WORKING MODEL OF TESLA COIL - wi-tap.energywi-tap.energy/wp-content/uploads/2015/10/301037.pdfWORKING MODEL OF TESLA COIL Alpana Upadhyay Teaching Faculty * [email protected]

WORKING MODEL OF TESLA COIL

Alpana Upadhyay Teaching Faculty *[email protected]

Somarawala Pirmohammad#,Hajare Ganeshkumar & Ghanchi VasimmahamadBE-ELECTRICAL students

#Department of Electrical Engineering, Faculty of Technology & Engineering,Maharaja Sayajirao University of Baroda, Vadodara-390001, Gujarat, India.

#[email protected]

ABSTRACT-This Paper of, WORKING MODEL OF TESLA COIL is built on base of High Voltage Engineering. A Tesla Coil is a high voltage, high frequency, resonant transformer capable of producing many thousands of volts in the form of lightening like discharges. It was primarily built for experiments investigating x-rays, high frequency alternating current phenomena, electrotherapy, and Wireless Electric Power Transmission. It can transmit the power wirelessly with certain distance depends on its ratings. With this coil, we are able to generate High Voltages with High Frequency.

Keyword- High voltage transformer, High voltage capacitor bank, Spark gap, Primary coil, Secondary coil, Discharge terminal.

1. INTRODUCTION

Wireless energy transfer, by definition, does not require direct electrical conductive contacts. Various systems work by transmitting electromagnetic energy from an external power source through a medium by running a large AC current through an external coil to generate a magnetic flux. The changing magnetic flux induces a current in an internal coil. After his inventions about the poly-phase powering systems Nikola TESLA has focused himself more to experiments 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. The Tesla Coil is an air-core transformer with primary and secondary coils tuned to resonate. The primary and secondary circuits function as step-up transformer which converts relatively low-voltage high current to high-voltage low current at high frequencies. The Tesla Coil demonstrates the fundamental principles of high frequency electrical phenomena. It shows the principles of ionization of gases and behaviour of insulators and conductors when in contact with high frequency electrical fields.

2. OPERATION AND WORKING

As the capacitor charges from the high voltage power supply, the potential across the static spark gap electrodes increases until the air between the spark gap ionises allowing a low resistance path for the current to flow through; the “switch” is closed. Once the capacitor

has discharged, the potential across the spark gap is no longer sufficient to maintain ionised air between the electrodes and the “switch” is open. This happens hundreds of times a second producing high frequency (radio frequency) AC current through the primary coil.

The capacitor and primary coil produces an LCR (inductor-capacitor-resistor) circuit that resonates at a high resonant frequency. The secondary coil and top load also create an LCR circuit that must have a resonant frequency equal to the resonant frequency of the primary circuit. The high resonant frequency coupling of the primary coil with the secondary coil induces very high voltage spikes in the secondary coil.The top load allows a uniform electric charge distribution to build up and lightning like strikes are produced from this to a point of lower potential, in most cases ground.

The coupling between the primary and secondary coils do not act in the same way as a normal transformer coil would but works by high frequency resonant climbingor charging to induce extremely high voltages. The true physics is still not completely understood but can be modelled experimentally.

3. CONSTRUCTION AND DESIGN LAYOUT

3.1 High voltage power supply: There are a number of alternative power supplies that can be used for Tesla coils. The most common power supply used is a neon sign transformer (NST). These are used to power neon gas tubes for commercial sign purposes. Their voltage output can vary from about 2,000V to 15,000V and can have a current output from about 10mA to 120mA.

13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India

National Conference on Recent Trends in Engineering & Technology

There are two different types of NST the older iron cored and the newer switch mode NST.

The newer switch mode NST�s are not ideal for Tesla coil use as they have built in GFI ground fault protection, short circuit protection and their components cannot withstand high frequency radio currents – they will simply be fired if they work at all under Tesla coil conditions!

Other high voltage power supplies that can be utilized for Tesla coil use are Ignition coils from cars, oil burner igniters, fly-back transformers, microwave oven transformers, medical X-ray transformers and power distribution transformers, also known as pole-pig transformers.

3.2 Spark gap measurement and arrangement:Spark gaps are the "brain" of the Tesla Coil. They are high the voltage switches that allow the tank circuit capacitance to charge and discharge. As performance of the spark gap switch is improved, peak powers in the tank circuit grow without requiring additional input power. When a good coiler sets up and fires a system, the first thing he looks at is his ground. The second thing he looks at is his spark gap system.

There are three Way to classified: A. STATIC SPARK GAP B. ROTARY SPARK GAP C. COMBINED (rotary + static gap, used usually in magnifiers)

The static spark gap is a simple high voltage switch that is very easy to make and operate. As the tank capacitor charges from the high voltage power supply, the potential across the static spark gap electrodes increases until the air between the spark gap ionizes allowing a low resistance path for the current to flow through; the “switch” is closed.

Once the capacitor has discharged, the potential across the spark gap is no longer sufficient to maintain ionised air between the electrodes and the “switch” is open. This happens hundreds of times a second producing

high frequency (radio frequency) AC current through the primary coil.

3.3 High voltage Capacitor:The tank capacitor consists of a high voltage capacitor rated at about two or three times the RMS voltage rating of the high voltage transformer, so if you have a NST rated at 10,000 VAC its RMS voltage would be ~14,000VAC, so the tank capacitor must be able to withstand ~40,000 volts. This is because the primary circuit can have many very high voltage peaks present when in operation which can damage a too lower rated capacitor. The tank capacitance usually varies between about 1nF to about 50nF depending on the resonant properties of the primary circuit design.

[ 3.033nF with 6KV A.C. ]

There are a number of alternative methods for obtaining high voltage capacitors. A very common method of producing such a capacitor is to create an array of smaller rated capacitors, known as an MMC (Multi Miniature Capacitor). The individual capacitors are set in parallel and series combinations to get the desired voltage and capacitance rating. The following two equations are used for calculating the combined total capacitance parallel and series arrays: Cparallel = C 1+C2+C3+........+Cn

Cseries

We use this formula for finding out the capacitance ofh.v. capacitor:

For our design E=2KV Output of HV T/R and I=2mAout current of HV T/R & C=3.1nF

3.4 Primary coil and its design: There are three main types of primary coil (inductor): spiral, helical and inverse conical. Helical coils are wound into a helix of equal diameter. Spiral coils (or pancake coils) are wound into a flat spiral. Helical coils are wound into a vertical helical spiral. Inverse conical coils are wound into a conical spiral with an inclined angle of 30° to45°. The primary and secondary coils need to be loosely coupled inductively (normal mains transformers have high



coupling between separate coils to get better performance and efficiency) to allow the secondary to undergo resonant climbing to very high voltages. The coil is made from hollow copper tubing (micro bore) with a diameter of about 6-8mm. A frame is constructed to support and fix the copper coil in place. The frame is usually made from sheets of a good insulator like polypropylene (plastic chopping boards are a good source for this).

We use this formula for finding out the inductance of primary coil:

Coil diameter (D) =2.5inches (63.5mm)No. of turns (N) =34 Wire diameter (W) =0.0401 inches (1.02mm) Turn spacing (S) =0.00401 inches (0.102mm)

So, Inductances of coil (L) = 46.45µH Self capacitance (C) =

3.353 pF Height of the coil (H) = 1.18 inches (30mm. and so resonant frequency of primary side is 419 KHz.

3.5 Secondary coil and its design:

Secondary coil is a large single layered coil often made with magnet wire. The form of the coil is usually a PVC drainage pipe. This pipe needs to be completely free from moisture and needs to be smooth. Leaving the pipe out in the sun for a few hours will remove most of the moisture. It must then be coated inside and out with polyurethane varnish to seal it from moisture. Each end of the pipe must also be sealed off either with commercial PVC pipe end caps or home-made PVC end caps. Magnet wire is usually used for the windings and need to wound very tightly with no kinks or gaps. This process can take a very long time by hand and the process must be done with care. Once the coil is wound each end of the windings can be temporarily clamped and the whole coil needs to be coated with a few coats of polyurethane varnish until a smooth finish is obtained.The approximate dimensions for the secondary coil are the height of the coil should be about 5 to 7 times the diameter of the pipe used and the number of turns on this pipe should be about 1000. A good starting diameter for a Tesla coil is around 60mm to 80mm. I believe it is easier to design and make the secondary coil and top load first and build the other components

of the Tesla coil around these components as the other components can be adjusted more easily whereas the secondary coil and top load are fixed once built.

We use same formula as written in primary coil for finding out the inductance of secondary because we choose helical shape for primary & secondary both.

Coil diameter (D) =3inches (457mm) No. of turns=930 Wire diameter (W) =0.0177 inches (0.45mm) Turn spacing (S) =0.00177 inches (0.045mm) So, Inductances of coil (L) = 9.99mH Self capacitance (C’) = 6.59 Pf

3.6 Sphere and Toroid Design:

The top secondary winding is directly connected to a top load discharge terminal usually in the form of a toroid or sometimes a sphere. The bottom secondary winding is directly connected to an excellent RF ground connection.

A toroid can be constructed from flexible aluminium air duct hose (used for air conditioning and extraction). The flexible hose is cut and bent into a toroid and fixed together using epoxy resin. The toroid is more efficient with a smooth metallic finish and so it is a good idea to cover the toroid with aluminium tape to provide this smooth finish. The secondary coil has an inductance and due to the high frequencies used it also has a self capacitance. The toroid itself acts a single plate of a virtual capacitor with the air being the dielectric and the ground/Earth acting as the second plate of the virtual capacitor. We use this formula for finding out the capacitance of toroid:

K= 1.01 (dielectrical constant) Radius of sphere (R) =7.5cm so, the capacitance of the sphere (C) =8.416pF



4. RESULTS

After testing our model we got output up to 75KV with 410 KHz which is not constant. After testing it repeatedly we get 60KV with 410 KHz which is constant output.

5. CONCLUSION:

After studying and developing the model of TESLA COIL we came to following conclusion:

1) We are able to generate high voltage with high frequency and it can be used for testing the apparatus for switching surges. 2) It can also be used for study of visual corona and ionization of gases under the electrical stress. 3) It can also transmit the electrical power wirelessly up to certain distance depends upon its rating.

6. REFERENCES

1. High Voltage Engineering By: M S Naidu & V Kamraju. 4th Edition, Tata McGraw Hill Publishing Company Ltd2. The Ultimate Tesla Coil Design and construction guide. By: Mitch Tilbury Published By Tata McGraw Hill Publishing Company Ltd



Documents

WORKING MODEL OF TESLA COIL - wi-tap.energywi-tap.energy/wp-content/uploads/2015/10/301037.pdfWORKING MODEL OF TESLA COIL Alpana Upadhyay Teaching Faculty * [email protected]