. "Aurora on Uranus – A Faraday disc dynamo mechanism" (1983) Planetary and Space Science (ISSN 0032-0633). 1994 . 45  Hannes Alfvén and Carl-Gunne Fälthammar.24 - . p. Cosmical Electrodynamics (1963) 2nd Edition. D.. Inall.W & Lewis.  Thomas Valone. G. A. Article 18910902)  J.H. 69-75  Nikola Tesla. (1973) Homopolar Machines.3.L. Dessler. 1983. Oxford University Press. (Also available at tesla. 1891. Blamey. Marshall and Sir Mark Oliphant. Induced electric field in uniformly moving matter. Mathematical and Physical Sciences..hu. 275 (1248).1. P. 113–114. E. 2.K. Integrity Research Institute. "The Homopolar Handbook".W. 1187–1198 Dept.T. L. W.