Electrical Systems

How power moves through a rig

Generators connect to the main switchboard, which on a dynamically positioned (DP) unit is split into two or more sections by bus-tie breakers. Drilling and thruster drives take power from the board, usually through phase-shifting transformers, and convert it to variable-frequency AC for each motor. Step-down transformers feed motor control centres, lighting and accommodation at 440 V, 230 V or 120 V. The power management system watches generator load and drive demand and limits drive power before the plant overloads.

Choosing between the sub-Categories

Go to Variable frequency drives (VFD) for drive lineups and spare modules. Switchboards and power distribution covers the boards, breakers and transformers. Electrical control systems covers the hardware and software that decide which generators run.

A spare that matches what you already run is mainly a part-number and firmware question. A conversion or a new lineup is an engineering project. It needs a load flow, short-circuit, harmonic and protection study, new cabling and cooling, control integration, and class approval of the modified installation.

Standards across the group

• IEC 61892 covers electrical installations on mobile and fixed offshore units up to 35 kV. Part 5 adds requirements for mobile units, and part 7 covers hazardous areas.
• IEC 60092 covers marine electrical equipment, such as 60092-302 for low-voltage switchgear and 60092-304 for semiconductor converters.
• IEC 62271-200 governs medium-voltage switchgear, and IEC 61439 low-voltage assemblies.
• IEC 60079 and the ATEX directive govern equipment in hazardous zones.
• Class rules such as DNV-OS-D201 and the ABS rules for mobile offshore units add type approval and survey requirements.
• IACS UR E24 limits harmonic voltage distortion on the main busbars to 8% unless the design justifies otherwise.
• IMO MSC.1/Circ.1580 sets the DP guidelines. A change to the power plant on a DP unit needs an updated failure modes and effects analysis (FMEA) and trials.

Integration questions that cut across the group

• Voltage and earthing. Medium-voltage boards usually run with high-resistance earthing. Low-voltage systems are often insulated (IT) with earth fault monitoring.
• Fault level. Every new breaker, drive and busbar must be rated for the prospective short-circuit current at its location.
• Harmonics. Diode and thyristor front ends inject harmonics, which phase-shifting transformers or active front ends reduce.
• Cooling. Liquid-cooled drives need a cooling water circuit and heat exchanger. Air-cooled switch rooms need HVAC capacity.
• Communication. Fieldbus and network protocols must match your drilling control and power management systems.

What matters most when sourcing used

Electrical equipment degrades in storage as well as in service. Capacitors lose condition without voltage, insulation absorbs moisture and contacts corrode. Ask for storage conditions, the date the equipment was last energised and any test reports from then. Obsolescence is the second risk, so check the OEM's lifecycle status for each product family before you commit.

Ask for these records with any used electrical equipment:

• Part numbers, hardware revisions, firmware and software versions
• Class type approval or product certificates
• Single-line diagrams, wiring diagrams and parameter or settings backups
• Factory acceptance and last site test reports
• Storage temperature and humidity history

Plan for the work after delivery too. Drives may need capacitor reforming, switchgear needs breaker and relay tests, and control hardware needs a bench test with your application loaded. Class surveys the installation once it is connected. Naventr lists part numbers, firmware versions and documents as the Seller provides them, so your engineers can check the match.