1、New Guidelines for Wind Turbine Gearboxes by: Robert L. Errichello, GEARTECH and Brian McNiff, McNiff Light Industry TECHNICAL PAPER COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services STD-AGMA 97FTMB-ENGL 1997 m Ob87575 0005327 24b m New Guidelines for W
2、ind Turbine Gearboxes Robert L. Errichello, GEARTECH and Brian McNiff, McNiff Light Industry The statements and opinions contained herein are those of the author and should not be construed as an official action or opinion of the American Gear Manufacturers Association. Abstract The American Gear Ma
3、nufacturers Association in cooperation with the American Wind Energy Association has recently published AGWAWEA 921-A97, Recommended Practices for Design and Specification of Gearboxes for Wind Turbine Generazor Systems. Much has been learned about the unique operation and severe loading of wind tur
4、bine gearboxes since the early 1980s. AGMAAWEA 921-A97 provides guidelines that incorporate this knowledge to help ensure reliable gearboxes for wind turbine service. It gives valuable information to gear manufacturers, wind turbine designers, operators and manufacturers. The document provides infor
5、mation on wind turbine architecture, environmental considerations, gearbox loads, gearbox design, procurement specification, manufacturing, quality assurance, lubrication, operation and maintenance. Copyright CZ 1997 American Gear Manufacturers Association 1500 King Street, Suite 201 Alexandria, Vir
6、ginia, 22314 November, 1997 ISBN: 1-55589-702-9 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSTD-AGMA 77FTM8-ENGL 1777 Ob87575 0005328 182 W NEW GUIDELINES FOR WIND TURBINE GEARBOXES Robert L. Emchello Gear Consultant GEARTECH Townsend, Montana Bria
7、n McNiff Wind Energy Consultant McNiff Light Industry Blue Hill, Maine INTRODUCTION The wind turbine industry has been plagued with gearbox failures, which cause repair costs, legal expenses, lost energy production, and environmental pollution. A wind turbine gearbox is considered failed if it: Jams
8、 and stops rotating. Breaks and allows the rotor to tum without tuming the generator. Exceeds allowable sound level or vibration limit. Has excessive oil leakage. Requires excessive maintenance. Failed gears, shafts, keys, bearings, and housings have caused jamming or breaking. Bending fatigue is us
9、ually the ultimate failure mode when geahoxes jam or break. However, bending fatigue is often a secondary failure mode initiated by other failure modes such as macropitting or scuffing. Some wind turbines were destroyed when gearboxes broke and allowed rotors to overspeed. Strict sound regulations i
10、n the United States and Europe required shutdown of noisy tuhines because failed gears or bearings caused excessive sound or vibration. Failed shafts, seals, and housings caused excessive oil leakage and, in some cases, total loss of lubricant and gearbox failure. Less severe leakage increased maint
11、enance and costs. Soil contamination required costly cleanup. Three years ago, a group of individuals dedicated to wind power recognized that many gearbox failures were due to a lack of undemanding of the severity of the wind-turbine-operating environment. They sought to define this environment and
12、improve communication between gear and wind turbine manufadurers so reliable gearboxes could be obtained. Therefore, the American Gear Manufacturers Association (AGMA) and the American Wind Energy Association (AWEA) formed a committee of wind turbine manufacturers and operators, researchers, consult
13、ants, and gear and lubricant manufacturers. The committee developed AGWAWEA 921-A97, Recommended Practices for Design and Specification of Gearboxes for Wind Turbine Generator Systems.“ The document reflects latest knowledge about wind loads and failures, plus insights of gear and wind-turbine manuf
14、acturers and operators. It desuibes wind-turbine configurations, operating conditions, and environmental fadors that affect gearbox life. It offers guidelines for defining wind loads, and specifying gears, bearings, operation, and maintenance. All of these guidelines focus on one goal: ensuring reli
15、able wind-tuttine gearboxes. 1 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesSTD-AGMA 97FTM-ENGL I777 = b87575 5327 017 D WIND TURBINE CONFIGURATION AND OP E RAT1 ON Two wind turbines with the same generator can experience extremely different gearbox
16、 loads. A good control system maximizes energy capture and minimizes structural loads. AGWAWEA 921 describes common wind turbines and the significance of their architecture and operation on gearbox loads. Rotors can be either horizontal, as in a horizontal- axis wind turbine (HAWT); or vertical, as
17、in a vertical-axis wind turbine (VAWT). Some HAWS are integrated systems where the gearbox supports the rotor, and in some cases the generator and other components such as yaw drives. Wfih this configuration, the gearbox housing must transmit rotor loads to the supporting tower without incumng exces
18、sive &;esses or defiedions. Integrated systems require communication between the wind turbine designer and gear manufadurer to properly design interfaces. By contrast, a modular system consists of a rotor, rotor support shaft and bearings. gearbox, and generator, each mounted to a common support pia
19、te. In this case, the gearbox doesnt need to support extemal loads. Rotor toque is controlled by adjusting blade pitch (adive control), or by aerodynamic stall (passive control). Adive control increases gearbox complexity because, in many cases, the mechanical, eledrical, or hydraulic control passes
20、 through a hollow gearbox shaft to blade actuators. Passive control is simpler but creates higher peak toques than active control. ENVIRONMENTAL CONSIDERATIONS Wind turbines must withstand aggressive environments ranging from hot, dusty deserts to cokl. wet marine environments. Temperatures can vary
21、 widely, which affects lubrication. The oil sump temperature should be at least 5% above the lubricant pour point during start-up, and less than 95oC during operation. Otherwise, heaters or coolers may be necessary. All sites requin? highcapadty, filtered breathers and positive shaft seals to contro
22、l contamination. Desiccant breathers minimize water contamination. Protective coatings help prevent cornsion. DEFINING GEARBOX LOADS Many early wind-turbine geahoxes failed because designers were uncertain of loads such as: Long periods of small oscillation when the brake stops the high-speed shaft
23、and the wind buffets the rotor. Long periods of low speed and light loads during light winds. 0 Long periods of high speed and light loads when winds are below cut-in speed. High transient loads when the generator conne they may cause gear misalignment and high bearing loads. LU 8 RI CATI ON Micropi
24、tting, maaopitiing. adhesion, scuffing, abrasion, and other lubrication-related failures are widespmad in wind tuhine gearboxes. To avoid such failures, the lubrication system should provide an adequate amount of cool, dean, and dry lubricant to gears and bearings. Pressure-fed systems should have a
25、 filter to clean the oil, and can have a heat exchanger to cool the oil. Maintenance and condition monitoring should be considered at the design stage. Many factors need to be considered when seleding a lubricant, including viscosity, viswstty index, pour point, additives, micropitting resistance, s
26、cuffing resistance, and cost. There are debates on relative advantages of synthetic versus mineral oils, especially regarding micropitting resistance. Operators have leamed that experiments are required to find acceptable lubricants. Wind turbine gears have relatively low pitch line velouty (typical
27、ly 1-10 ms) and high loads (contad stress over 1400 MPa). These conditions require synthetic or mineral gear oil with antiscuff additives and the highest practical viscosity (at least IS0 VG 320). Too low a viscosity causes micropitting, macropitting, adhesive wear, and scuffing. Micropitting is pre
28、valent in windturbine gearboxes. Though it does not always lead to catastrophic failure, it generally reduces gear tooth accuracy, increases noise, and can progress to full-scale macropitting and gear failure. To prevent micropitting, maximize specific film thickness by using gears with smooth tooth
29、 surfaces and an adequate amount of cool, clean, and dry lubricant of the highest viscosity permissible. You may need to tiy different lubricants to find one with adequate micropitting resistance. FVA project number 54 l is a standardized test for micropitting resistance of lubricants. A ten-stage p
30、ass is minimum acceptable performance. Running-in gears under controlled loads reduces tooth surface roughness and risks of micropitting and scuffing. However, manufacturers and purchasers disagree on who should perform this task. Gear manufacturers are reludant to run-in gears because their test fa
31、cilities are limited; and purchasers are reluctant because they cant always control loads. Therefore, run-in must be negotiated between the gear manufacturer and purchaser. 4 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling ServicesQUALITY ASSURANCE The purchas
32、er should write a procurement specification for wind-turbine gearboxes that fully describes the appiication, load spectrum, and minimum requirements for design, manufaduring, quality assurance, testing, and gearbox performance. The gear manufadurer should prepare plans for quality assurance, inspedi
33、ons, and tests. The purchaser should confirm that the gear manufacturer understands all requirements of the procurement specification before awarding the contrad. Criteria for judging gear manufacturer competence are design review meetings, evaluations of manufaduring and QA pians, and visits to man
34、ufaduring facilities. To compare competing gearbox designs, AGMAIAWEA 921 recommends these Standards for rating the components: Gearbox: ANWAGMA 6001, ANSI/AGMB 6010 or ANSVAGMA 6023. Gears: ANSIIAGMA 2001. Bearings: ANSVAFBMA Standard 11. Shafts and keys: ANSIIAGMA 6001. Manufaduring plans should c
35、learly define all acceptance mena before manufaduring starts. After awarding the contrad, the purchaser should audit manufaduring, inspedion, and testing for conformance to the procurement specification. it is best to qualify prototype gearboxes before manufaduring produdion gearboxes. Prototype gea
36、rboxes should not be manufactured until the purchaser approves all elements of first article inspedions and tests. After prototypes have met the requirements of the procurement specification, and manufaduring plans are sound, the transition to produdion should be straightforward. OPERATION AND MAINT
37、ENANCE b87575 0005332 b03 and micropitting, and prolong gear and bearing lives. A gearbox inspedion program assures reliable operation. Inspedions should be done at run-in and at regular intervals. AGMAIAWEA 921 gives guidelines for on-site monitoring and laboratory analyses of lubricants for viscos
38、ity, water content, acid number, solid contaminants, and additive depletion. it also describes methods for monitoring vibration and temperature. Safety is a major concern for wind turtine operators because of the risk of falling, being trapped in rotating components, and being injured while maneuver
39、ing in restrided spaces. Gearboxes should have an adequate number of steps, handholds, and lanyard hook points. Housings should have rounded comers, and all exposed rotating components should have safety guards. Because access is difficult and workspace is limited, design the gearbox to ease mainten
40、ance. CONCLUSIONS AGWAWEA 921 provides valuable information that enhances communication between purchasers, manufadurers, and operators of wind turbine geaitmxes. 0 Reliable gearboxes for Wind turbine service can be obtained by following the guidelines of AGMAIAWEA 921. REFERENCES 1. FVA-Infomation
41、Sheet Micropitting, No. %/i (July, 1993) Forschungsvereinigung Antriebstechnik e.V., Lyoner Strasse 18, D-60528 FrankfuNMain. The gear manufadurer, lubricant supplier, and purchaser should estabiish plans for start-up, operation, and maintenance, before gearboxes are placed in service. Geamxes should be run-in under controlled loads to reduce the risk of swffing 5 COPYRIGHT American Gear Manufacturers Association, Inc.Licensed by Information Handling Services
