Ricardo MultiLife - Bearing Innovation
The MultiLife is an innovative bearing-saver for wind turbines that prolongs the life of the critical fixed inner-race of planet bearings within the gearbox and other bearings operating in the same way. It achieves this by a compact and retro-fittable system to manage rotation of the fixed race.
Ricardo was established in 1915. They specialize in delivering engineering and technology programs for the global automotive, transportation, defense, and energy industries. Today the company is represented in 16 locations across the world with more than 1,500 employees – including over 1,300 technically qualified and engineering staff. Among its great achievements are the development of the world’s fastest diesel engine for the record breaking JCB DieselMax car (350 mph), development and manufacture of the dual-clutch gearbox & drivetrain for the Bugatti Veyron, and the improved fuel economy for the Voyager aircraft enabling it to fly around the world without refueling.
Politicians, utilities, and technicians: Everybody agrees that the Cost of Energy (CoE) from offshore wind must be reduced. OceanWise takes a closer look at how the drivetrain can be improved with solutions that fit into both new and existing wind turbines.
By Anne Korsgaard
Drivetrain design innovation is a focus area both for producers and subcontractors in the wind energy sector. And with emerging technologies in drivetrains, including direct drive, hybrids and medium speed, the market is becoming increasingly mature and at the same time more complex for the sub-suppliers.Everybody agrees that smart innovation is the way forward to reduce the Cost of Energy. But how do companies identify where development money should best be spent?
- Firstly, our focus extends from the blade bearing in the hub, where the loads enter the drivetrain, through to the electrical output from the transformer, and down through the main bearings and main frame to the yaw bearing and yaw system. All of these systems are interlinked by torque or power flows or load paths. These areas between them have a big part to play in determining future offshore CoE. They are the most challenging areas in achieving the up-scaling that is required, and improvements in cost per MW and reliability will also be a significant opportunity, explains Project Director for Clean Energy at Ricardo, Giles Hundleby.
The third generation of the Multilife design. It has a mechanism that moves the normally fixed inner race thus making the distribution of loads onto the bearing more even. Illustration: Ricardo
Retro-fitted components assure flexibility
One focus area is to develop improved and flexible solutions that can be of use in existing wind farms across the world when parts need changing. And at Ricardo they do not just develop solutions for new wind turbines – the aim is to develop and produce technologies that can be used both in new turbines and for upgrading already commissioned wind turbines. The overall mantra is to achieve higher reliability and optimized drive train design with modular solutions.
-The first step in this process is to identify the large potential cost savers in the industry, says Giles Hundleby, and states that for Ricardo, amongst others, three areas are of special interest when talking about reducing the Cost of Energy: 1. Load sharing and bearing innovation, 2. Torque limiting and decoupling, and 3. Monitoring systems.
Challenge #1: Planet gears and bearings - load sharing and bearing innovation
One great challenge is the failure in the planet gears and bearing systems within the gear box. This is a key area of damage and failure in some drivetrains and costs large sums in Operation and Maintenance (O&M) every year. Solving this problem is a large potential money saver.
- Among other things we have analyzed bearings that have been changed due to failure, and have found that in part the problem is caused by unequal load-sharing across all the planets, unfavorable loading on the planet bearings, and the fixed design of normal planet pins focusing wear in one area. Wind turbine bearings with fixed inner races are wearing in a 40 degree arc (see illustration), thereby causing premature failure when compared to the design life.
- Our innovations in these areas are aimed at sharing planet gear loads more equally and making them act through the bearings in a more favorable way in order to increase life. We achieve this by a compact and retro-fittable system to manage rotation of the fixed race, explains Giles Hundleby.
It is a major advantage in the design that the bearings can be retrofitted and only small changes to the gearbox are required as a refurbishment option for existing wind turbines.
Challenge #2: Torque limiting and de-coupling
Another major challenge for the wind industry is the cost tied-up in the drivetrain to deal with aspects of the torque and other loads in excess of the ideal operating loads, and the failures when these loads are either not designed for or dealt with effectively. Ricardo aspires to solve the problem:
-Using a device to eliminate all off-axis forces and moments except pure torque, will mean that the gearbox and rest of the drivetrain only has to contend with the driving loads. It will operate in a much more benign environment, and will not need to be designed to cope with these other loads, that cause additional (and time-varying) distortions and mis-alignments. Gearboxes and drivetrains are also designed for significant overload torque capability, which adds to weight and cost. These torque overload cases are usually highly dynamic, which adds further potential damage to the drivetrain. Ricardo is working on torque truncation technologies that means the maximum torque a drivetrain will see is known and the design can be optimized for a lower maximum, saving weight and cost, explains Giles Hundleby.
Challenge #3: Condition monitoring systems and development – operation & maintenance
According to the Megawind report (2010) from the Danish Wind Industry Association, O&M costs account for approximately 18% of the total cost of ownership in a 20 year lifecycle of an offshore wind farm. Better monitoring systems will make it easier to make the right decisions in order to avoid superfluous visits to the offshore wind farm. Better monitoring will simplify the assessment of when a component has to be changed in order to avoid break-down and costly stand-still time.
Giles Hundleby explains the Ricardo philosophy:
- With the very high cost of offshore O&M, it is becoming crucially important to know the health of the drivetrain and be better able to predict the remaining useful life under normal operating conditions. There is also the opportunity to extend the remaining useful life by adapting the control parameters to reduce the type of conditions that will cause an early stage failure to propagate quickly. Ricardo is in particular investigating advanced sensors including acoustic and oil film sensors to support both the development of the prognostic algorithms and sensing of in-operation conditions and early-stages of failure. By better design of monitoring and development of prognostics tools in the drivetrain development stage, better management of any O&M requirements can be achieved, for example by the converging of multiple turbines O&M requirements to the same future weather window. This is why we spend a lot of development effort on this technology.