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Electrical Control Systems
Electrical Control Systems covers the power management system, generator control and protection units, synchronisers, load-sharing controllers and the PLCs and I/O behind them. These decide which generators run, how load is shared and what the plant does after a fault or blackout. Most used and surplus demand here is for spare modules for discontinued systems, and for complete systems in a reactivation.
What the power management system does
The power management system (PMS) starts and stops generators against load and keeps spinning reserve. It shares active and reactive load between sets and sheds non-essential consumers before an overload trips the plant. On a drilling unit it also limits the power drilling drives and thrusters may draw. Fast load reduction cuts drive power within milliseconds when a generator trips. After a blackout the PMS restarts sets, closes breakers and reconnects consumers in a set order.
Configurations
- Generator controllers from makers such as DEIF and Woodward handle synchronising, load sharing and generator protection at each set.
- A PLC-based PMS runs plant-level logic on dual redundant controllers. Siemens, ABB and Rockwell families are common.
- Integrated vessel automation systems, such as Kongsberg's, combine PMS, alarm monitoring and control.
- Drilling drive systems carry their own power limiting that links to the PMS.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Controller family and revision | Sets spare and software compatibility | Part number, hardware revision |
| Generators and sections supported | Must cover your plant | Number of sets, bus-ties |
| Redundancy | Required for DP notations | Single, dual, triple |
| Network and protocol | Must match drives and automation | Profibus, Modbus, Ethernet |
| Software version and licence | Decides whether it will run | Version, licence key |
| Approval | Decides class acceptance | Type approval, DP notation |
Standards and approvals
IEC 60092-504 and IEC 61892 set requirements for control and instrumentation on offshore units. DNV-OS-D202 and the ABS rules for mobile offshore units cover automation, safety and control systems. IACS UR E22 classifies computer-based systems by consequence of failure and sets software and change-management rules. On a DP unit, IMO MSC.1/Circ.1580 and the class DP rules make the PMS part of the redundancy design. Any change needs an updated FMEA and proving trials, including blackout recovery tests.
Failure modes and inspection
Hardware rarely wears out. The usual causes of failure are:
- Corroded connectors and terminals from humid or salt air.
- Dried electrolytic capacitors in power supplies.
- Flat or swollen backup batteries that lose the program on power-down.
- Cracked solder joints from vibration and heat cycling.
- Failed fans and blocked filters in panels.
Testing means powering hardware on a bench, checking that it boots, loading the application and exercising I/O. Full functional testing of PMS logic needs the vessel's own system, a hardware-in-the-loop simulator or the OEM's test bench. Blackout recovery and fast load reduction are proved only during trials on board.
Documentation
- Part numbers, hardware revisions and firmware versions for every module
- Application software backup, configuration files and licence keys
- Functional design specification and I/O lists
- Class type approval and the last DP FMEA and trials report, where relevant
- Change log of software modifications
Integration and compatibility
A spare module must match the hardware revision your firmware supports. A replacement controller may need a newer firmware that your engineering tools cannot read. Check the network protocol to drives, switchgear relays and the vessel automation. Check governor and AVR interfaces at each generator, whether analogue, digital or fieldbus. Changing one generator controller can alter load-sharing behaviour across the plant, so retest parallel operation.
Spares, upgrades and lifecycle
Many offshore PMS installations still run on discontinued PLC families, such as Siemens S5 and Allen-Bradley PLC-5. Used and unused surplus modules are often the only spares left. Buy modules that you can test, and buy the program backup with them. For a whole system on a DP unit, an OEM upgrade usually costs less in trials and approval than piecing together used parts. Related equipment is under Switchboards and power distribution, Automation systems and DP control systems.
FAQ
Frequently asked questions
Where can I find spare parts for a discontinued rig power management system?
Used and unused surplus modules from stacked or scrapped units are the main source once the OEM stops supplying a product family. Match part numbers, hardware revisions and firmware exactly, and make sure you hold the application program before relying on a spare.
What does fast load reduction do on a drilling rig?
Fast load reduction cuts drilling drive and thruster power within milliseconds when a generator trips, so the remaining sets are not overloaded and the board stays live. The PMS or drive system sends the reduction signal directly to the drives.
Can I swap a used PLC module into my PMS?
Usually, if it has the same part number and hardware revision and runs your firmware. Bench test it before installation. On a DP unit, check whether class treats the swap as a modification that needs FMEA review or trials.
What is IACS UR E22 and does it affect used control hardware?
IACS UR E22 sets requirements for computer-based systems on board, including categories by consequence of failure and rules for software changes. A used module running an approved software version is a like-for-like spare. A new software version or system may need fresh class review.
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