Fullerton Toroid C.V. Transmission Design
Fullerton Design has an extensive history in the concept of Toroid CV Transmissions covering over forty years, exhibited by the Analysis Report from Stanford Research Institute (S.R.I.) dated November 09, 1971, as well as the first Toroid Patent, filed by Robert Fullerton, #3,727,474 and granted April 17, 1973.
Fullerton Design II is, here, addressing two key issues that the wind power industry faces as it matures: moving offshore and the use of bigger turbines. However, the clear focus must be on system reliability as well as environmental acceptance, which have become the number one design challenge that wind turbines must address.
In addition to a technology focus on gearboxes and generators suppliers are looking at the entire drive train and how to use technologies such as gearbox health management tools, condition monitoring, ac brushless servo motors, and precision cooling systems to provide robustness, as well as serviceability that the next generation of this alternative energy demands.
Instead of focusing solely on the gearbox, as in the past, Fullerton Design II is focusing on the complete electromechanical drive train business unit. If we look at the wind turbine drive train, from where the rotor shaft connects to the gearbox and on the other side where electrical energy comes out of the turbine, there are tremendous opportunities for boosting system reliability and serviceability while improving environmental impact.
Fullerton Design II turbine design engineers are now taking a pragmatic approach on the need for reliability and serviceability in the drive train of offshore wind turbines. The focus is on larger wind turbines (4, 5, 7, and up, to 10 Mega Watts) developed for offshore operation and on ways to keep the drive train stable; by deploying optimum conditioning and cooling for the various key components such as bearing, gearbox, generator and converter.
It is a well-known fact that if the bearings and Toroid Units are well-lubricated, cooled with clean oil, have no moisture or humidity present, and employ a good filtration package the Toroid Unit is less likely to fail. By monitoring the Toroid Unit using a new patentable concept of condition monitoring package (Fig. 1 )that includes trends from temperature, pressures, vibration, cleanliness of the oil, and moisture issues we can reliably predict failure, or prevent failures, by knowing what will happen in the Toroid Unit over a time horizon.
With the trend moving toward larger turbines and offshore applications because of the availability, and consistency, of the wind an important focus will be on the serviceability and service intervals of these offshore installations. This is driving suppliers to better control of the temperatures in the now used gearbox and to the optimization; as well as monitoring of the cleanliness of the oil in the system. To get service people on board, in an offshore turbine, it normally means you need a ship or helicopter. As a result the suppliers are improving the lubrication systems and increasing the lifetime of the filters, so it has a maximum of once a year to service the unit; and sometimes the service interval is increased to 18 months.
Users can employ an online connection to assess when they need to schedule maintenance on the turbines. Some of these systems constantly measure the pressure differential over the filter element and communicate the information over industry-standard electronic protocols that can be accessed remotely. With ability to program these devices, reaching a threshold of pressure level indicates when it is time to change the element. Remote monitoring also allows for preventative and scheduled maintenance events that reduce the cost of service. Not a problem with the Fullerton Toroid Unit.
Fullerton Design II will also offer systems to monitor the condition, as well as the temperatures, of the Toroid Unit lube oil with respect to the amount and type of possible contamination in the bearings or Toroid Unit. If everything is running smoothly, and there is no extensive wear on the bearings, it is normally OK to use an 18-month service interval but, performance is also dependent on the Toroid Unit itself, vibration, alignment, loads and other factors.
Fullerton Design II introduced modularity into the system. So instead of using one large filter we are specifying two or three optimum size and mesh filters outboard filter/cooler units (Fig. 2) to the Toroid Unit lubricating system to better perform service and further condition the oil while keeping pressures consistently low in the system. The lifetime of the components is vital along with serviceability. It is known that, in many gearboxes, people are using a lot of connectors and hoses to connect different components, which, means there is always a possibility for leakage; not to mention the drop in efficiency of the package. This is eliminated in the Fullerton Concept.
Fullerton Design's approach to these applications is to integrate multiple functions into a patented uni-package, which combines the process and the control parts of the total system, plus optional functions including bypass filtration if that is needed (Fig. 3).
A third important area is condition monitoring. Normally, if there is any oil condition monitoring at all in these systems, it is metal residue monitoring - which means that only the large metal particles are monitored; not for size but for count.
We know that if it produces a lot of smaller particles, before the big particles start to appear, a system is starting to degenerate. By automatically measuring particles, that are 100 microns or larger, we will start trending micrometer-sized particles, which the human eye can't see. When the selected amount of particle contamination is reached an electrical connection is automatically made; providing notice of mechanical metal wear. With the systems used today you almost need dedicated laboratory equipment to view particles of this size this is eliminated with the Fullerton Design II Micron electrical switch (Fig. 4).
Fullerton Design II will introduce new tools for this type of monitoring and develop a system to do this online with the Toroid Unit without taking samples to a lab. The key is that measurements can be trended on a continuous basis and specific commands can be used to prevent further damage or optimize the use of the filtration system.
Trend to AC Brushless Servo Motors
The key in wind turbine applications is reliability and availability, which means the wind turbine must be available to produce energy whenever there is wind. The challenge for the Fullerton Design II system is to make sure that components are reliable and robust enough to support that environment, which means balancing features, performance, and cost while providing a system that is, for all intents, invisible to the public as well as being non offensive to the environment.
Electric pitch control systems are typically located in the rotating part of the turbine (hub) and include one rotary actuator (electric motor and gearbox) connected to each blade. Power and control electronics allow the motors to develop the right torque and follow a motion profile provided by the turbine controller. A power back-up system allows the motors to bring the blades into a safe position, even in case of power loss, and a set of encoders (one per blade) supplies blade position feedback. This also is not necessary, in the Fullerton Concept, of providing a simpler mechanical device.
With wind turbine applications, whether they are offshore or not, the environment is harsh because system components are essentially outdoors within a hub that is not weatherproof. Ambient operating temperatures range from extremes of -40 to 50C. This means that the actuators and motors need special attention paid to sealing, and the ability to meet performance requirements throughout the full temperature range. Again not required in this Fullerton Concept.
The rigorous environmental conditions on the concepts in use today apply to the controls as well, plus all of the components in the control cabinet. Up in the moving rotor as well, the system must be designed to withstand the vibration and shock of it being continuously rotated. Reliability is key, because the motion system functions as the key safety system of the wind turbine. Not a concern with this Fullerton Design II Concept.
The concepts in use today all focus on supplying highly reliable integrated electric pitch systems to the wind industry. Even though they will offer pitch systems, using different types of motor technologies (dc brush type motors, ac induction motors and ac brushless servo motors), the focus is on systems using alternating current brushless servomotors.
Traditionally, dc motors have been applied to pitch systems but, there is a current trend to applying more ac synchronous motors to eliminate the brush failure mode. Throughout the rest of industry, and aerospace applications, there is a general belief that ac motors are inherently more reliable, even though they haven't been widely accepted in the wind industry yet; a problem not associated with the Fullerton Concept.
Differential Gearboxes
The trend in the wind industry we have seen is a continuing move toward larger-size turbines. Until last year, the most common size installed in the U.S. was 1.5 megawatts. But, the trend is larger and larger systems and turbines in the 2 to 2.5 megawatt range will be more or less a standard for onshore wind turbines over the next several years. The larger units now in service as well as on the design board only emphasize the claims of the critical environmentalist whereas the Fullerton Design II Toroid Unit will overcome this visual blight by not being visible.
"The concept that Fullerton Design II is targeting is multi-megawatt turbines. It is slender and compact, due to its CVT Toroid design concept with two planetary stages."
A clear trend is more systems going offshore, or actually "near shore", where they are typically installed between three to five miles off the coast. The advantage is a smooth flow of wind, the turbine is not in anybody's backyard, and the noise issue is gone. For all those reasons, wind turbines are moving to offshore locations, but a major problem is regular periodic maintenance which has the potential to become prohibitively expensive; this is overcome with the Fullerton Design Toroid Unit.
Because of quality, and reliability issues, people are talking about using a direct drive system rather than a gearbox for large offshore applications, says Gupta. We see some benefits in that but, by the same token, with developments to increase reliability and improved quality, we believe you can have a very good solution with a Toroid Unit in the system even up to 5 or 6 megawatts using the constant motion of the wave action providing an efficient, silent, usage.
With the demand for higher power density and compactness growing, Fullerton Design's Toroid Unit offers more compact drives and minimizes the weight by providing a multiple power-split Toroid Unit design solution with out the danger of "blade collision" with human or wild life.
Unlike conventional generator gearboxes in the multi-megawatt class four, or more, planetary gears do not revolve around the sun wheel in the input stage. Instead, the Fullerton Design II concept offers two input stages, each fitted with three planetary toroidal rollers sandwiched between two toroid disks, and the advantages of a static determination paired with freely adjustable sun pinions; providing a continuous current flow with out concern of wind velocity.
Another key design feature is a thin outer diameter, with only a slightly greater total length. With turbine capacities increasing, it offers up to a 15 percent weight advantage over gearbox concepts currently in use without a decrease in reliability.
There have been tremendous improvements, in terms of planning and doing preventative maintenance rather than repairs after a catastrophic failure. Along with the trend toward larger turbines, typically located offshore, there is a rise in condition monitoring solutions that enable users to predict, and plan for maintenance.
Lubrication is the key to the reliability and operating life of gearboxes and this applies in particular to gearboxes for wind energy plants, due to the difficult conditions in which they operate. This is why Fullerton Design II is offering main gearboxes featuring their own cooling lubrication system with particle monitoring and water content sensors.
While engineers are generally concerned about the reliability of the gearboxes, often what actually limits bearing life is lubricating fluid, or oil, which becomes too dirty or too hot. The push to condition monitoring is one way to manage these important assets.
We believe we have eliminated most, if not all, of these concerns.