Power is required to run the shipboard or rig machinery. It is needed on every rig and normally comes from the internal combustion engines usually powered by diesel fuel. A rig may have from two to four engines, mainly depending on how deep the oil well is expected to be drilled. Bigger rigs typically possess three or four 1215 horsepower engines with 1200 kva generators that together may develop 4860 horsepower, or 3624 kilowatts.
The power generated by the engines is then transmitted to the rig components via mechanical or electrical drive. On mechanical rigs, belts, chains, sprockets, or pulleys transmit the power to electric motors at each of the components. Most of the rigs today are electric as they are much simpler to rig up and easier to maintain than mechanical rigs.
The rig power systems use the engines, i.e. prime movers together with the drives to generate and transmit power required for such fundamental activities as hoisting, circulating, and rotating. The rig prime movers convert the energy released by fuel combustion into the energy of motion and force. As noted above, a rig may need 2-4 engines with their aggregate power ranging somewhere between 500 and 5000 horsepower.