ENGINEERING ARTICLES

It is broadly classified into Conventional energy  is in practice for long duration of time and well established technology is available to tap and use them. e.g. Coal, oil, natural gas, hydro power, nuclear power etc. Non-conventional energy source can be used with advantage for power generation as well as other applications in a large number of locations and situations. These energy sources cannot be easily stored and used conveniently. E.g. Solar, wind, tidal and geothermal etc. Based upon nature, energy sources are classified as Renewable energy sources  are inexhaustible and are renewed by nature itself. Solar, wind, tidal, hydro and biomass are few examples. Non-renewable energy sources  are exhaustible within a definite period of time depending upon its usage. Fossil fuels (coal, oil, gas) and nuclear fuels are few examples.

The plasma chambers suspend the silicon and the phosphorus or boron molecules in a gaseous state. This mixture is pushed into a chamber which has electrodes at the top and bottom. When the electrodes are charged an electric field is produced between them. The electric field removes some of the electrons from the mixture so creating a gas of positively charged ions, a plasma. A stainless steel or glass sheet with an indium/tin oxide layer is passed into the chamber and between the electrodes. The plasma-like gas deposits charged particles on to the uncharged surface of the steel or glass substrate. Depending upon the chemical nature of the gaseous mixture fed into the chamber, one of the three layers which make up the photovoltaic cell will be formed. The thickness of the layers depends on the speed at which the sub state passes through the chamber, and the size of the chamber.

In solid dielectrics, highly purified and free of imperfections, the breakdown strength is high, of the order of 10 MV/cm. The highest breakdown strength obtained under carefully controlled conditions is known as the "intrinsic strength" of the dielectric. Dielectrics usually fail at stresses well below the intrinsic strength due usually to one of the following causes. (a) Electro-mechanical breakdown. (b) Breakdown due to internal discharges. (c) Surface breakdown (tracking and erosion). (d) Thermal breakdown. (e) Electro chemical breakdown. (f) Chemical deterioration.

Almost no complete electrical insulation consists of one insulating phase. Usually more than one insulating material will be involved, either in series, parallel or both. The simplest form of composite insulation system consists of 2 layers of the same material. In this case advantage is taken of the fact that two thin sheets have a higher electric strength than a single sheet of the same total thickness. In other cases, composite dielectrics occur either due to design considerations (ex: paper with an impregnating liquid) or due to practical difficulties of fabrication (ex: air in parallel with solid insulation). In certain cases, the behavior of the composite insulation could be predicted from the behavior of the components. But in most cases, the system as whole has to be considered. The following considerations determine the performance of the system as a whole. (i) The stress distribution at different parts of the insulation system is distorted due to the component dielectric cons...

Since no insulant is completely free of ions, a leakage current will flow when an electric field is applied. The ions may arise from dissociation of impurities or from slight ionisations of the insulating material itself. When these ions reach the electrodes, reactions occur in accordance with Faraday's law of electrolysis, but on a much smaller scale. The insulation and the electrode metal may be attacked, gas may be evolved or substance may be deposited on the electrodes. The products of the electrode reaction may be chemically or electrically harmful and in some cases can lead to rapid failure of the insulation. The reactions are much slower than in normal electrolytic processes due to the much smaller currents. The products of the reactions may be electrically and chemically harmful because the insulation and electrodes may be attacked, and because harmful gases may be evolved. Typically a 1 F paper capacitor operating at 1 kV at room temperature would require 2 to 3 years to g...

Surface flashover Surface flashover is a breakdown of the medium in which the solid is immersed. The role of the solid dielectric is only to distort the field so that the electric strength of the gas is exceeded. If a piece of solid insulation is inserted in a gas so that the solid surface is perpendicular to the equipotentials at all points, then the voltage gradient is not affected by the solid insulation. An example of this is a cylindrical insulator placed in the direction of a uniform field. Field intensification results if solid insulation departs even in detail from the cylindrical shape. In particular if the edges are chipped, or if the ends of the cylinder are not quite perpendicular to the axis, then an air gap exists next to the electrode, and the stress can reach up to 0r times the mean stress in the gap. Discharge may therefore occur at a voltage approaching 1/0r times the breakdown voltage in the absence of the cylinder, and these discharges can precipitate a breakdown....

(a) Removal of dust Small dust particles can become charged and cause local stresses which can initiate breakdown. They can also coalesce to form conducting bridges between electrodes. Careful filtration can remove dust particles greater in size than 1 m. The strength of the liquid then increases and greater stability is achieved. (b) Removal of dissolved gasses Liquid insulation will normally contain dissolved gas in small but significant amounts. Some gases such as Nitrogen and Hydrogen do not appear to upset the electrical properties to a great extent, but oxygen and carbon dioxide can cause the strength to change significantly. Thus it necessary to control the amount of gases present. This is done by distillation and degassing. (c) Removal of ionic impurities Ionic impurities in the liquid (particularly residual water which easily dissociates) leads to abnormal conductivity and heating of the liquid. Water can be removed by drying agents, vacuum drying, and by freezing out in...