A consortium secured a contract from a National Oil Company for the refurbishment and conversion of their Offshore Oil rig from a Mobile Offshore Drilling Unit (MODU) to a Mobile Offshore Production Unit (MOPU).

The oil drilling jack-up rig has independent leg cantilever jacks. Since the rig came for overhauling, its onboard power was not available for jack-up and other operations. A typical 3 leg jack-up rig consists of 3 jacking legs and a jetting pump.

Each jacking leg consists of 1 motors, generally rated up to 20 kW which start simultaneously. The leg jetting pump runs the hydraulic auxiliaries while the jacking motor operates simultaneously to extend (jack) the leg for anchoring.

As all the legs must move instantaneously, its essential to start respective motors at the exact same time. Typically, these motors are rated 600v/ 60 Hz. As the rig had to be taken in and out of water for maintenance activity when there is a high draft of sea-water and taking tides into account, any rig movement needed to be planned based on high draft calculations during high tide situation, with typically two high tides every 24 hours.

So, the timing plays an important role in docking and de-docking the rig. The operation of legs extending downwards is similar to lowering the load during hoist operations due to the inertia the motor tends to act as a induction generator, and feed power back to the system. Also, if legs are sucked in sea mud it may create reverse power. So a reliable system to absorb this regenerative load during jack-up operation is crucial.

PDOC needed a reliable power partner who was up to the challenge and able to meet the stringent QHSE standards of this world class modern shipyard infrastructure facility.