Wind turbine gearbox lubrication system

Abstract

A wind-turbine gearbox system includes an input gear stage having mating gear surfaces finished to a surface roughness of less than 0.25 micron and at least one bearing supporting the input gear stage. A lubrication circuit is arranged to deliver lubricant to the input gear stage and the bearing during operation of the wind-turbine and includes an inline filter for removal of particles of less than 2 micron from the lubricant prior to delivery. A lubricant for use in the system may have a relatively low viscosity compared to conventional wind turbine gearbox lubricants.

Claims

1. A gearbox system for a wind turbine rated to a capacity of more than 1 MW, comprising: an input gear stage operating at less than 60 rpm and having mating gear surfaces finished to a surface roughness Ra of less than 0.25 micron; at least one bearing supporting the input gear stage; a lubrication circuit arranged to deliver lubricant to the input gear stage and the bearing during operation of the wind-turbine and comprising an inline 2 micron filter; and a quantity of lubricant in the lubrication circuit, the lubricant having an ISO VG of between 100 and 220.

2. The system of claim 1, wherein the lubricant has an ISO VG around 150.

3. The system of claim 1, further comprising a high-speed gear stage, wherein the high speed gear stage comprises mating gear surfaces finished to a surface roughness Ra of less than 0.25 micron.

4. The system of claim 1, further comprising a high-speed bearing, wherein the high speed bearing comprises one or more individual bearings finished to a surface roughness Ra of less than 0.25 micron.

5. The system of claim 1, wherein the wind-turbine gearbox system is rated to a capacity of more than 1.5 MW.

6. The system of claim 1, wherein the lubrication circuit comprises a pump and the inline filter is located on a high-pressure side of the pump.

7. The system of claim 1, wherein the inline filter is a surface filter comprising glass fiber, modified glass fiber, metal, or a polymer.

8. The system claim 1, further comprising an offline filter connected in parallel to the inline filter.

9. The system of claim 1, further comprising a magnetic filter.

10. The system of claim 9, wherein the magnetic filter is located in a sump region of the gearbox.

11. The system of claim 1, wherein the mating gear surfaces are planarized having an average peak to mean height roughness Rpm of 1 micron or less.

12. The system of claim 1, wherein the mating gear surfaces are planarized having an average peak to mean height roughness Rpm of 0.50 micron or less.

13. The system of claim 1, wherein the mating gear surfaces are chemically accelerated vibratory finished surfaces.

14. The system of claim 1, wherein the lubricant comprises more than 85% mineral or synthetic base oil.

15. The system of claim 1, wherein the lubricant comprises more than 95% mineral or synthetic base oil.

16. The system of claim 1, wherein the lubricant comprises more than 99% mineral or synthetic base oil.

17. The system of claim 1, wherein the lubricant is at least substantially free of a defoaming agent.

18. The system of claim 1, wherein the lubricant has a concentration of phosphorous of less than 500 ppm.

19. The system of claim 1, wherein the lubricant has a concentration of phosphorous of less than 10 ppm.

20. The system of claim 1, wherein the lubricant has a concentration of zinc of less than 100 ppm.

21. The system of claim 1, wherein the lubricant has a concentration of zinc of less than 10 ppm.

22. The system according claim 1, wherein the lubricant has a concentration of nitrogen of less than 100 ppm.

23. The system according claim 1, wherein the lubricant has a concentration of nitrogen of less than 10 ppm.

24. The system of claim 1, wherein the lubricant has a concentration of sulphur of less than 20 ppm.

25. The system of claim 1, wherein the lubricant has a concentration of sulphur of less than 5 ppm.

26. The system of claim 1, wherein the lubricant has a concentration of molybdenum of less than 10 ppm.

27. The system of claim 1, wherein the lubricant has a concentration of molybdenum of less than 2 ppm.

28. The system of claim 1, wherein the lubricant has a concentration of boron of less than 10 ppm.

29. The system of claim 1, wherein the lubricant has a concentration of boron of less than 100 ppb.

30. The system of claim 1, wherein the lubricant has a concentration of silicon of less than 10 ppm.

31. The system of claim 1, wherein the lubricant has a concentration of silicon of less than 100 ppb.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The features and advantages of the invention will be appreciated upon reference to the following drawings, in which:

(2) FIG. 1 is a schematic view of a wind turbine operating according to the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

(3) The following is a description of a prophetic embodiment of the invention, given by way of example only and with reference to FIG. 1 which shows a wind turbine 10 comprising a nacelle 12 and a rotor 14. The nacelle 12 houses a gearbox 16 including a low-speed input stage planetary gear 18, a bearing 20 and a high speed gear stage 22. Further intermediate stages may be present (not shown). As will be understood, the design of such a gearbox is relatively complex but is otherwise conventional and its design is largely unrelated to the present invention. Details of the gearbox design may be found in publications such as Recommendation to Comply with the Technical Criteria of the Danish Wind Turbine Certification Scheme Gearboxes, 2007 Danish Energy Authority or the Vestas Mechanical Operating and Maintenance Manual V90-3.0 MW, VCRS 60 Hz, 2007.

(4) In addition to the gearbox 16, the nacelle 12 houses a lubrication circuit 24 comprising an inline pump 26, an inline filter 28 and an oil cooler 30 arranged in series with one another, whereby the inline filter 28 is arranged at a high pressure side of the inline pump 26. The inline filter may consist of one to four or more filters in a parallel arrangement. This arrangement is designed to control the pressure drop between the inlet of the first filter and the outlet of the last filter. In parallel to the lubrication circuit 24 is an offline filter system 32 comprising an offline pump 34, an offline particle filter 36 and an offline water absorption filter 38. A dry air system 40 supplies dry air at an overpressure to the gearbox 16 and a dry air breather 42 communicates with the exterior of the nacelle 12. A magnetic filter 44, is located in a sump region 46 of the gearbox 16.

(5) Unlike conventional gearboxes, the gear elements of the low speed input gear stage 18 have mating surfaces, in particular gear teeth, that are superfinished using an isotropic planarizing technique according to the REM process available from REM Chemicals of Brenham Tex. The resulting surfaces are of mirror-like smoothness having a roughness value Ra of less than about 0.1 micron. Due to the exceptional surface finish, the low speed gear stage is able to operate in mixed or full elasto-hydrodynamic lubrication mode even at the relatively low operational speeds encountered.

(6) The lubrication circuit 24 and gearbox 16 are filled with a quantity of about 200 liters of lubricant as described in further detail below, having an ISO viscosity grade of 150. This lubricant is considered to have adequate viscosity to prevent scuffing and wear in the superfinished low speed gear 18 without being of too high viscosity for the bearing 20 and high speed gear stage 22.

(7) The inline pump 26 circulates the lubricant from the gearbox 16 through the inline filter 28 at a rate of approximately 106 liters per minute. The inline filter 28 is a surface filter a Triboguard Synteg XP or similar from Donaldson Company comprising glass fiber and having a .sub.2[c]1000 based on particles sizes equal to or greater than 2 micron. For such filters, the .sub.x[c] value is defined as the ratio of particles greater than a given size x upstream of the filter to the number of particles of that size downstream of the filter. This means that 99.9% of all particles greater than 2 microns are retained by the filter.

(8) Under normal circumstances, a filter of this caliber would rapidly become clogged with lubricant debris and would exhibit high pressure loss due to the conventional gearbox oils of ISO VG 320. In the present case however it is expected that the inline filter will operate satisfactorily for extended periods. This is due firstly to the reduced debris as a result of the superfinished surfaces. Secondly, the lower viscosity lubricant is more able to circulate freely through the filter.

(9) The filtered lubricant passing out of the inline filter 28 is passed through the oil cooler 30 before being returned to the gearbox 16 where it is delivered directly to the bearing 20 and input gear stage 18.

(10) In addition to the lubrication circuit 24, the offline filter system 32 circulates a relatively smaller volume of lubricant from the gearbox 16 in parallel to the lubrication circuit 24. The offline pump 34 circulates on a continuous basis a quantity of approximately 40 liters per minute at 50 Hertz or 48 liters per minute at 60 Hertz from the sump region 46 and returns the lubricant to the gearbox via the offline particle filter 36 and the offline water absorption filter 38. The offline particle filter 36 is a still finer filter than the inline filter 28 and is calibrated to remove particles below 1 micron. Because it is not in the direct lubrication flow to the critical surfaces of the gears 18, 22 and bearings 20, a possible blockage of the filter would not be catastrophic to operation of the wind turbine 10. Appropriate monitoring (not shown) provides warning to service personnel in the event that such blockage occurs whereby the offline filter component may be changed without otherwise affecting operation of the wind turbine 10.

(11) Offline water absorption filter 38 removes entrained water from the lubricant on a continuous basis. The offline water absorption filter 38 is a depth filter available from C.C. Jensen A/S. The skilled person will readily understand that additional and alternative filter components may be included within the offline system as system requirements dictate.

(12) In addition to air removal by the offline water absorption filter 38, dry air system 40 provides a constant stream of ultra-dry air to the interior of the gearbox. The slight overpressure produced by this supply substantially eliminates atmospheric air ingress to the gearbox via other routes. The dry air breather 42 is a REGEN8 self reactivating dry air breather available from Brownell Ltd, London which actively adsorbs moisture entering the gearbox. When the adsorbent is saturated an automatic reactivation process is initiated which restores the adsorbent to its maximum efficiency level. In order to further protect the interior of the gearbox from external particulates, the dry air breather 42 also includes a 1 micron air filter.

(13) The magnetic filter 44 is generally conventional and is located in the sump area 46 of the gearbox 16 in a position where lubricant is drawn towards the lubricant circuit 24 by action of the inline pump 26. As the lubricant flows past the magnetic filter 44, ferrous debris particles are attracted to and become attached to the magnetic filter 44. Because of the reduced viscosity of the lubricant compared to conventional lubricants, movement of such debris particles is more rapid and the effectiveness of the magnetic filter 44 is increased.

(14) The lubricant used in the above embodiment is produced according to the following example:

(15) The complete lubricant comprises 99.54 percent poly-alpha-olefin (PAO) base oil having a viscosity of ISO VG 150 and a 0.46 weight percent additive package diluted in the base oil. The diluted additive package comprises of 0.030 weight percent zinc di-(heptylphenyl) dithiophosphate antiwear compound that also functions as an anti-micropitting, anti-scuffing and extreme pressure compound, 0.010 weight percent zinc di-(1,3-dimethylbutyl) dithiophosphate extreme pressure compound that also functions as an antiwear, anti-micropitting and anti-scuffing compound, 0.0050 weight percent 2,4,6-tri-tertbutylphenol antioxidant compound. In addition, the diluted lubricant additive package concentrate comprises 0.01 weight percent sodium petroleum sulfonate anti-corrosion or anti-rust compound, 0.3 weight percent non-boron containing polybutenylsuccinimide dispersant compounds and a 0.10 weight percent polyoxyethylene alkyl phenyl ether demulsifier.

(16) Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention.