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Electrical Power Transmission

On diesel-electric rigs, powerful diesel engines drive large electric generators.
The generators, in turn, produce electricity that flows through cables to electric
switch and control equipment enclosed in a control cabinet.
This engine-generator set is one of three on this rig.
From the control gear, electricity goes through more cables to electric motors.
The manufacturer attaches the motors directly to the equipment to be driven – for
example, the draw- works or mud pumps.
The diesel-electric system has a number of advantages over the mechanical
system. The diesel-electric system eliminates all the heavy and fairly complicated
machinery making up the compound. Because an electric rig does not require a
compound, crew members do not have to spend time lining up and connecting the
compound with the engines and drawworks. Also, on an electric land rig, the rig
designer can position the engines well away from the rig floor so that crew members
enjoy less engine noise. On mechanical rigs, the compound-to-engine set up requires
that the engines be placed close to the rig floor.

HOISTING SYSTEM
Whether mechanical or diesel-electric, a rig's job is to drill a hole; to do this job

it must have a hoisting system. A typical hoisting system is made up of the
drawworks(or hoist), a mast or derrick, the crown block, the traveling block, and the
wire rope drilling line.

The Drawworks
The drawworks is a big, heavy piece of machinery. It consists of a revolving
drum around which crew members wrap or spool wire rope drilling line. It also has a
catshaft on which the catheads are mounted. Further, it has clutches and chain-and-
gear drives so that the driller can change its speed and direction. A main brake
provides the driller a way of slowing and stopping the drum. An auxiliary electric
brake assists the main brake by absorbing the momentum created by the load being
raised or lowered. Big electromagnets inside the auxiliary brake oppose the turning
forces on the drum and help the main brake stop the load.

The Cathead

A cathead is a winch, or windlass, on which a line, such as rope, cable, or chain
is coiled. When activated, a cathead reels in the line with great force. Pulling on a
line is vital to screwing and unscrewing (making up and breaking out) drill pipe.
Typically, four catheads are mounted on the catshaft of the drawworks, two on each
end. On the very ends of the catshaft are friction catheads. Right next to them are the
automatic or mechanical catheads.
A friction cathead is a steel spool a foot (30 centimetres) or so in diameter. It
revolves as the catshaft revolves. In the old days, crew members employed friction

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