The technology focus for wind turbine operators is squarely on refining operating efficiencies and minimizing downtime -- in pursuit of the ultimate goal of a 20-year design life. By providing a window into the details surrounding the operation of the gearbox and turbine blades, automation and motion control is at the forefront of the technology push.
Conditioning monitoring is the new buzz phrase as automation and control suppliers work with turbine operators to maximize system performance and develop tools for remote software troubleshooting and diagnostics.
The 20-year design life target
"The key issue in terms of new technology for wind turbines is increased reliability, which automatically leads to the need for conditioning monitoring and a process for taking preventive actions," Parveen Gupta, regional vice president of renewable energy for Bosch Rexroth, told us. "One way to increase reliability is to have a continuous indication of operating conditions and the ability to take corrective or preventive actions based on the conditions."
New Remote Terminal software from Moog offers remote access, real-time operational monitoring, and troubleshooting for the pitch system of a wind turbine. The software helps users diagnose potential operational issues in the pitch system and take corrective actions.
In terms of reliability, the target design life for gearboxes used in wind turbines is 20 years. But operators in the field are finding that gearboxes typically need major repairs or replacement in five to seven years. Replacing the gearbox means both a significant cost and downtime for the turbine owner.
If the operator can monitor the turbine's condition and performance, it makes it possible to reduce downtime by identifying damage and developing plans to minimize the time required for a gearbox replacement. In some cases, if the damage is caught early, it can be repaired without replacing the gearbox. The overall focus on reliability and condition monitoring is a way for operators to guarantee investments will perform effectively over the long haul.
"We are developing new products and testing them with selected wind turbine OEMs in the areas of both blade and gearbox condition monitoring," Gupta said. "Blade conditioning monitoring is aimed at detecting problems such as an ice deposit or a crack in the blade."
Most of the focus has been on integrated systems (both hardware and software). Hardware includes RTDs that are installed in the gearbox and sensors that can be embedded into the wind turbine blades to sense additional deflection or added weight. The software constantly monitors these functions and interprets the data to decide when to take corrective action. With blades that are cracked, for example, it's possible for the system to check for different vibrations or frequency responses. This type of monitoring might be integrated into a package for end customers to upgrade the monitoring capabilities of turbines in the field.
I haven't studied wind turbine design in any depth, but the idea of a hydraulic transmission sounds brilliant to me. Sort of analagous to the automatic transmissions in cars instead of manual, I suppose. Efficiency should be good, but the maintenance, nacelle design, etc. should all be greatly simplified. It would be interesting to have someone in the industry comment on why this path hasn't been taken.
The trasmission is a high-wear and quite heavy device, and presently it is the one item that has a definite lifetime. In addition, it takes up a fair amount of space and the connection to both prop and generator must be quite precisely aligned. REplacing the gearbox in the upper assembly is a very big deal task. The generator, generator controls, gearbox, and gearbox cooling hardware comprise more than half the weight of the upper end, and so moving all of them to ground level would produce quite a savings in space and weight. An added advantage of the hydraulic approach is that all of the cooling could be located on the ground, since cooled oil would also cool the topside pump assembly. The piping losses can be minimized using techniques that have been well known in the hydraulics industry for many years. The somewhat reduced efficiency of using hydraulics would certainly be offset by the increased reliability and the reduced servicing costs associated with having much of the system at ground level.
Using ground hydraulics is an interesting approach and I believe the reason it hasn't been tried would be the losses in moving all that fluid such a great distance. Up top you would still need something to control the blade pitch and positioning, so you may as well have the transmission up there too.
The challenge with low speed alternators and generators is that they need a whole lot of poles to be "low speed". Each time the number of poles doubles the speed iscut in half, and to get to a 600 RPM synchronous speed one is already up to 16 poles. That winds up being a large device. Putting the generator on the ground allows for whatever speed and number of poles is convenient. Plus, the added advantage of being able to adjust the ratio almost instantly is a handy side benefit.
There does exist an alternative for putting the gearbox and the generator up in the nacele where they are very hard to get to and expensive to service. The solution is to have the turbine directly driving a large variable displacement hydraulic pump, and then use a variable displacement hydraulic motor to turn the generator down on the ground. This wold avoid using a gearbox and also allow generation of power at lower wind speeds, with the added advantage of being able to run the generator at whatever speed was desired. The generator and associated support and control equipment would be at ground level, making them cheaper to install, maintain, and repair, and the power would already be at ground level, making the grid connectionssimpler. Moving the weight down to the ground would reduce the required strength for the base and support, so that would add to the savings. One more potential advantage is that hydraulics does offer a way to store energy in an accumulator, which could potentially assist in a method of longer term energy storage.
What I don't understand is why this approach has not been used very much so far.
- rate life isn't the primary metric... it's return on investment (ROI). Life span has an impact, but so long as it is not different that expected, it remains just one of several variables impacting ROI.
- already (6 years ago) designed in processing power for monitoring the vibration with active pitch control for minimizing wear on the minimal transmission involved. (4 generators around one large gear - balanced torque on frame, made easier generator swap out inside nacelle - no crane or helicopters involved). Amazing to "listen" to difference in the system with high freq adjustments being made vs without any active control. The basic controls already have the maintenance monitoring , data logging, high level access across networks, etc. to minimize costs.
- Pitch is constantly changing based on location of blade in a single rotation. Why? because on really large diam systems, the speed of wind is significantly different at the top of the arc vs the bottom of the arc.
- smaller systems? Great, but they will always have some significant disadvantages to big systems. a- closer to the ground (slower wind speeds and near birds of prey food source) b- higher blade speeds (noise/bird strike) c- distributed maintenance over larger area (higher maintenance per watt) d- majority of population does not have a reasonable location for installation (limited urban options) e- most people will not want to take responsibility for their own power source (most don't want to be responsible for their own plumbing!) .
In many locations it can make sense... but for majority of population in US and Europe, it isn't an option. Centralized power (and all of it's weaknesses) is likely to be with us for a long while. And yes, this will waste power in distribution and be a major cost in maintenance of transmission lines.
I wish it wasn't so.,,. (in general, I prefer de-centralized systems)
Regardless, the real changes in this industry will come when all the energy sources operation on a "level" playing field, not because of 50 year product lives. It is amazing to see the gov incentives still being paid out to oil/gas .. while many alternative energy incentives have dried up.
A few points. In the future there will be no gearboxes cutting that expensive part and problem. They will be replaced by larger diameter generators with many more poles instead. GE already is doing it on their new units.
You can't look at a composite part and know if it's ok as delaminations and other problems have little to no visual effect until near fairlure. But a simple microphone can in real time at low cost. To actually find the problem Xray, Ultrasound or other tech is needed though tapping with a hammer can by someone who knows how.
The biggest problem are these huge WT's are really investment vehicles generating loans, commissions, units profits with generating power as a nessasary byproduct.
The real future in WT's are small home, build size units that make/save retail electric cost instead of wholesale electricity thus 2-3x's more cost effective.
WT's scale well into the .5kw size units though studying it a 2kw/16' dia size for most homes can supply their needs in many places.
Another is smaller local wind farms close to the demand as transmission lines for lrager, distant ones can cost as much as the wind farm does!!
They have always said 20 yr life but that has not proven anywhere near tue mostly because they keep increasing size thus don't have time to optimise designs before they are an 'obsolete size'.
Yet many small units from the 30's are still going strong!! A decent WT should have a 30-50 yr life simply to cut maintaince costs.
If 20 years is the current focus, what was the product lifetime rating in the past? I suspect much lower.
With the Siemens 6MW turbine, the current world's largest (dec 2012), I would want a 20 year life at the very least. The 8MW Vestas, set for 2015, will be even larger. I say bump the life to 30 years, then we'll have something.
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