From: Robert Michaels To: High Voltage List Subject: "What The Hell Good Is It ??" Ahoy, Brothers of the Spark! All right, all right, all right. Now that the holiday excesses of food, drink, and foolish spending are over, and now that we're fully in the wonderful cold crisp days of winter (at least in the Northern Hemisphere) may I modestly propose a return to some lively high-voltage discussion? To that end, I offer to answer the question posed in the Subject line. That question is most often voiced by "outsiders" whom we high-volters invite to view a demonstration of our art, craft and science. The question is also heard around "science" fairs whenever a young exhibitor demonstrates one piece of high-voltage apparatus or another: "Tut, tut, tut, that's all very interesting but what (the hell) good is it??". My own answer to the "Whathehellgoodisit?" question is the compilation below of every conceivable application for high-voltage technology in 20th/ 21st century society. That is, every application of which =I= (and a few friends) could conceive. (Your assistance in extending this compilation is earnestly sought!) For the purposes of my compilation, I've used the following definition of "high voltage": That dc potential difference which is the minimum required to jump an open needle-point spark gap in air at STP. (This is approximately 350-volts, dc.) By extension and analogy, I calculate the equivalent ac voltage to be 350/2^0.5 (that is, the r.m.s. equivalent is calculated by dividing 350 volts by the square root of 2). This amounts to approximately 247.5 V. r.m.s. I know this low-ish voltage will baffle some and infuriate others, but, the line has to be drawn somewhere and if it's high enough to jump an air gap at STP, well ... so be it. However you can all relax, in practical terms the overwhelming bulk of the compilation involves voltages which are capable of producing quite respectable arcs, sparks, flames, discharges, brushes and coronas, etc. (yes - Yes - YES!!) and about which even the most unsophisticated will say "Yeah, =that= is high voltage!" FWIW - in the realm of avionics for high altitude and aerospace applications, some of you might be quite seriously astounded at how low a voltage is required to produce a glow discharge at, say, 40,000 ft! And concomitantly, how low a voltage do designers in that field consider dangerously "high" re breakover and leakage, etc. The items in the compilation are more or less in random order, as they occurred to me along with the help of a couple of astute friends and a few bottles of wine on one or two fall evenings. If you perceive some degree of duplication or overlap, well, they were good friends and it was a really good wine! Note that in this compilation of practical applications, I'm not the least interested in =sources= of high voltage - that is, in how it's generated or produced. (That'll be another compilation!). - - - - - - - - - "What The Hell Good Is It?" * CRT Power Supplies - as used in TVs, video displays and projectors, scientific apparatus. Interestingly even the low voltages in TVs etc. are derived from the high-voltage supply in many modern designs * X-rays. The applications for x-rays themselves would make quite a list. Suffice to say medical and dental imaging; therapy; industrial testing; security; crystallography; and that all-important one: fitting shoes in shoe stores (anyone remember?) * Diathermy. (Who recalls?). Time was every physician's office had a diathermy machine and home units were sold as well. Any which can still be found make excellent bases upon which to build a small to medium T-coil. * Particle Accelerators: From the earliest linears, to the Cyclotron to the Superconducting Super Collider * Insect Killers. A UV light draws night-flying insects into a charged grid. Zap!! * Ozone Generators. Ozone is an industrially-important reactant. It is also used in water and air purification * Electrostatic Precipitators. Made in sizes for home use all the way up to industrial behemoths - youwouldnotbelivehowbig. * Engine Ignition. Not only Otto-Cycle gas and gasoline engines but turbines and jets as well. Achieved via magnetos as well as induction coil circuits. * Piezo-Electric Igniters. Simplest example - a butane "match" for lighting fireplaces and braziers. Also found on gas appliances. Speaking of which --- * Gas Appliances - HV ignition has largely replaced pilot flames which are now considered no-nos by the enviro-nazis. Such include furnaces, water heaters, ranges, dryers. Large industrial gas furnaces have always had HV ignition. * Oil Burners. Have always had electric ignition, and been a source of OBITs for us experimenters * Electric Fences. Keep livestock in, and predators (2 and 4-legged) out. Also, electric weirs. * Electric Chair. Still popular throughout the world for carrying out death sentences. They use, typically, about 500-V. dc. The published descriptions of how these work and the effects they have (and have had in notable cases) is morbidly {and gruesomely} fascinating. (Good reading if have no party to go to on Halloween). * Long-Distance Electrical Power Transmission. The largest single practical application by far. Most power transmission still uses ac transformers, but pioneering work using extra-high voltage (as it's called) =dc= has been done by ASEA (the Swedish electrical giant) and has established this as the preferred mode for long distance transmission. * Artificial Lightning. Goes with the above - testing insulators, towers, transformers breakers, etc. Also used in assessing the safety of homes, vehicles, etc. in storms. * Ionic Propulsion. Proposed and tested experimentally for space craft. * Radiation Detectors. Geiger counters require a high polarizing voltage (or high-ish - some low grade GM tubes can make do with as little as 90-volts), and scintillometers traditionally use photomultiplier tubes which require a scale of increasing voltages on their multiple anodes. Most interesting of all are spark chambers in which a spark (or series of them) traces the path taken by a charged particle (sort of a cloud chamber with showmanship). And speaking of cloud chambers, brief application of an HV field is a standard method for clearing used clouds out of some types of chambers. * Neon Signs. How could we forget. How ubiquitous they neon signage is - and now luminous discharge tubes (technical name) are widely used for decorative interior lighting (including residential) and even see automotive use as well! Note: If you know of any conventional iron-core neon sign transformers anywhere, get them! They are going out of style at a very high rate of speed, being replaced with solid-state Tesla/Oudin designs a la TV high voltage power supplies. Bummer! * High and medium pressure arc lights. Most notably xenon arc lamps for theatrical and security uses. They require a high striking voltage to start and some of that low-ish high voltage to sustain the arc. Perhaps we can include mercury vapor lamps (now obsolescent) and high-pressure sodium vapor lamps as used for general illumination in commercial and industrial establishments. * Strobe Lights. For photoflash, signaling. Even disposable one-time use cameras now have them. (Got the picture?) Also used in chemical flash photolysis and for optically pumped lasers. * Rail Guns. Whether this is to be considered a "practical" use is debatable. Perhaps it would be more accurate to say "Rail Gun Research & Development". * Lasers. Like girls who'll make love on the first date. Some do and some don't. Require high-voltage that is. Lasers I mean ... * Exploding Wires. This is more research perhaps than anything "practical". Still, a lot has been learned from the study thereof. Among other things they're a very strong source of ultra short light pulses and rich in very shortwave UV. * Chemical Reactions in Electrical Discharges. The production of ozone and nitrogen oxides is the only large-scale application I know, but many inorganic and organic reactants have been investigated. "Electrical discharge" includes atmospheric pressure arcs and sparks, brush discharges, and low-pressure glow discharges including those using Tesla currents. * Direct Reading Spectrophotometry. This is a very important analytical tool in many industries. The metallic specimen is machined into two pencil-sized pointed electrodes. A HV discharge is established between the two points and the resultant UV light is analyzed by means of a diffraction grating and measured by phototubes. * Spectroscopy. A non-metallic specimen can be placed in a cavity in neutral electrodes and sparked as above. Applications in forensic investigations, analytical chemistry. Also, the spectrum of glow discharges in rarified gases has been extensively studied spectrographically. NOTE: Many texts on spectroscopy discuss the generation and control of the types of HV discharges (generally arc-like oscillatory sparks) of interest to spectroscopists ("Spectroscopists" - try saying that three times and fast after a like number of glasses of wine!). * Plasma Research. Well to consider while we're in a research vein. Some plasmas have nothing to do with high-voltage and others are initiated by HV discharges of one sort or another * Investigations in Atmospheric Electricity, including lightning in all of its forms, sferics and "whistlers", St. Elmo's Fire, electrical storms. * Nuclear Fusion. Neutron generation and fusion can be initiated by specialized HV apparatus which amounts to a sort of plasma globe with a college (or rather graduate school) education. The esteemed Mr. Richard Hull of This List has posted extensively on the very subject. Neutrons can also be generated in other ways using the discharge of a really large capacitor bank and special apparatus. * Fluorescent Lights. Again, some do and some don't - use high-ish voltages. Traditionally, fluorescent lamps have been started by an inductive kick from a small thermostatic starter device. More modern lamps are self starting due to HV (low-ish HV) ballasts and some which are not so low-ish, particularly those used single-pin instant-on fluorescent fixtures. * Anti-Static Applications. The control of static electricity is paramount in some industries (e.g. semiconductor manufacture). Sometimes the best way to precisely neutralize a static charge is to use an opposing HV field. Regardless, knowledge of static HV principles is a must (e.g. charge accumulation at points, the Faraday effect, electrostatic induction, etc.) * Medical Imaging (Other than x-ray), such as nuclear-magnetic resonance and proton-spin resonance imaging. Although it's a specialized form of x-ray machine I'm tempted to include computed axial tomography (CAT) as well, given its stupendous contribution to the medical field. * Cardiac Defibrillators. They only use about 500 volts more or less, same as with electric chairs. The difference is, with the defibrillator the charge delivered is a precisely metered capacitor discharge. (With the electric chair, you just let 'em fry) * Personal Defense Devices. Intended to deliver a strong electric shock to a combatant. Along the same principles: cattle, hog, (and other) electric livestock prods. Also, the Tazer weapon. It shoots two hooks into the victim. The hooks are tethered to the weapon with fine copper wires. After the hooks are set in the enemy, a strong electrical jolt (or multiples of them) are delivered via the wires. * Electrophoresis. It resembles chromatography as a chemical analytical tool. A chemical mixture is spotted onto an absorbent media and an electric field is applied along the media (about 300 - 500-V. dc). The mixture is thus caused to separate into its constituant parts. * Electrocautery. It's a surgical tool both for cutting and for sealing off blood vessels and the like. I don't really know what the voltage involved is but it's high enough to cause arcing. * Electrotheraputics. It's largely obsolete now, but in the early days of electricity, electrical currents of all types where thought to be able to cure various maladies. Modalities included applying sparks (and lower voltages as well) to many parts of the body. Oddly, currents from differing sources were thought to have differing benefits, e.g. galvanic electricity (from batteries) as compared to static electricity. Fascinating to read about in old medical texts and practitioners' manuals. The last remaining vestige today: electroshock therapy for mental illness. * Electrocoating / Electrodeposition / Electrostatic Spraying. All are modern processes for painting work pieces. The paint or pigment is charged and is thus attracted to the grounded work piece, or vice versa. * Photocopying / Laser Printing. Typically, a very thin wire is charged to several thousand volts and this inductively charges a semiconductor drum on which the image is subsequently formed in toner powder. Some older photocopying processes used a HV power supply to charge a special high-conductivity paper having a photosensitive coating. * Microwave ovens, including industrial microwave heating.. Every one has an HV transformer and rectifier. Industrial ovens can be as big as walk-in refrigerators and will sure as hell cook your goose if you're trapped inside of one with the power on. * Broadcast transmitters. Radar. In high-power radio frequency oscillators and amplifiers, vacuum tubes still rule. Plate voltages from several thousand to perhaps around ten thousand are encountered. (Yea!) * Chemical Manufacturing. I list this on speculation (in accord with the well established principal of CYA): Nitric acid, cyanides; carbides, and other commercial chemicals are surely manufactured by means of electrical arcs - but - how high are the voltages? I put it to all of you collectively ... * Induction Heating / Induction Hardening. An rf power oscillator pumps power in the ten-to-several-hundred kilohertz range into a coil specially shaped to match the contours of a work piece (itself typically of a ferocious metal). The work piece quickly becomes red hot in those places in proximity to the coil. Such oscillators make excellent drivers for large vacuum tube (and nowadays, solid state) Tesla coils. * Photomultiplier Tubes. Mentioned above in reference to radiation detectors, they have daily application in detecting ultra-short wave UV, for which semiconductors are yet inadequate. * Infrared Image Tubes. Infrared light focussed on the input side yields a low-contrast image in greenish visible light on an integral output screen. Security, recreational and military uses. * Vacuum tubes (electronic), especially the higher-power transmitting and industrial types. These were noted above in specific contexts, but I list them here and now to be officially all-inclusive of the many kinds and types still in daily use. Includes various types of specialized image tubes of which CRTs are but one. * MIG/TIG Welding. MIG and TIG are forms of arc welding. If nothing else HV-wise is involved, the MIG/TIG arc is started (automatically) by a Tesla current spark, after which the much lower voltage welding current commences to flow. MIG = Metal Inert Gas and refers to the use of a continuous consumable wire welding electrode which also serves as the filler metal. TIG = Tungsten Inert Gas and uses a long-lived tungsten point to strike and maintain the arc with filler metal being supplied separately in the manner of gas welding. "Inert Gas" refers to the use of an air-excluding blanketing gas. * Plasma Torch. These are fun! They are the electrical equivalent of an oxy-acetylene cutting torch. A very bright and disconcertingly loud snappy arc is established between the torch and the ferrous work piece and the resultant heat slices thru formidable chunks of metal as if they were grandma's chocolate cake. I frankly don't know how high the voltage is, but anything this much electrical fun ...!!!... I hereby declare it to be HV even if only on an honorary basis. * Medical Tesla Coils. It's a thing of a bygone era; a hand-held cylindrical device approximately like a modern-day (personal - very personal) vibrator. It plugs directly into the wall and generates a unique Tesla-like spark intended to be applied to the body for medical purposes. Various evacuated tubes could be plugged into the end of the device in place of the pointed electrode and likewise applied to the body. (See also Elecrotheraputics, above). FWIW -- Wimshurst (and similar) machines and induction coils have been used for medical "treatments" from their inceptions -- great for physicians with a sub-speciality in S & M. (Doctor Mengele would have been delighted). * High-Vacuum Leak Testers. These devices are essentially identical to the above, except heavier duty in construction. They are intended to be applied to laboratory glass apparatus which has been highly evacuated. The minutest pin-hole leak will cause the spark from the tester to migrate to that point and thus reveal the existence of the leak and its location. These devices are worth owning. They are made and sold today and available from professional lab supply houses. Even if you don't find any leaks in your glassware, can still use it for your chilblains, ague, feverblisters, or lumbago. * Insulation Testers. Transformer Oil Testers. What more needs be said? A specimen is placed between two electrodes and a high voltage applied while the leakage current is measured. * Megohm Meters. To read into the multi-hundred or thousand megohm ranges, one needs to apply voltages in the 500 - several thousand volt ranges. * Transient and Pulse Testing of Power Equipment. "High-Potting" (High Potential Testing) of consumer and commecial electrical goods. * EDM - Electrical Discharge Machining. An arc is established between a shaped electrode and a work piece, typically under an inert dielectric liquid. The technique allows the making of intricate cuts in very hard or tough alloy work pieces. In a variant, the electrode is a wire and either the wire or the work piece is manipulated during the cutting by a 3-axis servo (CNC) system. By this means, oddly shaped openings can be cut into work pieces (such as elliptical holes). * Neutron-Generating Tubes. Neutrons can be generated (for research or medical uses) from specialized vacuum tubes akin to x-ray tubes. These tubes are articles of commerce. Do not confuse with neutron fusion devices listed near top of this compilation. Such are very much more experimental than they are off-the-shelf products. * Motion Picture and Television Special Effects. Have you seen most any sci-fi or fantasy production releases lately? Make that, in the last ten years? Egad! I love HV but give it a break already! Actually, operating HV apparatus was a standard prop of most sci-fi movies of the '20s, '30s, and '40s. Nowadays we just see the discharges, rarely the equipment which produced them. * Interrogation and Torture. We scarcely ever link these two in the West, but I assure you they are very much a part of things in the 3rd World -- and high voltage does have a role to play. (Are we all adults here, or what?) Contact Amnesty International for further details * Dielectric Heating. This is widely used in industry, typically for gluing-up large assemblies. It's used in the making of automobile interior door and roof panels and in the manuf. of plywood: Alternate layers of wood and adhesives are laid up and compressed between giant electrodes thus to form a large capacitor. A high frequency current (from transmitting-tubes) is impressed across the capacitor and the dielectric losses heat the plywood sandwich and form it into a single sheet. It's quite amusing to make a lab-scale version of this in the 50-100 watt range and use it to fix yourself a real sandwich - like the kind you can eat. Grilled cheese is my own favorite. You have to tune the oscillator so the sandwich properly loads the amplifier - but grilled sandwich tuning is a whole other subject. (Try not to let melted cheese run all over your electrodes) * Field Emission Microscopy. An incredibly fine wire is charged to a high voltage. Electron emissions from the tip thereof are focussed onto a fluorescent screen. The patterns of light and dark on the screen reveal the atomic/molecular structure of the wire. * Electron Microscopy. Scanning Electron Microscopy. I do believe you would all know what those are. * Electron Microprobe Analysis. Kissing cousin to the above. An analysis electron beam is guided to those surface features of the specimen which are of special interest. Resulting emissions, e.g. x-rays, are then analyzed. Made the semiconductor industry what it is today. * Electron Beam Welding. Generally akin to the above, except the electron beam delivers considerable power and results in a sort of spot welding. Also, the work piece need not be microscopic and can in fact take two men to carry. * Pet Collars. Use for training purposes, via a handheld radio transmitter, or for restricting a pet to a given area, via signals from a buried cable. * Discharges in Low Pressure Gases. This is more of a research topic than a practical application. Still, it has been the subject of quite a lot of technical and scientific papers. * High Voltage Artwork. I'm reminded of a wonderful HV kinetic sculpture exhibited by ASEA in connection with the promotion of its extra high voltage dc transmission line technology. Also, lightning fields; plasma globes and plates; and various similar HV objets de art seen at Sharper Image and from time to time in various art galleries. * Kirlian Photography and Lictenberg Figures. I'm not at all sure how practical this all is, unless of course you're heavily into the paranormal. (Have you had your aura checked, lately?). * Kerr Cells. Certain liquids, such as carbon disulfide, become birefringent when subjected to an intense electric field. This becomes a way of producing a very high-speed optical shutter -- if you don't mind discharging high voltage capacitors around liquids which are as flammable as diethyl ether. * Electrets. It's a piece of plastic (broadly interpreted) which is prepared in such a way as to have a permanent electric charge. Much used in some types of microphones and speakers. * Beam and EMP Weapons and research. EMP = Electro-Magnetic Pulse * Mass Spectroscopy. A combination of electric and magnetic fields separate an ion beam into its component parts according to atomic or molecular weight. An important tool found in most any serious chemical or physics research laboratory. * Education and Training. Van DeGraaff generators, Wimshurst Machines, and Induction Coils have been fixtures of school physics labs forever. Likewise, Crookes, Geissler, and kindred evacuated tubes. I vividly recall safety demonstrations put on by the local power company years ago. They used a reverse-run pole pig to show how sizeable flaming arcs (Yes! Oh, Yes!!) could be drawn to green tree branches and to otherwise encourage caution around power lines. * Very Large Electric Motors. Industrial electric motors (in the multi-hundred horsepower size) can be had at operating voltages as high as 10-kV. These can stand 10 or 12 feet high. * Public Entertainments. This could be a longish list in itself. Some which come to mind are the various very large Tesla coils on public exhibit such as the one at Griffths Observatory at L.A. and that at the Boston Science Museum, and at Pittsburgh (*); The large Van DeGraaff generators at various science museums; the Moody Bible Institute presentations; Numerous Jacob's Ladders; Large exhibition size plasm globes; The spectacular GE electrical theater at the 1939 World's Fair in N.Y.C. --- and --- all of us who have startled, amused, shocked (emotionally, that is), and given brown underwear to (intentionally or otherwise) our friends, neighbors, and relatives with demonstrations of our own. (*) The Boston, the L.A., and the Pittsburgh Tesla coils look more spectacular =before= the power is turned on. Their performance is =quite= anemic given their impressive physical size. So don't hasten to make travel arrangements. They are either shorted internally or seriously mistuned or have the wrong type capacitor, or are overall leaky from old age. In Pittsburgh I was told their coil is intentionally under-driven to "protect the public" ! - - - - - - - Well, that's about all we could think of, my buddies and I. We're planning another get together, this time in front of a blazing log in a massive stone fireplace, and with several more of those bottles of wine. Plus, a few Jacob's Ladders and Plasma Globes going in the background for inspiration. If we come up with anything interesting (other than a good high!) I'll surely let you know. Meanwhile ... Please add to the compilation if you can; if you will. Surely we haven't thought of everything. Yet. Listing - to the high-voltage side - in --- Detroit, USA Robert Michaels