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William C. Wysock-N6UXW
Tesla Technology Research
2527 Treelane Avenue
Monrovia, CA 91016-4951
(626) 359-1373

 

DESIGN, CONSTRUCTION AND TESTING OF A LARGE SCALE

MAGNIFIER-TYPE TESLA COIL SYSTEM

 

"I actually used in all these three forms, almost every day, all these devices; and furthermore, I had other methods which are not yet patented, and those are corking fine methods." N. Tesla. [4]

1.) INTRODUCTION AND BACKGROUND.

In January 1994, the design for a scaled version of Tesla's famous 1899 Colorado Springs magnifier coil was conceived. The goals were to use modern construction techniques and materials as an integral part of the overall coil design, seek financial sponsorship to assist in funding the project, and finally, build and test the system in time for exhibition at the 1994 International Tesla Symposium. The original design for the Master Oscillator, (Tesla primary and secondary coils), was to be a multi-layered archimedian flat spiral that would be 20 feet in diameter. The framework supporting these two coils was to be made of fiberglass and form a framework that could be bolted together on location, and would elevate the horizontal plane of the primary and secondary coils 20 feet high above ground. The electrical and physical advantages of this design over Tesla's 49.25 foot diameter helical-wound primary and secondary coils as used in 1899, are well known. Even Tesla had previous practical experience with this form of r.f. transformer winding technique, as witnessed from photographs in his Houston Street laboratory prior to the Colorado Springs development work, and again at Wardenclyffe; Tesla used flat spiral transformer designs. These advantages are the ability to control the voltage gradient distribution along the secondary winding, and an improved coupling coefficient between the primary and secondary, where the primary is wound about the circumference of the outer diameter of the secondary coil, which is the ground point of the secondary. This places the largest amount of secondary coil inductance in a closer magnetically coupled influence of the primary winding, thereby increasing mutual coupling between the two windings, producing higher energy transfer efficiency.

In a high frequency, high voltage transformer, E-field or voltage gradient control becomes a serious concern. Corona losses need to be eliminated or minimized in order to achieve maximum transformer efficiency. In a flat spiral secondary construction where the low voltage or ground point is at the periphery, the high voltage point will be at the center of the spiral. The electromagnetic fields set up in this type of winding produce a Faraday shielding effect on successive turns, reducing stray corona leakage. In Tesla's early development work, this form of control was experimented with, as well as other methods, such as enclosing the entire transformer in oil. It is interesting to note that the modern-day automotive ignition coil (for which Tesla received a patient), combined the attributes of a primary winding around concentric layers of secondary windings, the high voltage end of which is at the center of the winding, and is electrically connected to a silicon steel laminated core. This core material increases the permeability of both windings and, along with the whole assembly being contained in oil, provides a design of smallest size and highest efficiency.

In a Tesla transformer of much higher input power and size, it becomes impractical to employ oil or any ferrous core material. However, the fore-mentioned coupling efficiency of the concentric layer approach with the high voltage end at the center of the construction, becomes a very attractive design feature. The original design for a scale version of the 1899 project using this principle was presented to prospective financiers in February, 1994. It was deemed too expensive and physically large to handle, within the time and budgetary constraints that were imposed. Thus, Model 14M, as this design was dubbed, had to be shelved. In its place, an even smaller design Master Oscillator was substituted of much the same construction as Tesla utilized in 1899. This second design would be 1/5 scale in size and amount of inductance in the primary and secondary windings, as compared to Colorado Springs. The secondary winding would therefore be a single layer helical winding on an open framework. Wood was substituted in this new design instead of fiberglass, in order to further reduce anticipated construction costs. Of all the available types of wood, Sitka spruce was the most desirable (and expensive!) This is the same type wood that large power trans former manufacturers utilize as coil supports in their construction. This wood comes only from Alaska and sells for about $3.00 per linear foot. The physical and electrical attributes of this type of wood are that it is a straight-grained closed-cell growth dense wood, and when properly kiln dried and varnished, makes an excellent insulation support material that is easily machinable, with a low dielectric loss tangent, even at moderately high frequencies and very high voltages. More then $4,000.00 of this material was procured for use as the Master Oscillator upright supports, and the squirrel cage structure for the tertiary or Extra coil form. The lower support framework supporting each coil structure was made from clear Douglas fir and pine wood.

The 1/5 scale version Master Oscillator design was to employ a moderately high degree of mutual coupling between the primary and secondary windings, due to close physical spacing, and decoupling both windings from excessive loading against the ground plane, by physically elevating both windings. The high value of M (mutual coupling), implied a need for a very short dwell or commutation time of the rotary spark gap, or "rotary break," as Tesla referred to in his Colorado Springs diary notes. The commutation time that was determined as optimal, was on the order of 15 microseconds. Designing and building a rotary gap to handle very high levels of input power and voltage, yet provide very short pulse durations, proved to be sizable design challenges.

The initial concept for the rotary gap centered on the use of a salient-pole syncronous motor. The original planned A.C. power input level was to be on the order of 50 KW, with a tank circuit charging voltage up to 60 KV. In order to handle high power and voltage levels, yet produce very short commutation dwell times, the physical size of the spark gap was dictated by the rotating velocity required of the rotary electrodes. These electrodes were configured as dual pairs of 0.50 inch diameter thoriated tungsten round rods with hemi-spherical ends, mounted in the ends of a pair of aluminum rotating arms on a common driveshaft. The stationary electrodes were also dual pairs of the same construction, placed 90 degrees apart at fixed locations around the rotary arms. The geometry of the electrodes with their hemispherical ends and a design speed of 3,600 r.p.m. on the driveshaft, determined the radius of rotation needed to achieve a mechanical dwell duration that approached the original design goal of 15 microseconds. This design had to be compromised somewhat, due to the cost of materials and manufacturing, and practical limitations of available torque from the drive motor, to turn the driveshaft and rotary arms at a speed of 3,600 r.p.m.

Two design approaches to couple power from the motor shaft to the driveshaft were considered; direct-coupled insulated shafting and positive drive belting on electrically and mechanically decoupled shafts. The latter was chosen for the advantages of reduced size and fewer mechanical design problems. A flat positive drive timing belt with a 10 horsepower at 3,600 r.p.m. rating was obtained and phenolic positive drive pulleys for both the motor and rotary arm shafts were fabricated, as well as a phenolic idler pulley to take up torque induced slack on the return side of the belt. This belt exhibits sufficient electrical insulation qualities such that the leakage current to ground from the rotary arm driveshaft is limited to about 3.5 milliamps with 50 KV on the rotary arm driveshaft.

The rotary arms were sized to rotate about a 24 inch diameter circle, circumscribed by the hemispherical tips of the tungsten rotary electrodes. This arrangement limits the spark dwell time from the rotary electrodes to each group of stationary electrodes to the order of 25 microseconds at 3,600 r.p.m. To further reduce spark dwell time, the enclosure housing of the rotary gap was designed to be pressurized with nitrogen gas up to 30 p.s.i. One inch thick clear Plexiglas sheeting was chosen for the enclosure material, which offered the advantages of ease in machining, mechanical strength, and the ability to visually observe the performance of the gap while energized.

The original design capacity for the resonant tank circuit consisting of a capacitor bank, rotary break, and Master Oscillator primary inductance was 0.16 MFD at 50 KVAC-RMS, from four Cornell-Dublier phenolic case pulse units that were obtained surplus. It was not known what dielectric material was used in these units; i.e., mica, mylar or other type of plastic film. The ESR (equivalent series resistance), was measured and the dissipation factor of each unit was rated at 0.36. Additional capacitors were made available to allow for testing with different values of primary tank capacity.

The Master Oscillator primary inductance is constructed from two parallel-connected single turn coils of 500 MCM welding cable, and placed about the periphery of the Sitka spruce upright supports, that form the framework for the secondary coil. The pr imary coil is 12 feet in diameter, and the center-to-center spacing of the two single turns is set at 4.5 inches. This same type cable is used exclusively for all inter-connect wiring, along with 4 inch wide copper strapping for the capacitor bank. The coil form made of Sitka spruce, is supported on a framework of clear Douglas fir framing, elevated 4 feet above ground on 4 porcelain pedestal type insulators. The radius between the vertical centerline of the primary and secondary windings is set at 12 inches. However, provision is made for reducing this distance. The vertical offset between the horizontal centerline of the primary to the first turn of the secondary winding is set at 2 inches, and is also designed for adjustment. The secondary winding consists of 30 turns of mil-spec #4 AWG stranded insulated cable with a 105 degree C heat rating. These turns are spaced 1.8 inches apart, and the diameter of this helical winding on its Sitka spruce squirrel cage form set at 10 feet. The final top turn is connected to a toroid capacity terminal ring 10 feet, 8 inches in diameter, with a cross section of 4 inches. This ring is fabricated from smooth outside wall, light galvanized flexible steel tubing. The toroid ring serves two purposes; to provide an electrostatic capacitive load to the output of the secondary winding and to eliminate the possibility of corona streamer leakage. The transmission line or interconnecting link between the output of the secondary winding to the input of the Extra Coil, is also made of this material. The transmission line is 45 feet in length, the distance between the facing sides of the two coil assemblies. The design of the Master Oscillator coil has proven most effective and satisfactory in all operations.

The Extra Coil which is treated as a self-resonant inductance, utilizes the same construction and materials as in the Master Oscillator. The helical coil form is fabricated from Sitka spruce and three 5 foot diameter fiberglass flat discs. The coil form is 5 feet in diameter and 10 feet in length. 150 turns of #8 AWG mil-spec insulated stranded cable are wound with a spacing of 0.8 inches per turn. 4 inch diameter flexible steel tubing form corona suppression toroid rings and are used as both the first and last turn of the inductance on this coil. A phenolic tube spacer 3 feet in height and 2 feet in diameter is used to support the main toroid discharge terminal. This terminal is hollow spun aluminum, 8 feet in diameter and 30 inches in cross-section. The Extra Coil is supported on a douglas fir wood framework and mounted on a porcelain insulator stand 6 feet 4 inches in height. The overall height of the Extra Coil assembly is 20 feet 4 inches or 6.2 meters.

The original high voltage power supply transformer was nameplate rated as a 25 KVa unit, with tap positions on the low voltage winding corresponding to an output voltage up to 60 KV. The construction of this unit was thought to be conservatively built such that for short periods of operation, its Kva rating could be increased two fold, to 50 KVa. In the original testing of this system at Southern California, it was discovered that indeed the core of this transformer went into complete saturation above the 25 KVa level. Therefore, all of the first (alpha) tests conducted on this system were limited to a maximum a.c. input of 25 KVa. These tests took place between July 16-18, 1994. Due to the shortness of available time, the initial proof-of-performance testing was all that could be accomplished, prior to loading the entire system into a 51 foot long 10 foot high container, for transport to Colorado Springs.

The equipment arrived at Colorado Springs at 9 p.m. on July 20, 1994. The intended exhibit site was to be an outdoor equestrian area known as Penrose Stadium. Setup of the equipment commenced at 7 a.m. on July 21, and the date for exhibit was set as Saturday, July 22. A separate power supply transformer was ordered from a firm in Arkansas, and was scheduled for arrival on July 20 at the exhibit location. This second transformer is a 100KVa unit that stands 8 feet high, weighs approximately 2,500 pounds, and is rated for 240/480 low voltage and 36 KV high voltage. To energize this unit, the ITS planning committee arranged to have a 138 KVa stepdown transformer on location, to connect the stadium's mains at 480 volt down to 240 volt, which is the required input voltage for the custom made 2-bay rack cabinet power supply controller. The physical setup of the Model 13M system requires a work crew of 6, a fork lift, a bucket truck, and a crane. It requires approximately 8 hours, simply to accomplish the physical construction of this equipment. In a large apparatus such as 13M, electrical characteristics and tuning are always widely influenced by the surrounding immediate environment. The reflectivity and conductivity of Colorado's red clay-like earth behaves very differently as compared to the asphalt surface of the (alpha) test site in Southern California and represented significant tuning changes. Perhaps most importantly, the integrity of a master ground reference for the input of the Master Oscillator's secondary coil, was questionable. At the (alpha) test site, the location of a 50KW A.M. radio transmitter installation, with its vast ground point and radial counterpoise system feeding a 5 tower phased array, was available for a master ground reference. At Penrose Stadium, only a series of galvanized steel posts as perimeter fencing was accessable. No ground resistivity tests were possible at either location, due to the short amount of time available. At Penrose, all the equipment was set up on sheets of 3/4 inch thick, 4 foot by 8 foot plywood, which lay upon the dirt surface of the stadium floor.

 

MURPHY'S LAW AND OTHER ANOMALIES.

The equipment setup started the morning of July 21 at Penrose Stadium. NOAA weather services as well as the Air Force base weather data forecast mild temperatures and light wind conditions. All of the equipment was [finally] ready for initial power-up testing as of 11 p.m. The night sky was clear and the temperature had dropped into the low 70's. The rotary gap motor which is slowly raised from 0 up to the running speed of 3,600 r.p.m. by means of a 15 KVa autotransformer, was energized. As the rotary gap approached about 1,800 r.p.m., there was a sudden violent vibration observed, and the emergency E-stop control was activated. A close inspection of the gap showed that the10 h.p. motor was loose on its mounting bolts, causing the positive drive belt to skip as the motor was physically raised up off its mounts by the increase in torque. This in turn, caused the thoriated tungsten rotary electrodes to come in destructive contact with the stationary electrodes, shattering six of these $200.00 rods . In an emergency attempt to salvage what was left, the plexiglass housing had to be field-stripped, the sheared-off electrodes removed, the rotary arms re-balanced with only single electrodes in their two ends, the debris removed from the interior of the 1 inch thick enclosure, and then reassembled. At about 2 a.m. on Saturday July 22, the system was finally ready to be tested.

Several important changes were incorporated in this [beta] test; 1) The original 25 KVa transformer was now replaced by a 100 KVa unit. 2) The mains source could supply up to 138 KVa, instead of only 50 KVa, the limit at the [alpha] test site. 3) For the first time, the use of nitrogen gas to reduce spark gap dwell time, by pressurizing the rotary gap enclosure up to 15 p.s.i., was included. As the system was powered up [successfully] for the first time and slowly raised to about 80 KVa input, long streamer discharges were observed emanating from the 8 foot diameter toroid discharge terminal. These appeared to approximately 25-30 feet in length. Also observed were several heavy [D'Arsonval] type discharges about 8 feet in length, going from the transmission line to ground, at a point approximately 15 feet before the input to the Extra Coil. This was the same type phenomena shown in photographs of Tesla's 1899 machinery. This power-up test lasted for about one minute. The system was then powered down and the equipment inspected. The rotary spark gap enclosure exhibited a dark orange-yellow color to its interior; the result of the nitrogen gas recombining into nitric oxide. As the work crew approached the location of the spark gap for a closer look, the plexiglass enclosure began to develop a large quantity of heat stress cracks at most of the 3/8-16 threaded bolt centers; the result of intense temperature difference between the interior and exterior of the enclosure. It was estimated that the interior temperature had raised over the one minutes' operation at the 80 KW level, from ambient to above 400 degrees F. This observation was validated by virtue of the fact that the phenolic plates that locate the stationary electrode assemblies around the rotary arms, were bubbled on their surfaces and exhibited resin seepage. This observed condition had not been previously encountered at the [alpha] test site undoubtedly because of the significantly lower input power level. Since the system appeared to be usable, in spite of the setbacks encountered, it was decided to stop work for the night and make additional repairs to the rotary gap later in the morning. Several members of the ITS staff volunteered to keep watch over the equipment for the remainder of the night.

 

THE "FIFTY YEAR STORM" AT PENROSE STADIUM.

At 9 a.m. July 22, a local machine shop was contacted to provide six centerless ground 0.5 inch diameter replacement electrodes with hemispherical ends. These were only available in tungsten-carbide instead of thoriated tungsten. The top plexiglass enclosure plate had been removed and machined so that three venting holes could be bored, to increase hot air exhausting from the gap enclosure interior. As the work progressed, the skies over Colorado Springs became overcast and it began to sprinkle. A check with the weather services indicated a "slight" low pressure front was moving through the area and the updated forecast was for clearing by afternoon. As the noon hour approached however, this "slight" weather front had intensified and became a category 1 force storm with gail winds sustained above 70 m.p.h., intense lightning, hail balls 1 inch in diameter, and a downpour of rain that flooded many sections of the area. It was reported that over 6 inches of rain fell in less then 4 hours. The storm appeared to be most intense in the foothill area, where Penrose Stadium is located. The group of volunteers from ITS keeping watch over night on the equipment at the stadium, had attempted to cover the equipment with plastic sheeting. This effort was wasted; all the equipment was covered in red-clay mud and was thoroughly soaked. Standing water up to six inches deep turned the earthen floor of the stadium into a small lake. The storm cleared by about 6:30 p.m., and a close inspection of the equipment resulted in the decision to cancel what was billed as "The All American Electrical Show", which was to have started at 8 p.m. that evening. As it turned out, a second storm came over the area later that night, dumping an additional three inches or so of rain. Long term residents of the area referred to this event as "the fifty year storm".

 

IT'S NOT NICE TO FOOL MOTHER NATURE.

Sunday morning, July 23, the weather was again clear and mild. Further inspection of the equipment at the stadium was impossible; even the forklift with its large pneumatic tractor-type tires could not maneuver, even at the end of the day. It would be two more days of mild weather before the earthen floor of the stadium dried out enough to move the machinery and equipment. One week later, the [damaged] equipment that comprised Model 13M, arrived via a flat bed tractor-trailer rig, back in Southern California. From there, the equipment was placed in storage for 12 months, until July 3, 1995.

 

LESSONS LEARNED (TAKE THREE).

As in any scale Tesla coil system, it is imperative to limit the number of unknown characteristics or variables during development and testing. Ideally, only one parameter is adjusted at a time, noting the results and moving on until all the variables are optimized. This is particularly possible where there is sufficient control over the environment and sufficient time to carry out the development process. On this basis, after the winter rainy season was concluded in Southern California, the Model 13 M Magnifier was [again] set up at the broadcast a.m. transmitter site, beginning July 3, 1995 and ending in late November. The weather at this location allowed the possibility of having the entire system set up outdoors with minimum risk of weather damage.

The a.c. power mains supplied to the transmitter site is 480 volt 60 Hz, 3 phase. Each leg is rated at 300 amps continuous load at this voltage. A new stepdown transformer rated at 480/240 volt and 150 KVa was used to supply power to the 2-bay rack cabinet controller for 13M. A separate safety lockout disconnect switch from the mains buss and a 300 amp 480 volt breaker switch insured adequate personnel safety. A comprehensive testing and development program for the Model 13M Magnifier Tesla Coil was now possible.

The first order of business was to redesign and construct the rotary gap, to handle 100 KVa a.c. power input, without overheating. The idea of using pressurized nitrogen gas to reduce the gap dwell time and quench the arc, was abandoned. In its place, a dual chamber squirrel cage blower directed air into a combined plenum box and then force-fed air into the bottom of the rotary gap enclosure. Care was taken in insuring the direction of air flow matched the rotational direction of the rotary arms. The rotary arms were redesigned with different electrode angles, and the new thoriated tungsten electrodes were electrical discharge machined (EDM) for cross-drilled press fit wrist pins, to insure positive locking of these electrodes in the ends of the rotary arms. The stationary electrode holders were modified to include large surface area aluminum heat sinks for cooling. The tungsten electrodes used in these holders were diamond ground for captive flats on their sides, to insure positive locking with set screws. The phenolic sheets that supported the stationary electrode assemblies were replaced with G-10 epoxy-fiberglass plates. These plates have a considerably higher temperature immunity and physical strength, compared to phenolic.

The original capacitor bank consisting of a 0.16 MFD 50 KV AC RMS unit was still employed when the third test operations began on July 5, 1995. This group was eventually replaced with a second group of surplus capacitors, that were arranged in series parallel, for a combined total capacity of 0.29 MFD. Each capacitor was rated at 0.22 MFD and 50 KVDC. Three capacitors were series connected for a string capacity of 0.073 MFD. at 150 KVDC rating. Up to four strings could be parallel connected. With three strings in parallel, the combined rating was 0.22 MFD at 150 KVDC. These capacitors utilize poly-propylene film as the dielectric. The Extra Coil output discharge length improved with this set of capacitors, compared to the original group, however it was felt that a polypropylene capacitor bank made of new units specifically built for pulsed r.f. oscillator circuit service, would yield the best possible results. Ten new capacitors, each rated at 0.1 MFD and 50 KV pulse, were ordered and series-parallel connected for a combined total capacity of 0.25 MFD at 100 KV pulse. The new capacitors proved to be the most efficient on an input KVa vs. discharge length basis. Throughout this testing session, the following capacities were experimented with: 0. 16, 0.21, 0.22, 0.29, 0.25, and lastly, 0.275 MFD. The latter proved to be the optimum capacity for the primary resonant tank circuit. In addition to varying the capacitance value, the primary inductance was changed from two single parallel connected turns to a single two-turn configuration. The spacing was adjusted between the primary winding and the secondary from a radius of 12.0 inches to 10.0 inches. At this spacing, the rotary gap dwell time was deemed too long in duration at 25 microseconds, and was reset at 12.0 inch radius. Additional turns were added to the base of the secondary coil, which resulted in extreme D'Arsonval discharge breakdowns between adjacent turns. These were so destructive as to melt and sever portions of the #4 AWG wire. After extensive and systematic changes were exhausted, the original Master Oscillator specification was restored, and run with the finalized capacity of 0.275 MFD.

At this point, the Extra Coil was capable of delivering discharges from about 40 to in some cases, over 55 feet in length. Calculations based on the actual input power, the voltage under load supplied to the capacitor bank, the total series inductance value of secondary, transmission line and extra coil, the total capacitance of these, and the repetition rate of the rotary gap, show an output discharge rate of 39 arcs/second at 40 feet in length. The calculated energy of each spark is 0.833 KW, which is 32.4 KW/second.

It must be borne in mind that the location of this test site is a major Los Angeles market A.M. transmitter and antenna farm location. The Model 13M Magnifier system was physically located in the near-field radiation pattern of the transmitter antenna farm. The five tower 3/8 lambda phased array antenna system provides over 8 dBi gain, so that even at reduced power for night time transmission (20 KW input), actual inductance or capacitance measurements on the Model 13M Magnifier system were not possible. However, frequency and time domain measurements were conducted during the operational sessions of testing this Tesla magnifier. Specifically, for frequency domain measurements, an HP-8563A spectrum analyzer and an HP-3561A dynamic signal analyzer were used to measure power spectral density (PSD). Time domain measurements were carried out with a Tektronix 468 digital storage oscilloscope. Calibrated antenna probes were used for all measurements except in the case of the Tek-468, which used a simple "gimmick" vertical wire probe. The plotted results of the HP-3561A and the Tek-468 are shown at the end of this paper. The HP-3561A graphs show the spectral content of 13M to be fairly broad in frequency, with two distinctive peaks at approximately 75 KHz and 87 KHz. The shifts shown in the four graphs reproduced, reflect changes in tuning due to varying the primary tank capacitance. The final graph labeled "last run 9:40 p.m." represent 0.275 MFD tank capacity, and agrees well with the HP-8563A result in photo #4. The illustrations in photos #1-3 are taken from the Tek-468 storage scope. Photo #1 specs: vertical input attn.= max. variable @ 50 volt/division and a horizontal sweep rate of 5 us./division. Photo #2 specs: vertical input same as pho to #1 and horizontal sweep 2 us./division. Photo #3 as above, with 20 us./division. Analysis of photo #1 shows the rotary gap commutating over a 20 us. period, followed by primary coil ring time out to 50 us. Photo #2 shows an expanded horizontal scale to reveal more detail in the rotary gap multiple firing process reproduced at 2 us./horizontal division. Photo #3 at 20 us./ horizontal division, shows the Master Oscillator primary coil ring, followed by the first oscillatory wave train response of the secondary coil. All of the above measurements were conducted on August 19, 1995, and were taken using the second set of surplus capacitors. No measurements were made using the new third set of capacitors, which is unfortunate, as the latter clearly proved to be superior in performance. Following the last series of demonstrations and tests at the end of November 1995, the entire system was dismantled and placed in storage, and has remained as such, to this date.

 

FUTURE PLANS AND FURTHER MODIFICATIONS.

Another test session is planned for the latter part of 1996. At this time, it is not clear if the location will be the same as the first and third test sessions. In any case, the following is a list of planned improvements and modifications, that may result in this system's performance with arc lengths approaching 60-75 feet in length.

1) Raise the Extra Coil elevation above ground from the present 76 inches to 108 inches by the addition of a third porcelain pedestal insulator to each of the four supports. This will aid in decoupling the coil from the ground plane and raise the height above ground of the transmission line, which will reduce the number of D'Arsonval discharges from this line to ground.

2) Add more electrostatic capacity to the existing 8 foot diameter toroid discharge electrode. This will be accomplished by the inclusion of a 24 inch diameter aluminum sphere, placed above the center of the top of the toroid, with approximately 36 inches spacing. It seems clear that the 8 foot diameter toroid alone is not the optimum capacity for the Extra Coil to load into. However, it was the largest size that could be ordered. By adding the sphere, and placing it properly above the toroid, the Faraday effect between the two bodies will effectively increase the surface area and therefore total capacity.

3) Design and construct a sulfur hexifloride (SF6) pressurized gap, to be series connected to the existing rotary gap. This will allow an adjustable commutation time from about 25 us. down to less then 15 us. It will also allow higher capacitor charging voltages before gap firing, increasing the energy per pulse that is delivered to the Master Oscillator.

4) Increase the KVa capacity of the 2-bay rack cabinet power supply controller, from its current maximum capacity of 100 KVa to 150 KVa. This will be accomplished by the addition of three more autotransformers to the voltage control and current control stacks, raising the total from 12 to 18 units. This will be necessary in order to take full advantage of the higher energy operating capability afforded by the addition of the series SF6 pressurized gap.

5) Select a new test site for the fourth testing session that is in a low r.f. environment, to afford a real opportunity to conduct accurate test measurements of both system capacitance and inductance. This can only be done in a quiet ambient r.f. radiation location.

6) One of the most provocative research objectives, that was part of the original impetus for constructing this project, was the idea of using such an apparatus to initiate triggered lightning. With the equipment predisposed in a good location under a densely charged cloud formation, this author believes that this equipment will pose as a viable alternative to the use of small rockets with trailing wires. This attempt may also aid in initiating natural ball lightning phenomena.

 

CREDITS.

The construction of the Model 13M Magnifier Tesla Coil system was and continues to be, a team effort. Many individuals contributed their time and talent to produce the results achieved to date. Acknowledgement of the members of this team is appropriate. The financial partners mentioned in the beginning of this paper are a consortium of individuals from Rosen's Electrical Equipment Company Incorporated, of Pico Rivera, California. Virtually all of the components and materials used to construct 13M were supplied by or through this company. It is through their continuing support, that this project has a future.

Company acknowledgement is made to The O. W. Landergren Company, for providing the 8 foot diameter toroid, Hipotronics Incorporated, for providing the poly-propylene capacitors, Greater Los Angeles Radio, Incorporated, for providing the test site in Southern California, and The International Tesla Society, Incorporated, for providing the opportunity to exhibit Model 13M in Colorado Springs, 1994.

 

REFERENCES.

1) Kotter, R.F., Smith, A.N., "A Study of Air-Gap Breakdown at 28.5 Kilohertz." IEEE Trans. PAS Vol. PAS-102, No.6 (1983) 1913.

2) Corum, J.F., Corum, K.L., "A Technical Analysis of the Extra Coil as a Slow Wave Helical Resonator." Proceedings of the 1986 International Tesla Symposium, International Tesla Society, Inc., 1986, PP. 2-1 to 2-24.

3) Corum, J.F., Corum, K.L., "Tesla Coils-An RF Power Processing Tutorial For Engineers." Proceedings of the 1988 International Tesla Symposium, Inter- national Tesla Society, Inc., 1988, PP. 2-8 to 2-48.

4) Anderson, L.I., "Nikola Tesla On His Work With Alternating Currents and Their Application to Wireless Telegraphy, Telephony, and Transmission of Power." Sun Publishing, Denver Colorado, 1992, PP. 48-179, Appendix II, PP. 169-179.

5) Wysock, W.C., "Modern Spark Gap Technology." Proceedings of the Extraordinary Science Symposium 1991, International Tesla Society, Inc., 1991.

 

ILLUSTRATIONS.

1) Model 14M Magnifier System, side view.

2) Model 14M Magnifier Primary and Secondary Coil Support Frame, plan view.

3) Model 14M Magnifier Primary and Secondary Coil Form, plan view.

4) Model 14M Secondary Coil Outer-most Helix Bobin Support, side view.

5) Model 14M Secondary Coil: 1st Secondary Winding, side view.

6) Model 14M Extra Coil Detail, side view.

7) Model 13M Magnifier System, side view.

8) Model 13M Magnifier Primary and Secondary Coil Assembly, side view.

9) Model 13M Magnifier Primary and Secondary Coil Form, bottom view

10) Model 13M Magnifier Primary and Secondary Coil Form, side view.

11) Model 13M Extra Coil Assembly, side view.

12) Model 13M Extra Coil Detail, side view.

13) Model 13M Secondary and Extra Coil Detail, side view.

14) Model 13M Schematic.

15) Model 13M Comparison notes vs.Colorado Springs Notes (CSN)

16) Model 13M Calculations.

17) Model 13M Power Spectral Density (PSD), HP-3561A Dynamic Signal Analyzer.

18) Model 13M Frequency Domain Measurements, HP-8563A Spectrum Analyzer.

19) Model 13M Time Domain Measurements, Tek-468 Digital Storage Oscilloscope.

 

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