As part of a general overhaul, Siemens Energy has equipped two drilling platforms owned by Transocean of Houston, Texas, the largest offshore drilling company in the world, with a reliable, high availability power supply. The new system based on the direct current network link Siplink replaces the former power supply for the drilling platform drive units. The Siemens solution not only increases the reliability and availability of the drive units but also offers savings of up to a third of the fuel costs for the diesel generators accompanied by a reduction in CO2 emissions. Generator maintenance costs can also be cut because the generators can run at a considerably more effective operating point controlled via a fail-safe energy bus.

Offshore drilling platforms and drilling ships need a reliable power supply for their drive units. In order to fulfill their function, drilling platforms have to be able to be maneuvered exactly in position, with their up to eight thruster motors, not only against the wind and wave action but also against the torque of the drilling drive unit. If the electric power supply were to fail there would be a risk of the drill pipe breaking within a very short time, causing repairs costs amounting to millions. The offshore drilling company commissioned Siemens to develop a new power supply system that would increase the availability of the power supply system for the thruster drive units of Transocean’s Sedco 702 and Sedco 706 drilling platforms and thus reduce operating costs.


Siemens developed a solution for the two drilling platforms based on Siplink (Siemens Multifunctional Power Link), a flexible direct current (DC) network link in which two converters are interconnected by a DC link and are each connected to two independent power networks. In this way Siplink connects the two 11-kV medium voltage subnetworks on board the drilling platforms via the DC link. If a fault occurs in one of the two subnetworks, the DC link ensures that the drive units are supplied with power from the other 11-kV subnetwork. The power requirement of both medium voltage subnetworks is measured continuously in all operating states and the load flow is automatically optimized. A fail safe energy bus (FSE) performs this function for each DC subnetwork.

If a fault occurred in the previous power supply system for the thruster drive units, all the drive units supplied by the 11-kV subnetwork concerned failed. Because of the high inrush currents in the converters, the motors could not be switched back on simultaneously but only in sequence, which could lead to the drilling platform drifting off position if this took too long. With the new system thanks to control via FSE bus all drive units remain in operation even if one of the two 11-kV subnetworks should fail.

The power supply solution for the drive units using Siplink also allows substantial fuel savings accompanied by lower CO2 emissions. Up to 30 percent of fuel costs can be saved because the diesel generators which feed power into both networks can now be run at a considerably more effective operating point. This means that one diesel generator in each subnetwork is sufficient in a calm sea, whereas in the past two always ran in parallel. The other generators are only switched in when the sea is rough or in case of higher requirements. Formerly three diesel generators in each subnetwork used to supply power to the thruster motors. Two generators always had to be run simultaneously to provide a fail-safe supply even if their output was not needed at that particular moment. Last but not least, the Siplink solution cuts maintenance costs for the diesel generators because they can run at a significantly more favorable operating point, and not as before in the lower partial load range where they are subject to high wear.