Power Supply for Electrolytic Process:
Power Supply for Electrolytic Process is direct current and at very low voltage. The power required for electrodeposition is usually very small (between 100 and 200 amperes at 10 or 12 volts) and can be obtained either by employing a motor-generator set consisting of a standard induction motor driving a heavy-current low-voltage dc generator (preferably separately excited) or by employing the copper oxide rectifier. The latter is preferred because of low maintenance cost, occupying less space and higher operating efficiency. Mercury-arc rectifier cannot be used because it has low efficiency at low output dc voltage on account of constant voltage drops at cathode and anodes. The plate rectifier unit is usually placed along with its transformer in the oil so that it may be protected from the corrosive fumes of the electrolyte.
Recently the solid state rectifying devices employing germanium and silicon diodes have been developed for use. These solid state devices occupy very small space even as compared to metal rectifiers. Output dc voltage can be controlled by controlling the excitation of the generator in case of motor-generator set and by means of continuously variable auto-transformer in case of rectifier supply. This method of control is suitable where only one bath is being supplied. In case, more than one bath are supplied, a variable resistance is connected in series with each bath so that the supply to each bath can be controlled independently. With the development of SCRs or thyristors, which can control output voltages of power supplies, their use in power supplies for electrochemical processes has increased. They are also compact and light in weight, even cooling attachments are included. Voltage control is by using output transformers.
Power Supply for Electrolytic Process required for extraction and refining of metals and large scale manufacture of chemicals is in very large amounts. Since most of the processes are continuous, therefore, have a load factor of 100 per cent. Because of power requirements in huge amount and at 100 per cent load factor, such plants are located near the hydroelectric power stations or atomic power stations even if extra transportation of raw material is necessitated. The advantage of a high load factor is greater with such stations than with steam stations and also transmission costs are eliminated. Nangal fertilizer factory producing calcium ammonium nitrate and heavy water and utilizing power of 180 MW from left bank Bhakra power house and Sri Ram Fertilizer factory located at Kota (Rajasthan) are instances in the support of the above statement.
The voltage of each cell is about 10 volts, but if many cells are connected in series, current of the order of several thousand amperes will be required at the voltage of the order of 500 to 800 volts. Thus by employing heavy current motor-generators, rotary convertors or even mercury-arc rectifiers, the required supply may be obtained from the modern grid network.