Most rig power is consumed by hoisting and fluid circulating systems. The other rig systems have much smaller power requirements. Fortunately, the hoisting and circulating systems generally are not used simultaneously, so that the same engines perform both functions.
Total power requirements for most rigs are from 1000 to 3000 hp provided by one or more engines depending on well depth and rig design. Power requirements vary for different drilling jobs, shallow or moderate depth drilling rigs need 500 - 1,000 HP, heavy-duty rigs for 20,000 foot (6000 meters) holes usually need 3,000 hp, Auxiliary power requirements for lighting, etc., may be 100 - 500 hp.
The early drilling rigs were powered primarily by steam. However, because of high fuel consumption and lack of portability of the large boiler plants required, steam-powered rigs have become impractical.
Modern rigs are powered by internal-combustion diesel (or gas) engines .engines and sub-classified depending on the method used to transmit power to the various rig systems as:
1-Diesel electric type.
2-Direct drive type.
Diesel electric rigs are those in which the main rig engines are used to generate electricity. Electric power is transmitted easily to the various rig systems(the diesel engines generate and deliver electric power by cables to electrical then to electric motors attached to the involved equipments) switch gear then to , where the required work is accomplished through use of electric motors. Direct-current motors can be wired to give a wide range of speed-torque characteristics.
That are extremely well-suited for the hoisting and circulating operations. The rig components can be packaged as portable units that can be connected with plug-in electric cable connectors. There is considerable flexibility of equipment placement, allowing better space utilization and weight distribution. In addition, electric power allows the use of relatively simple and flexible control system. The driller can apply power smoothly to various rig components, thus minimizing shock and vibration problems.
Direct drive rigs accomplish power transmission from the internal-combustion engines using system of pulleys, gears, chains, belts, and clutches rather than generators and motors. The initial cost of a direct-drive power system generally is considerably less than that of a comparable diesel-electric power system. The development of hydraulic drive has improved greatly the performance of this type of power system. Hydraulic drives reduce shock and vibrational problems of the direct drive power system. Torque convertors, which are hydraulic drives designed so that the output torque increases rapidly with output load, are now used to extend the speed-torque characteristics of the internal-combustion engine over greater ranges that are better suited to drilling applications. The use of torque convertors also allows selection of engines based on running conditions rather than starting conditions. Power-system performance characteristics generally are stated in terms of output horsepower, torque and fuel consumption for various engine speeds.
3000hp =2237099.615 watt equal to the power operates 22371 house lamps.
The power on modern rigs is most commonly generated by diesel-electric power units. The power produced is AC current which is then converted to DC current by the use of SCR (Silicon Controlled Rectifier).
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