Power supply required for electrolytic process is low voltage DC supply. For electro-deposition a power supply of 10 to 12 volts which can give 100 to 200 amperes is adequate. Using a suitable conversion such a supply can be obtained from ordinary 220 volts AC supply system.
The conversion from AC to DC can be done by following methods:
(I) Using a Motor-Generator Set:
The motor is an ordinary three phase induction motor and the generator is a heavy current, low voltage DC generator. The generator should preferably be separately excited. DC voltage can be controlled by controlling the excitation of the generator.
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(Ii) By Using a Copper Oxide Rectifier:
It gives better efficiency at low voltages especially at low loads, occupies less space, has low maintenance cost and hence it is preferred.
A mercury arc rectifier is not used because it gives poor efficiency at low output DC voltage on account of constant voltage drops at cathodes and anodes.
Recently the solid state rectifying devices employing germanium and silicon diodes have been developed for use. These solid state devices occupy small space even as compared to metal rectifiers. Output DC voltage can be controlled by controlling the excitation of the generator in the case of motor-generator set by means of continuously variable auto-transformer in case of rectifier supply. When only bath is being supplied then this method of voltage control is suitable. When there are more than one bath to be supplied then a variable resistance is connected in series with each bath so that the supply to each bath can be controlled independently.
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The voltage of each cell is about 10 volts, but if many cells are connected in series, voltage of the order of 500 to 800 volts and current of the order of several thousand amperes may be needed. Thus, by using heavy current motor-generators, or even mercury arc rectifiers, the required supply may be obtained from the modern grid work.
The extraction and refining of metals require large amount of power of the order of hundreds and thousands of KW. Hence such plants are located near the hydroelectric or atomic power stations. Moreover, such plants have hundred percent load factor which helps in reducing the cost.