Sailing with generator units in parallel operation in a closed bus power plant is more efficient and sustainable, but increases the risk of malfunctions. According to Bakker Sliedrecht, its in-house developed class approved generator protection system deals with this issue.
This is of great importance for diesel-electric vessels in the offshore with a dynamic positioning system (DP) where blackouts are out of the question. But also for dual-fuel ships, where sailing on both gas and diesel sometimes leads to failures in the fuel supply.
Many DP vessels have divided their power plant’s generators and switchboards into different independent isles. The advantage of such an open bus system is that each isle has its own protection. In case of malfunctions, a “sick” isle does not affect other isles. So if a diesel generator does not function properly, for example due to an electrical, mechanical, control or fuel problem, the “healthy” generators will continue to operate.
This prevents the entire power plant from becoming unstable, which would cause a blackout that shuts down the power supply of the vessel. Communication problems between diesel generator sets can also cause blackouts. However, the disadvantages of an open bus system are that fuel consumption is relatively high and thus, emissions are also higher.
Common Diesel Generator Protection system
That is why nowadays ships prefer to sail with a closed bus or ring system with generators in parallel operation, allowing generators to be switched off or on when needed. This leads to more efficient use of diesel generators, fuel savings and less environmental impact. However, safety and reliability are essential with a closed bus system, because otherwise a faulty generator will affect the components of the power plant that are functioning properly.
Bakker Sliedrecht has developed the Common Diesel Generator Protection system to guarantee this safety and reliability. The system detects electrical problems with the generators as well as problems with the diesel engine or fuel supply.
‘It is actually an addition to the security that is already in the generators and switchboards. With parallel operating diesel generators, you often do not immediately know which component is the cause of the malfunction. This system uses software to rapidly detect which defective component is the cause and switch it off immediately to prevent the entire power plant from being dragged into a blackout,’ explains Paul Bracké, who has worked on developing CDG protection for several years.
Protection of power plant reliability
Power plant protection of power plant reliability is very important, especially for offshore work vessels that construct, dismantle or service oil platforms and wind farms. These vessels use a dynamic positioning system (DP2 or 3) to maintain their position at all times. Therefore, a malfunction should never lead to a blackout of the power plant, causing the thrusters to shut down and the ship to get out of its position. This can lead to major damage or other problems.
An open bus system is the safest in those situations, but as previously mentioned, it is not efficient and sustainable. ‘Working near the piles of an oil platform or wind turbine can be dangerous, so failure of the power plant can never be an option,’ says Bracké.
First classification of dual-fuel DP2 vessel
Bakker Sliedrecht has now succeeded in this. In the past year, the system has been extensively tested on a large crane vessel with four generators of ten megawatts each, which will be deployed in the construction of wind farms. Because the ship’s power plant is equipped with dual-fuel generators, the challenge was extra complex.
Bracké: ‘CDG Protection is intended for all ships with a closed bus power plant, but for dual-fuel vessels there is another important aspect to be regarded. The dynamic behaviour of a diesel engine is different when it runs on gas. This results in a higher dynamic load on the power plant and there are potentially more fuel problems as a result of the much more complex installation.’
Without generator protection, the crane vessel would not receive a classification to operate in DP2 closed ring mode. After various computer simulations, the CDG Protection was successfully tested in a pilot set-up of four generators. The system was subsequently approved by DNV-GL for on-board installation. The crane vessel is now the first dual-fuel DP2 vessel with a generator protection system that has been classified.
High detection and reaction speed
Bakker Sliedrecht decided to develop the necessary knowledge for its own CDG Protection system in 2011. First as a feasibility study, which later developed into a full-fledged development project.
‘Large suppliers have also developed similar systems, but only supply them as an option with a complete power plant. The advantage of Bakker Sliedrecht’s CDG Protection is high detection and reaction speed. Our system has proven to be fast enough to interpret dynamic phenomena in power distribution due to fuel differences or fuel switching,’ says Bracké.
CDG Protection will also be applied in a light version to some multi-purpose vessels.
‘This protection is mandatory for DP vessels which sail with a closed bus system. On other ships, the crew must determine what to do in case of a failure or deviant behaviour. Then it depends on how alert they are,’ says Bracké. ‘Our system is developed for all ships where you don’t want a blackout to occur. CDG Protection can help crews to detect problems and malfunctions in the power plant faster and better.’
He concludes: ‘In the future, if ships start sailing autonomously and remotely operated, besides navigation, the safety and reliability of the power plant will become more important. Then the system can be of use for remote diagnostics.’