Interactive monitoring of pitch systems
"A wind turbine is a very complex motion control challenge, because the primary control on the turbine is a pitch system that plays a dual role in both the power output and the key safety function of the turbine," Dennis Webster, director of business development for Moog Inc., told us.
The pitch system is a collection of commonly understood motion control and automation components. This includes an onboard PLC that monitors and controls the system, plus the power electronics, servo drives, and motors that control the motion of the turbine blades.
BLADEcontrol technology from Bosch Rexroth analyzes the natural oscillations of the wind turbine blade. The frequencies of any blade are a unique pattern, like a fingerprint, in the range up to approximately 350Hz.
Webster said the trends in automation are to provide more interactive capabilities to monitor the performance, operation, and efficiencies of these subcomponents. The goal is not to provide a collection of components, but integrated functionality that raises performance and changes how the customer monitors and controls the system.
"With customers in the wind turbine industry, reliability has become a paramount concern. In order to achieve the return on investment necessary, the wind turbine needs to be operating whenever the wind is available," he said. "If you do a Pareto analysis on the reliability of the turbine, the pitch system is often flagged as causing downtime, because it functions as both a control device and a safety device" by serving as the brake for the turbine.
Given this dual role, the information available from the turbine manufacturer can often be incomplete or inadequate for the operator to understand the detailed operating conditions within the turbine. This can impact reliability and the ability to get the system back up and running after any downtime event.
One solution is a single terminal interface for the operation of the motion control components that offers more granularity and insight into what is happening with the pitch system. This information can be used proactively (in terms of preventive maintenance or modifications to the operating parameter set) or to enable advanced troubleshooting. "What we have tried to provide is a window and full visibility into the pitch system, whether the concern is the motion control algorithm or synchronization of the motors and drives," Webster said.
Whether you can get a check depends on which state you are in for home, building size units.
small WT's in the 2-5kw sizes are very cost effective because they can cost less and easily cover the energy needed by an eff home on many cases. A 1500sq' home can easily run on a 2kw WT in average US conditions.
Hydrualics are a joke in this as they are not eff at all mostly under 50% eff, killing them vs 95% eff gears or 100% eff direct drive with no gearing. And a 2Mw radiator to get rid of the waste heat farther adds to the cost.
It's a really interesting idea Cabe. The physical size/diameter of the direct drive generators is typically much larger, but perhaps you keep only the tower and rotor (both very expensive) and replace the entire nacelle. It might work out that the tower fatigue life is close to the 20 year turbine design life even though the ultimate strength is the overriding design factor. It's been a few years since I took a tower design class so I'm not certain about that. Either way I'm sure people would be willing to invest in an upgrade (risking a tower fatigue failure) so long as there was a good value proposition. This assuming in 10-15 years we don't have towers collapsing frequently due to fatigue failures.
A small but large network of turbines is the future? That sounds like a good idea. The question now, can older/smaller/OEM turnbine be upgraded to modern gearless standards? If not, that could be a niche market for expansion.
I am in the industry and there are hydraulic drivetrain concepts and prototype turbines out there. Another touted advantage is putting the electrical generator on the ground. The reason this is not mainstream is the mechanical efficiency losses. A hydraulic drivetrain can peak in the 80's (%) while a gearbox operates above 95% efficiency. There is a lot of talk about gearboxes and failures because there are a lot of geared machines out there, but the industry is moving away from them. Both Siemens and GE (and others) are shipping >3MW direct drive machines these days. Purpose built low speed PM generators are now the most reliable and efficient way to convert wind to electricity.
Oh, and comment about residential turbines: Smaller turbines are more difficult to get a good return on because of their scale but there are midsize turbines (~50kW-500kW) that can provide good ROI in areas that have a decent wind resource coupled with high electricity costs. You can sell power to utilities if your state has a net metering law. google 'net metering' or look on 'windpoweringamerica.gov' to research using wind in your area. These turbines are too large still for the average home/property.
Below is link to web page that illustrates the advantages and approach to using either hydraulics or electromechanical systems for blade pitch control.
http://www.moog.com.cn/english/markets/energy/wind-turbines/blade-pitch-control/comparison-of-electric-hydraulic-blade-pitch-control/
The suppliers are split between offering hydraulic and electromechanical solutions with some companies like Moog offering both. The high power density and simplicity of fluid power keeps it in the game.
It is quite likely that a small portion of the hydraulic fluid from the power transfer lop could indeed be utilized for the other functions of blade pitch control and nacelle rotation. Of course it does come to mind that there are two typs of conditions where that may not work, which are during a shutdown (to avoid storm winds) period of no rotation, and when the wind was so slow that it would not turn the turbine blade. Of course, there could be hydraulic accumulators to provide backup for a while, and there could also be a backup pump running from auxilliary power. Other than that, there is no immeadiately obvious reason why not.
Now that the concept is published, perhaps some organization could run with it.
My understanding is that the utility company will not pay you any money. they will give you credit for future energy usage. But they will not actually send you a check. Therefore, you can only save what you would spend for each month. You can't actually make any money with an at home windmill. I don't know if this is still factual but it came from a reliable source at one time.
I read an article about some different people who put up private windmills on their property for their own personal use and even with the cost savings on energy it was going to take nearly 20 years to pay it off. I think until energy prices go way up it takes a long life for some of these green ideas to pay off.
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