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The transmission voltage for which the cost of conductors, transformers, insulators, switchgears and other terminal apparatus is minimum is called the economical transmission voltage.As we know, if the transmission voltage is increased, the volume of conductor material required for the transmission lines is reduced. Hence, this decreases the expenditure on the conductor material. It is advisable to use the highest possible transmission voltage in order to reduce the expenditure on the conductor material to a minimum. Although, it may be remembered that as the transmission voltage is increased the cost of insulation, transformers, switchgears and other terminal equipment also increases. ... Read More
Underground Electric Transmission SystemThe system of electric power transmission uses underground cables for transmitting the electric power from the generating station to the consumers is known as underground electric transmission system.Underground cables have low visibility and are not affected by bad weather. However, the cost of these cables is comparatively high and their laying process is also time consuming.Types of Underground Transmission SystemBased on the type of supply (i.e. AC or DC) and the number of conductors used, the underground electric transmission system can be classified into the following types −Underground DC SystemTwo-Wire DC SystemTwo-Wire DC System with Mid-Point EarthedThree-Wire ... Read More
AC (Alternating Current) and DC (Direct Current) are the two different types of electric current that are used in the welding process. AC arc welding is commonly used for down-hand heavy plate welds, fast fills and with aluminium TIG welding with high frequency, while DC welding is better for welding thinner metals. Also, the equipment used for DC arc welding are also cheaper than AC arc welding machinery.The specifications of equipment used in practice for AC and DC arc welding are given as follows −Specifications of AC Arc Welding Machinery - AC transformer − Step down, oil cooled, 3-phase, 50 ... Read More
Resistance WeldingResistance welding is the process of joining of metals by applying mechanical pressure and by passing high electric current for a length of time through the metal area which is to be joined.The process of resistance welding was discovered by Professor Elihu Thompson in 1885 in Philadelphia. It was an accidental discovery, while experimenting with a spark coil operated form a bank of batteries, he accidentally welded two steel rods of about 0.635 diameter.The principle of resistance welding is the production of heat in the weld joint by passing a heavy current through the parts and this being followed ... Read More
In the infrared or radiant heating, the heating elements are of tungsten filament lamps operating at about 2400 °C. As at this high temperature a greater portion of infrared radiation is given to the object for heating. In this method of heating, the heating effect on the object is greater because the temperature of the heating element is greater.With the help of suitable reflectors, which are plated with rhodium, these infrared radiations are focused on the surface to be heated. The lamps used for the heating purposes in this method have ratings varying from 250 to 1000 watts operating at ... Read More
What is Electric Heating?The process in which electrical energy is converted into heat by resisting the free flow of electric current is known as electric heating.Whenever an electric current is made to pass through any circuit having a resistance of R ohms, then power dissipated in the circuit is equal to $\mathit{I^{\mathrm{2}}R}$ Watts. If the current flows for t seconds, then the electric energy consumed in the circuit is equal to $\mathit{I^{\mathrm{2}}Rt}$ Joules. This energy is converted into heat and worked out as $\mathit{I^{\mathrm{2}}Rt}/4.2$ Calories, where 4.2 is a constant called mechanical equivalent of heat.The use of heat produced by electricity ... Read More
Electric ArcAn electric arc is an electric discharge of gases which is produced by passing an electric current between two points called electrodes. The electric arc was first detected by British chemist Humphry Davy in 1808. The electric arc is the visible plasma between two electrodes due to the ionization of gases by the electric current. The electric arc is commonly used in welding, lighting and plasma cutting.Electrical Properties of Electric ArcThe electrical properties or characteristics of an electric arc are given below.Stability of Electric ArcThe electric arc has negative resistance characteristic, i.e. with the increase in the arc current, ... Read More
Carbon arc welding is used for welding copper and its alloys. In this method, the carbon electrode is used which is kept negative with respect to work if DC supply is used. It is because, if the carbon electrode is made positive, the carbon particles have a tendency to go into the welded joint and make it brittle. Therefore, the electrode in carbon arc welding is always kept negative and the work positive.For carbon arc welding, only DC supply can be used. In this welding method, the heat from the arc forms a molten pool and the extra metal required ... Read More
Heating ElementThe device which converts electrical energy into heat energy through the process of Joule heating is known as heating element. The heating element is the part of any electric heating appliance in which the electrical energy transformed into heat. The electric current through the element encounters resistance which results in heating of the element.Requirements of a Good Heating ElementA good heating element should possess the following properties −High ResistivityThe specific resistance or resistivity of the material used for making the heating element should be high. When the resistivity of the material is high, then the element will require small ... Read More
What is a Welding Position?The technique which allows a welder to join the metals in the position in which they are found or the position in which a specific component will be used, is called the welding position.According to the American Welding Society, there are following four welding positions in which arc welding is done −Flat PositionHorizontal PositionVertical PositionOverhead PositionFlat PositionThe flat position is also referred to as down-hand position. In the flat position, the metals to be welded are placed flat and the welder passes the electric arc over them.The important points about the flat position of welding are ... Read More