How To Design A Wind Turbine Gearbox?

Insuring wind power generation has been scrutinized by insurance companies. Insurers entered the fast-growing market in the 1990s, before wind turbine durability and long-term maintenance requirements were completely understood. To accommodate the demand, a number of units were put into service with just limited prototype testing.

Failures during wind turbine operation were widespread during the period of rapid introduction rate. Rotor blades shedding fragments, short circuits, damaged foundations, and gearbox failure were among the problems. Unreliable wind turbine gearboxes stemmed from a severe miscalculation of operational loads and intrinsic gearbox design flaws prior to the creation of a set of internationally recognized wind turbine gearbox design standards.

The failure to account for all important design loads, the non-linearity or unpredictability of load transfer between the drive train and its mounting fixture, and the mismatched reliability of individual gearbox components were all highlighted as causes.

According to reports, the German Allianz received 1,000 wind turbine damage claims in 2006. A facility operator had to expect damage every 4-5 years, discounting malfunctions and uninsured breakdowns.

Insurers adopted measures requiring the operator to include maintenance requirements in their insurance contracts as a result of previous failures. Over the wind turbine’s 20-year design life, one of the most common maintenance requirements is to replace the gearbox every 5 years. This is a costly undertaking, as gearbox replacement accounts for around 10% of the wind turbine’s building and installation costs, and will have a negative impact on the expected revenue from a wind turbine (Kaiser & Frhlingsdorf, 2007). Figure 1 shows the dimensions of a Liberty 2.5 MW wind turbine’s Quantum Drive gearbox (Clipper Windpower, 2010)

The failure of wind turbine gearboxes can be traced back to the wind’s unpredictable gusty nature. Even the tiniest gust of wind will cause uneven loading on the rotor blades, causing torque on the rotor shaft to load the bearings unevenly and misalign the teeth of the gears. This misalignment of the gears causes uneven tooth wear, which facilitates further misalignment, which causes even more uneven wear, and so on in a positive feedback loop.

A one- or two-stage planetary gearing system, also known as an epicyclic gearing system, is used in the majority of wind turbine gearboxes in the 1.5 MW rated power range. Multiple exterior gears, or planets, revolve around a single center gear, the sun, in this design. An outside ring, also known as an annulus, is necessary to adjust the rpm.

The annulus in Fig. 2 would be connected to the rotor hub, while the solar gear would be attached to the generator of a wind turbine. Modern gearboxes, on the other hand, are far more intricate than those shown in Fig. 2, and Fig. 3 shows two separate General Electric (GE) wind turbine gears.

Planetary gearing systems have a higher power density than parallel axis gears, and they can provide a wide range of gearing possibilities as well as a substantial change in rpm in a small space. Planetary gearing systems have a number of drawbacks, including the requirement for sophisticated designs, the general inaccessibility of critical components, and heavy stresses on shaft bearings. In wind turbine applications, the last of these three has shown to be the most problematic.

The number of teeth, N, that each of the three component gears has is the first step in calculating the reduction potential of a planetary gear system. These are the values that will be used:

What is the best way to design a gearbox?

The selection of material is the initial step in the gearbox design process. The attributes of various materials must be thoroughly researched before a material is chosen. A material must be chosen based on a variety of factors such as strength, weight, durability, cost, and other factors.

What is the optimal wind turbine gear ratio?

In a wind turbine, a gearbox is used to transfer rotational speed from a low-speed rotor to a higher-speed electrical generator. With a rate of 16.7 rpm input from the rotor to 1,500 rpm output for the generator, a usual ratio is around 90:1. A gearbox is not required in certain multimegawatt wind turbines. The generator rotor spins at the same speed as the turbine rotor in these so-called direct-drive machines. This necessitates the use of a huge and costly generator. Other wind turbines on the market have gearbox ratios of around 30:1, obviating the need for the maximum speed stage in a normal gearbox. There is a trade-off between the cost of slower, higher torque generators and the durability of gearboxes and gear stages.

In a wind turbine, how does the gearbox work?

The blades of typical gearbox-operated wind turbines rotate a shaft that is connected to the generator through a gearbox. The gearbox translates the blades’ rotational speed15 to 20 rotations per minute for a 1 MW turbineinto the 1,800 rotations per minute required by the generator to produce power.

Due to wind turbulence, the many wheels and bearings in a gearbox are subjected to extreme stress, and any flaw in a single component might bring the turbine to a standstill. As a result, the gearbox is the most high-maintenance component of a turbine. Offshore turbine gearboxes are more fragile than onshore turbine gearboxes due to higher wind speeds.

The removal of the gearbox from the wind turbine reduces the machine’s most technically difficult component, enhancing reliability. However, there are two drawbacks to adopting direct drive instead of a gearbox system: expense and weight.

Until recently, Felker noted, a wind turbine system with a gearbox was less expensive than one without because of the cost savings that came from having a higher-speed generator.

However, over the last two years, it has been proved that direct-drive machines are not always heavier or more expensive than geared systems, according to Siemens’ Stiesdal. Two technological breakthroughs have created this fluctuation: the cost of permanent magnets used in direct drives has decreased dramatically, and the generator arrangement has become more streamlined.

Direct drive conversion from coil-driven to permanent magnet systems has been critical in lowering costs. Magnetic systems are not only lighter, but they also require less copper, which has seen a price surge since early 2010. According to Parthiv Amin, president of Northern Power Systems’ community wind division, “the reduction in weight witnessed by direct-drive machines is actually leading to a fall in expenses, especially in terms of manufacturing costs.”

Direct-drive systems have also become more economical because to changes in the generator. Northern Power Systems, for example, has improved the efficiency of the transition from the permanent magnet generator to the full power converter and then to the grid in its systems. According to Amin, losses from power conversion using Northern Power’s 100 kW wind turbine are less than 2%.

In its 4 MW direct drive units, GE has included a permanent magnet generator with a 6-meter diameter. For greater reliability than the preceding generation, the two main bearings transfer axial and bending loads from the rotor to the bedplate.

In addition, Siemens has made a tweak to the generator. The rotors of direct-drive machines were previously housed inside the system. The rotor is now on the outside of the machine, according to Siemens.

“The rotor on our machine is just a thin-walled pipe with permanent magnets,” Stiesdal explained. “There’s only 20 millimeters of magnet and 50 millimeters of steel tubing outside the air gap.”

Wind turbine makers, according to Felker, are driving the market for direct-drive machines. “Clearly, some significant progress has been achieved, otherwise there wouldn’t be so many direct drive computers on the market.”

Siemens hopes to unveil its 6 MW direct-drive prototype later this year as a benchmark, making it one of the world’s largest permanent magnet machines.

“When it becomes accessible in big numbers four to five years from now, we expect that to be a game-changing machine,” Stiesdal said. Because of its resilience and low maintenance requirements, the 6 MW machine is projected to prove popular with offshore wind farms, according to Stiesdal. “I estimate that all offshore machines from 6 MW and up will be supplied with direct drive in ten years.”

The first ScanWind direct drive unit has been in operation for more than five years at GE’s offshore test site in Hundhammerfiellet, Norway. GE installed 13 of the units at the test site in 2005. According to Milissa Rocker, worldwide communications manager wind for GE Power & Water, those turbines have collected the equivalent of 50 years of experience under some difficult conditions.

On the Norwegian coast, Scanwind (recently acquired by GE) wind turbines are in operation. GE provided the image.

The success of these test units prompted GE to design its next-generation wind turbine, a 4 MW machine that is the company’s largest wind turbine. The superior drive train and control technologies acquired by GE through the acquisition of ScanWind will be used in this turbine.

Onshore, direct-drive systems are also in use. Northern Power Systems began deploying direct-drive systems in Alaskan villages near the Bering Sea in 2001, working with local utilities to enhance the cost effectiveness of powering isolated communities. “Because the communities were not mechanically skilled to repair equipment like gearboxes,” Amin explained, “the goal was to make it maintenance-free.”

One argument for using direct drive machines instead of gearboxes in distant settlements, according to Amin, is that they require less maintenance. Unlike most gearboxes, which require maintenance such as oil changes every six months, Amin claims that a Northern Power direct drive system will only require “annual inspection and lubrication in its first five years.”

The company already operates 39 permanent magnet direct-drive turbines with a capacity of 100 kW in many isolated Alaskan villages. According to Amin, the median availability of the company’s turbines placed worldwide is 98.7%, compared to 93 to 95 percent for a standard wind farm. In Europe and the United States, Northern Power Systems has sold over 200 direct drive machines.

While enhancements have been made to vehicles that are currently on the market, more testing is being done to boost direct drive even more. A dynamometer facility at NREL is where a generator is tested to see how well it performs in various wind conditions. Northern Power Systems is currently testing a 2.2 MW generator at the site.

MathWorks, a provider of model-based design software for engineers and scientists, is also working to improve direct drive systems. Simulink and Matlab, two MathWorks tools, can model a specific control system to adapt to changing wind direction and speed. MathWorks offers an approach to implementing direct-drive design by generating code and creating “real-time prototypes,” as the firm describes them.

“These solutions enable you to create a system-level design of your turbine system, as well as a multi-domain view to control the algorithms,” stated marketing manager Tony Lennon.

This software enables for direct drive simulation, which can lead to more precise power conversion. “Because the systems are so expensive, whatever you can do in the simulation process to make the proper size choice saves a lot of money,” Lennon explained.

Wind turbines have how many gears?

A wind turbine’s gearbox is made up of three gears. The largest gear, which has 1,260 teeth, is meshing with the second gear, which has 70 teeth. The 70-tooth gear is then meshed to the 14-tooth final gear.

What is the weight of a wind turbine gearbox?

The gearbox takes up 5 to 15% of the nacelle’s space, weighs several tons, and accounts for 20 to 30% of the turbine’s total cost. No gear system is 100 percent efficient; around one percent of the power is lost at each gear step, as a rule of thumb.

How do you figure out the gearbox?

In a transmission, the gear ratio is the ratio of the rotational speeds of two meshing gears.

Because each gear has a different diameter, when both axes are engaged, they rotate at separate speeds. Changing the gear ratio is the same as changing the torque being applied.

Divide the output speed by the input speed (i= Ws/ We) or divide the number of teeth on the driving gear by the number of teeth on the driven gear (i= Ze/ Zs) to get the gear ratio.

Advantages of geared transmissions

When compared to other types of transmissions, geared gearboxes provide a number of advantages. First, they provide excellent force and motion transmission capabilities, as well as a long service life and high reliability.

But it’s the incredible precision of their gear ratio that sets them apart, allowing them to be used in precise manufacturing.

Gear ratios in geared transmissions are extremely exact, making them ideal for precision machinery.

Unlike other mechanisms such as chains or pulleys, they are tiny in size, allowing them to be used in both small and large equipment and spaces, as well as in difficult-to-reach locations.

Furthermore, geared transmissions are one of the most often used systems in major industries such as automotive due to its ease of maintenance.

What are the gearbox specifications?

1) REQUIREMENTS TECHNICAL AND GENERAL: a) The gearbox must be of the double helical kind. It is not acceptable to have a split gear wheel. b) At a distance of 1 meter, the maximum permitted noise level should be less than 85 dB(A). c) The gearbox must be capable of withstanding 20% overspeed for a minimum of five (5) minutes.

What factors are taken into account when constructing a gearbox?

Technical and non-technical requirements, as well as legal and regulatory as well as commercial factors, are all part of a gearbox design program. The process begins with a detailed description and understanding of the type of gear or gearbox required, as well as the nature of the application: what type of machine it will be used in, where and how it will be used, and what performance characteristics are expected. The target price and volume (total number of units required and per year) are also crucial considerations. The next step is to establish who owns the final design: the customer or the service provider/consultant.

  • If multi-speed, the overall gear ratio, as well as the number of separate reductions and their gear ratios, as well as the ratio tolerance.
  • Expected duty cycle for unit, either provided by customer or calculated by customer and service provider/consultant. This is made up of a set of torque, speed, and percent-of-time numbers that are representative of what the unit is likely to encounter in the field. It may be necessary to instrument a working machine and record torques and speeds in order to develop this.
  • The torque peaks and spikes in the system: smooth and continuous or peaks and spikes in torque.
  • The primary mover’s description and characteristics are as follows: Consider an electric motor with a torque and performance curve that produces 50 horsepower at 3,600 rpm.
  • Life requirements, either a weighted average value calculated according to Miner’s rule for this duty cycle or a different value for one or more particular situations.
  • Agreement on the methodology for calculating gear stress and life, as well as the necessary standards and governing bodies, such as AGMA 2001, ISO 6336, or DIN.
  • Dependability is expressed as a percentage or number of failures per 100, for as 99 percent reliability or one failure per 100.
  • If relevant, design failure mode effects and analysis (DFMEA) or design reviews are required for product verification.
  • Who is responsible for executing product validation tests, and what are the approval criteria?

Following that, qualitative and subjective client desires, such as low noise, light weight, smooth operation, high dependability, good serviceability, and low cost, should be considered and documented.

The scope of the project can then be documented in a Statement of Work. It should be signed by both the customer and the service provider/consultant to ensure that everyone is on the same page about the work to be done.

At this point, the service provider/consultant can start working on the gear or gearbox system’s basic design and engineering. Preliminary engineering calculations and the construction of a concept layout schematic depicting the gearbox’s original configuration are included. Gear data, stress and life estimates, and other gearbox component choices and calculations, such as bearings, shafts, splines, and fasteners, are all included in these engineering calculations. The buyer can then be given an initial preliminary design specification that includes:

  • Preliminary design calculations, including gear stress and life analysis and findings, are included in the concept layout drawing.

A product design verification strategy can be chosen by the service provider/consultant utilizing one of the following methods: third-party assessment, alternative calculations, or comparison analysis to previous successful designs.

Throughout this process, there will most likely be several design reviews, some of which can be attended by both the customer and the provider. A concept or initial design review, design validation and verification review, manufacturing design review, critical design review, and final design review are all examples of these types of reviews. The consumer may request a DFMEA, or the service provider/consultant may initiate one.

This process may go through numerous iterations as the customer and service provider/consultant work together to arrive at a good and final design, which is then frozen. After that, the customer gives his or her final consent to proceed with the final design elements.

The design and analytical work is completed by the service provider/consultant. The following design outputs are prepared and presented:

  • An assembly design with balloons and item numbers that correlate to the bill of materials, showing cross-section views of the gearbox.
  • Individual part drawings can be provided if it is established that the buyer will own this design.

A prototype gearbox can be constructed, assembled, and tested after the design is complete and all information has been sent to the customer. To guarantee that the product satisfies the design requirements and is satisfactory, product testing and validation comments should be supplied to the service provider/consultant.

What is the formula for calculating gearbox ratio?

In a gear train, the gear ratio is the ratio of the input gear circumference to the output gear circumference. The gear ratio aids in estimating how many teeth each gear has to achieve the necessary output speed/angular velocity, or torque.

The gear ratio between two gears is calculated by dividing the input gear’s circumference by the output gear’s circumference. The circumference of a given gear can be calculated similarly to the circumference of a circle. It looks like this in equation form:

When only the diameters or radii of the gears are examined, we can derive the gear ratio using the following equation:

Similarly, the number of teeth on the input and output gears can be used to derive the gear ratio. It’s similar to thinking about the circumferences of the gears. The circumference of a gear can be calculated by multiplying the sum of a tooth’s thickness and the distance between teeth by the gear’s number of teeth:

gear ratio = (number of input gear teeth * (gear thickness + teeth spacing)) / (number of output gear teeth * (gear thickness + teeth spacing))

However, because the thickness and spacing of the gear train’s teeth must be the same for the gears to engage smoothly, we can eliminate the gear thickness and teeth spacing multiplier from the equation above, leaving us with the following solution:

  • a fraction or a quotient in which the numerator and denominator are divided by their largest common factor to simplify the fraction.
  • a decimal number – expressing the gear ratio as a decimal number provides a rapid estimate of how far the input gear must be moved for the output gear to complete one full rotation.
  • 2:5 or 1:14 are examples of ordered pairs of numbers separated by a colon. We can see how few spins are needed for both the input and output gears to return to their original positions at the same time.

From a different angle, we may calculate the mechanical advantage (or disadvantage) of our gear train or gear system by taking the reciprocal of the gear ratio in fractional form and simplifying it to a decimal integer.