2 @25 Asfer\'s Whimshurst-Machine PDF

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Summary

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Description

Whimshurst Machine

Asfer Rasool

14-EE-25

Sec A

1. Problem Statement

To design a Wimshurst machine in order to understand the principle of electrostatics and its fabrication.

2. Aims & Objectives Aims:

 To reproduction of an 1883 Wimshurst Influence Machine that would produce static electricity with electrostatic induction.

 To improve on the design of the machine through experimentation and using a different configuration of components. Objectives:

 The need for a generation of high voltage spark without seed input.  To investigate the potential of Electrostatics.  To use innovative methods to generate a High Voltage. 3. Methodology 3.1

Theoretical Studies Wimshurst generator is an electrostatic machine that produces high DC voltages by induction. The class of electrostatic machine that Wimshurst belongs to is influence machines. Because the charges are distributed on the machine by influencing each other to have cumulative charge generation. Two opposite rotating insulator disks with metal sectors on it distribute the charges such a way that, negative charges are collected in one capacitor, positive charges in the other. In this study, a Wimshurst generator is designed and constructed using commonly available materials.

3.2

Experimental Set Up

After comparing different designs the dimensions of each component is measured for the desired output voltage diameter of insulator disks is selected to be 36 cm so that we can have our desired output voltage. A shaft system is also required in order to supports these disks that could be powered by handle. The setup consists of:

1. Strong wooden base to support the disks and shaft system. 2. The thickness, diameter and material of disks are very important. 3. Radii of spark globe and its material for spark gaps in which ionization and sparking will occur. 4. A shaft system with pulleys and O-ring belts for dynamic mechanism. 5. Leyden jar would be selected keeping output voltage in mind.

3.3

Method of Analysis Insulator disks of Wimshurst generator are very important in the course of design. The thickness, diameter and material affect the outcome. In this study, thinnest possible discs are chosen in order to increase charging by induction. Since the disks should be strong enough to not bend or be deformed during rotation. To supply the necessary strength with the desired dimensions, fiberglass material is used for the disks. 16 metallic sectors are attached to both of insulator disks. Conductor band is used for sectors for the sake of convenience. After sticking all the sectors to both of the disks without leaving any air bubbles, rotating insulator disks are completed. Insulator disks are rotated manually by a pulley- belt- handle assembly. Upper pulleys are placed in the center of the disks, disks and upper pulleys move together. Roller skate wheels are used as upper pulleys since the wheels already have bearings inside. Wheels have a diameter of 6.7 cm. They should be connected to bottom pulleys via a belt. In order to make this connection; belt should be placed

in a slot in wheels. Wheels are carved in lathe stand with the same thickness of the belt. 0.5 cm wide, 0.5 cm deep slots are prepared to have a firm connection. Bottom pulleys should be much bigger than the upper pulleys to rotate them faster with lower force. In this way, when the handle rotates bottom pulley one tum, upper pulley rotates more than one tum due to the difference between their diameters. R1n1=R2n2 The condition of bottom pulleys is important for upper pulleys to rotate stable and its number of turns. After some trials, it is noted that polyamide material gives good result for operation in terms of bedding and bearing. The diameter of bottom pulley is 14 cm and thickness is l.5 cm. A slot having the same dimension with slot on the upper pulley is prepared for both of the bottom pulleys. A rubber belt connects bottom pulleys and upper pulleys. A handle is attached to the bottom pulley of back disk and when it moves, two insulator disks will rotate in opposite directions. Output electrodes are built by connecting two spheres and chrome-coated rod. Electrodes with handles are designed to have an adjustable electrode gap. Collecting combs are also welded to chrome-coated rod. One end of the rod is connected to capacitor, the other end to a spherical electrode. Brushes help Wimshurst generator to distribute the charges so that opposite charges are collected in different capacitors. Double-ended brushes are built by connecting a piece of multi conductor wire to both ends of a chrome-coasted pipe diameter of 0.4. This assembly is prepared for each insulator disks and placed on the supports that hold the disks perpendicular to each other. Brushes touch the metallic sectors on the disks and charge opposite sectors by induction. Two Leyden jars are built in cylindrical form by using 2 mm thick acrylic glass tube. Heavy-duty aluminum foil is wrapped around the acrylic glass tube to form outer

electrode of the capacitor. Another sheet of foil is inserted into the tube. This way, a co-axial cylindrical capacitor is built. Insulator disks and pulleys are placed between two wooden supports. Upper and bottom pulleys are connected by O-ring belt, one twisted to make opposite rotation. Double-ended brushes are placed carefully to have complete connection at all times. Collectors and discharge electrodes are connected to Leyden jars. After assembling all the parts, output voltage is measured by electrostatic voltmeter with 100 kV range. Outputs of Leyden jars are connected to the electrostatic voltmeter. When the drive pulley is rotated manually, it is seen that the desired output voltage is not met. Material selection, design, construction procedure and ambient conditions are all factors in the performance of Wimshurst generator. Therefore, it is possible to increase the performance by making small changes in the design.

3.4

Result Expected

The expected output voltage unfortunately is not achieved by this design. Insulator materials, conductive materials are chosen carefully. Drive components might be improved to have more stable movement. Capacitance of Leyden jar is measured after construction. The measurement and calculation are found to be compatible. In order to have higher voltage levels at the output, capacitances might be increased. Increasing capacitance without changing the other design components is possible by filling the Leyden jar with insulating oil. When the necessary changes are applied, desired outcome will be achieved.

4. Utilization of Results

Whimshurst Machine is mainly used for demonstration purposes, to show the working of electrostatics and is one of the ways to produce high voltage. It can also be used to test circuit breakers and transformers but in the modern age these are tested by new methods....