Power Generation

How a rig's power plant is arranged

Most drilling units built since the 1990s are diesel-electric. Three to eight gensets run in parallel on the main switchboard, and the power management system starts and stops them as load changes. Jack-ups and older semi-submersibles mostly run high-speed engines. Drillships and large semi-submersibles more often run medium-speed engines feeding an 11 kV or 6.6 kV board. Older SCR rigs generate at 600 V AC and rectify it to DC for the drilling motors.

The emergency set sits outside the main machinery spaces with its own switchboard. It carries the emergency services when the main plant is lost and must not depend on any system in the main engine room.

Choosing between the sub-Categories

Main diesel engines matter most when your alternator is sound and the engine is worn or obsolete. Generators cover a failed winding or a spare alternator for a fleet on one frame size. Emergency power systems follow separate SOLAS and MODU Code rules and are rarely interchangeable with a main set.

A complete genset on its common base frame removes three engineering tasks at once. The coupling, the shaft alignment and the torsional vibration calculation were done for that pair. Splitting an engine from its alternator, or pairing two makes, means class wants a new torsional calculation before it approves the set.

Rules that apply across the group

MARPOL Annex VI applies to drilling units, because MARPOL counts fixed and floating platforms as ships. Regulation 13 limits NOx from diesel engines above 130 kW (174 hp) by tier.

A replacement engine that is identical to the one removed keeps its original tier. A non-identical replacement counts as a major conversion and must meet the tier in force on the date of replacement. Engines used solely for emergencies are outside Regulation 13. Regulation 3.3 also exempts engines solely dedicated to exploration and exploitation of seabed resources. Gensets that also power thrusters and accommodation rarely fit that wording, so get your flag Administration's view in writing before relying on it.

SOLAS chapter II-1 and the IMO MODU Code set the main and emergency power requirements. IEC 61892 governs electrical installations on mobile and fixed offshore units, and IEC 60092 covers the equipment standards for alternators, switchgear and converters. Class societies such as DNV and ABS issue product certificates at manufacture and survey the installation.

Integration questions to settle first

• Frequency and speed. A 60 Hz board needs 1,800, 1,200, 900 or 720 rpm with the matching pole count. A 50 Hz board needs 1,500, 1,000 or 750 rpm.
• Fault level. Adding a genset raises the prospective short-circuit current, which must stay within the rating of every breaker and busbar.
• Load sharing. The governor and automatic voltage regulator must talk to your power management system, or you need new controllers.
• Fuel. SOLAS II-2 requires fuel with a flash point of at least 60°C (140°F) for main engines and 43°C (109°F) for emergency generators.
• Hazardous areas. Any engine near a hazardous zone needs air intake shut-off, spark-arrested exhaust and surface temperature control.

What separates a good used genset from a bad one

Hours since the last major overhaul, the overhaul report and trended oil and insulation results say more than total hours. A set preserved with oil fogging, desiccant and anti-condensation heating can be in better shape than one that ran on light load for years. An unused set from a cancelled newbuild carries the NOx tier of its build date, which may limit where you can fit it. Naventr writes up each set from the Seller's data plates and records and can arrange a third-party inspection on request.