If power is lost to a DPS-controlled drill-ship’s thrusters there is a risk that the rig will drift off its position, which can potentially give rise to huge impacts and the risk of damage to the subsea equipment (Blow Out Preventer (BOP), Riser, and associated equipment). Along with such an unfortunate occurance also will come significant financial impacts; the cost of repairs, new equipment and lost day rates. Clearly, in the event of a power loss, the speed of engine re-start is of critical important.
Drill-ship building scene: Photo courtesy of Maersk Drilling
Since 2011 Maersk Drilling has invested USD 4.5 billion in seven new drilling units; three ultra harsh environment jack-ups at Keppel FELS in Singapore and four ultra deepwater drill-ships at Samsung Heavy Industries in South Korea. In the design of the drill-ships’ electrical propulsion system, Maersk say that their engineers, set the engine emergency start-up time bar higher, looking for a decrease in the usual 30-40 second blackout start-up time. In response engine designer MAN Diesel & Turbo in Germany, the licensee Doosan (which is building the engines), Samsung and ABB (generator manufacturer) put their heads together and delivered: the modified engine is now able to re-start in less than 10 seconds, more precisely, in just 8.5 seconds. How was this achieved?
Drillship image backdrop & technicians: Photo courtesy of Maersk Drilling
Fast Emergency Start-up
The fast start mode (only to be activated during emergency situations) was obtained by optimising and tuning the existing engine systems, that is, the turbochargers, jet assist system, starting air system, governor control system and the AVR (Automatic Voltage Regulator) of the generator.
As a result of these modifications, the engines’ optimum now matched the generator output. This was achieved by de-rating the engines and introducing smaller turbochargers, which has improved the load step performance (the ability to take up load quickly), and this will result in improved performance of the MMC (Multi Machine Control) mode during drilling operations.
As an important spin-off from the work done, decreased fuel oil consumption during low-load operations will result in a yearly fuel saving of circa 5.3% compared with a standard engine set-up.
Interestingly, according to Maersk Drilling, the modified engines now meet the starting-time requirements for an emergency generator at a nuclear power plant.