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Transcript

International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN(P): 2250-155X; ISSN(E): 2278-943X Vol. 4, Issue 4, Aug 2014, 11-18 © TJPRC Pvt. Ltd. SMALL SCALE HIGH FREQUENCY, HIGH AC VOLTAGE GENERATION USING TESLA COIL G. RADHIKA1 & M. SURYAKALAVATHI2 1 2 Department of Electrical & Electronics Engineering, VNR VJEIT, Hyderabad, Telangana India Department of Electrical & Electronics Engineering, JNT University Hyderabad, Telangana India ABSTRACT The Paper includes Introduction in which the history of the technology was described followed by Circuit Description in which the basic Resonance principle was given followed by Design & Construction in which the desired design aspects were discussed and shown the obtained values followed by Test Results in which the values were tabulated and finally with Observed Conclusions. Generation of High Voltages such as AC, DC and Impulse are required for the several applications in the fields of electrical engineering and applied physics. High frequency high voltages are required for rectifier d.c power supplies and also for testing of electrical apparatus for switching surges, sometimes high voltage damped oscillations are needed which need high voltage high frequency transformers which is commonly used as high frequency resonant transformer is Tesla Coil. This paper presents the design and construction of a TESLA COIL which can generate High voltage in the order of 250KV at a frequency of 250KHz. Tesla coil is an air core and doubly tuned Resonant Transformer which can generate very high voltages in the form of lightning like discharges. It is also used for Wireless Electric Power Transmission for certain distances depending upon the rating. The so designed Tesla Coil our laboratory is used for mainly testing the insulation of various power system components. KEYWORDS: Neon Sign Transformer, Capacitor Bank, Spark Gap, Primary Coil, Secondary Coil, Top Load INTRODUCTION Nikola Tesla who is a Serbian scientist invented Tesla coil, a resonant air core transformer around 1891 which is used to produce high-voltage, low-current and high frequency alternating current electricity. Tesla experimented with a number of different configurations consisting of two, or sometimes three, coupled resonant electric circuits. He used these coils to conduct innovative experiments in electrical lighting, phosphorescence, X-ray generation, high frequency alternating current phenomena, electrotherapy, and the transmission of electrical energy wireless [1]. Wireless energy transfer, which means, does not require direct electrical conductive contacts. Various systems works by transmitting electromagnetic energy from an external power source through a medium by running a large AC current through an external coil in order to generate a magnetic flux hence the changing magnetic flux induces a current in the internal coil. After his inventions in the poly-phase Powering Systems, Nikola TESLA has focused himself more to experimenting with high voltages, high currents and high frequencies. One of his goals was to transmit electrical energy without a power network directly from a central plant to the different consumers. Tesla coil circuits were used commercially in spark gap radio transmitters for wireless telegraphy until the 1920’s and in medical equipment such as electrotherapy and violet ray www.tjprc.org [email protected] 12 G. Radhika & M. Suryakalavathi devices. Today their main use is in entertainment and educational displays, although small coils are used as leak detectors for high vacuum systems [2]. CIRCUIT DESCRIPTION AND OPERATION The below Figure 1, shows the equivalent circuit of Tesla Coil, the basic principle involved in this is, when the capacitor starts charging from high voltage transformer connected to AC mains, and when the voltage across the spark gap exceeds the dielectric strength of the air the spark will jump, connecting the capacitor to primary coil and then the electrostatic energy will be transformed to magnetical energy of the primary coil. It induces the damped oscillations in the secondary coil. The main parts to build a Tesla Coil are Power supply, Primary Capacitors, Spark gap, Primary coil, Secondary coil, Toroid. Figure 1: Circuit Equivalent of Tesla Coil A Tesla coil is a resonating transformer containing a primary and secondary LC circuit where the two LC circuits are loosely coupled together. Power is supplied to the primary circuit through a transformer, which charges a capacitor. Eventually the voltage across the capacitor will increase sufficiently to short a spark gap. The capacitor will discharge through the spark gap and into the primary coil. The energy will oscillate back and forth between the primary capacitor and primary coil inductor at high frequencies (typically 100 - 300 kHz). The primary coil is coupled to an inductor in the secondary circuit, called the secondary coil. Attached to the top of the secondary coil is a top load that provides capacitance for the secondary LC circuit. As the primary circuit oscillates, power is induced in the secondary coil where the voltage is multiplied many times. A high voltage, low current field develops around the top load and arcs of lightning discharge are observed. The primary and secondary LC circuits must oscillate at the same frequency to achieve maximum power transfer. The circuits in the coil are usually "tuned" to the same frequency by adjusting the inductance of the primary coil [1]. Figure 2: Construction of Tesla coil Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0 13 Small Scale High Frequency, High AC Voltage Generation Using Tesla Coil DESIGN AND CONSTRUCTION Transformer A Neon sign transformer of ratings: Primary voltage 230V, Secondary voltage 7500V-0-7500 V, Volt- Ampere rating of 450 VA at 50 Hz, RMS current rating of 22mA and Short Circuit current of 30mA is used to power the Tesla coil primary. Its secondary mid point is grounded to case and load 50 RFT RED 55 RFT BLUE 12 M.M. Figure 3: Neon Sign Transformer The empirical formula gives the maximal length of the sparks only from the output power of the transformer. The phenomenon of gas breakdown is extremely complex, and the arc length depends on much more than simply the voltage at the top load. The basic formula giving the length L of the sparks in centimeters is shown below. P= (L/1.7) 2 or L = 1.7 * √P Assuming input power consumption measured via wattmeter is 40W the maximum expected spark length is 10 inch (25.4 cm). Primary Coil To make a primary coil of Tesla coil a ¼ inch (6.35 mm) copper plumbing tube is used. Leaving about a ¼ inch spacing between turn to turn about 11 turns are made to obtain the inductance of primary to be L1 = 40µH given by formula for a flat spiral coil. Figure 4: Primary Coil With above values, theoretical L1 = 41.4 µH with outer diameter (Do) of 17.5 inch, for the above construction 425 inches of copper tubing is used. The so obtained practical value of primary coil is 42µH. Secondary The dimensions of the secondary former are decided by the following “Tables 1 and 2” [3]. www.tjprc.org [email protected] 14 G. Radhika & M. Suryakalavathi Table 1: Power Vs Secondary Diameter Power Range Less than 500W 500W to 1500W 1500W to 3KW Secondary Diameter 3 to 4 inches 4 to 6 inches 6 to 10 inches Since the power consumption is less than 500W for the NST, the secondary diameter is chosen to be 4 inch. Table 2: Secondary coil Form Dimensions Form Diameter 3 inches 4 inches 6 inches 8 inches and above Aspect Ratio 6 to 1 5 to 1 4 to 1 3-5 to 1 Coil Length 18 inches 20 inches 24 inches 24 inches and above For a 4inch, optimum aspect ratio is given as 5:1 and thus the coil length is decided to be 20 inches. The inductance value of secondary coil is calculated using the formula given below. Figure 5: Secondary Coil With the above values of secondary helical coil on a PVR former, L2 is found to be 24.61mH and self capacitance C=8.165pF with height of coil being 21 inches and lenght of wire 15000 inches.The practical value of secondary coil is 26mH. Capacitor Bank The capacitor bank value is decided based on the ratings of Neon Sign Transformer. The capacitor value is obtained by the formula Z = E (output _ voltage) I (rated _ current ) The so calculated value of capacitor is 4.6nF. More recent experiments suggest that a capacitor value of between 1.5 - 2.0 times the mains-resonant value performs best and is least likely to damage the transformer, and this would be referred to as an LTR (Larger Than Resonant) capacitor value. Therefore a multiplication factor of 1.8 value is chosen for optimized performance which results in final capacitor bank of 8.5nF withstand capacity more than 15KV. Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0 15 Small Scale High Frequency, High AC Voltage Generation Using Tesla Coil Figure 6: Capacitor Bank To obtain the above characteristics in capacitor bank MMC cap value of 0.47F,2kV are used. To obtain with standing capacity and final capacitance value 11 capacitors per strings are used to withstand voltage of 22KV and two such combinations are kept in parallel to obtain capacitance value of 8.5nF. Top Load For ease of construction, a top load is constructed as a toroid for Tesla coil secondary. The most efficient shape for the top load is a toroid and crude rule of thumb is to make the height of the toroid (minor diameter) about the same size as the secondary diameter, and the outer diameter of the toroid (major diameter) four times the minor diameter. . Figure 7: Toroid Shaped Top Load Theoretical Capacitance C2 = 17.674pF. Hence the below table shows the values of both Primary and Secondary Coil inductance and capacitance values for the experiment. Table 3: Primary & Secondary Coil Values Parameters Inductance Capacitance Primary Coil 41.4µH 8.5nF Secondary Coil 24.61mH 17.67pF Spark Gap Spark gap mainly acts as a high power switch which is responsible for initiating the discharge of tank capacitor into primary winding of Tesla coil. The distance between the electrodes is set such that the air between the electrodes breaks when the capacitor is fully charged. With one single large air gap the arc cannot be quenched properly, which results in more power loss. This can be overcome by the construction of several small gaps connected in series to achieve the same breakdown voltage with improved quenching ability and less power loss. To achieve this above aluminum rods of diameter 1 inch and height of 2 inch are used in series as shown below in “Figure 8”. www.tjprc.org [email protected] 16 G. Radhika & M. Suryakalavathi Figure 8: Static Spark Gap and Advanced Spark Gap High Voltage Probe In order to measure the output of the Neon sign transformer a high voltage probe is used which steps down the voltage to a measurable value. The step down ratio is 1000:1 TEST RESULTS A low power Tesla coil is designed with the desired output voltage of 250KV at a frequency of 250 KHz which is fed from a 230V, 50Hz, 1- Φ supply through an auto transformer. Wireless power transmission is obtained at a range of 2 Metres from the top load. The below “Tables 4 & 5” shows the test results of Neon sign Transformer and Spark Gap Testing results. The below “Figure 9” also shows the field around the toroid, which transmits around 2m and above. Table 4: Neon Sign Transformer Testing Results Input Voltage (Volts) 40 80 100 120 160 180 200 230 Output Voltage (Kilo Volts) 6.01 7.47 8.45 9.25 10.54 11.11 13.26 15.36 Table 5: Spark Gap Test Results Distance b/w Electrodes 2 mm 4 mm 6 mm 8 mm Breakdown Voltage (KV) 3.85 7.74 11.32 15.54 Figure 9: Experimental Set up and Field Transmission Impact Factor (JCC): 5.9638 Index Copernicus Value (ICV): 3.0 17 Small Scale High Frequency, High AC Voltage Generation Using Tesla Coil CONCLUSIONS Following conclusions were made after studying and developing the model of Tesla Coil. • Generated high voltage at high frequency, which can be used for Insulator Testing. • Used for the study of visual corona and ionization of gases under electrical stress. • Transmit electrical power wireless up to 2m and above. • Output power obtained by using Improved Spark gap is more when compared to static spark gap. ACKNOWLEDGEMENTS The Authors are grateful to the Department of Electrical and Electronics Engineering, VNR Vignana Jyothi Institute of Engineering & Technology, Hyderabad for the support on this project work. REFERENCES 1. M.S Naidu & V. Kamarajua.(2009). 4th ed. New Delhi: Tata McGraw-Hill Publishing Company Limited, High Voltage Engineering. 2. Mathias Birle, Carsten Len and Stefan Bauer, “Design and Application of a High-Frequency High-Voltge Generator” XVII International Symposium on High Voltage Engineering, Hannover, Germany, August 22 -26, 2011. 3. RichardBurnett, Masters Dissertation in Electrical & Electronic Engineering, University of Newcastle, Retrieved from http://www.richieburnett.co.uk/tesla.shtml. www.tjprc.org [email protected]