Power system is a one of the most important part of drilling rig because it is needed to power up all drilling rig systems (rotary, circulating, hoisting, blow out preventer and monitoring systems etc.)Depending on rig horse power, there can be three or four engine Generator set. All these engines run on diesel fuel and mechanical power produced by diesel engine is used to run generator, these generators convert mechanical energy given by diesel engine to electricity. This electricity produced by all these engine generator set is given to power distribution system; power distribution system can be SCR or VFD.
SCR mean silicon controlled rectifier.
VFD mean variable frequency drive.
SCR is used in case of direct current.Whereas VFD is used for AC or alternating current.
Normally most of drilling rig have VFD power system for TDS, whereas rest of rig main equipment like mud pump, drawworks and rotary table take have DC motors and take power from SCR power system.