Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 1 Motivation to design and build a wind turbine gear unit with plain bearings • The reliability of roller bearing solutions is under discussion • „White Etching Crack (WEC)“ is a failure mode occurring in roller bearings used in wind turbine gear boxes, for already more than 20 years. Damage is typically seen in early stages of operation and can occur on different bearing positions. Damages are seen on almost all bearing designs. • Until today the root cause is not established. A number of theories have been developed but none of these theories is proven yet. • Plain bearing solutions are known as reliable solutions in many industrial applications. • There is a strong demand in the wind market to test plain bearings with the aim to increase wind turbine gearbox reliability. 21 Aus Wissenschaft und Forschung * Dipl.- Ing. Dirk-Olaf Leimann ZF Wind Power, Lommel, Belgium Plain Bearing Lubrication in Wind Turbine Gearboxes D.-O. Leimann* Eingereicht: 26. 10. 2016 Nach Begutachtung angenommen: 15. 12. 2016 Heutige Getriebe für Windkraftwerke im Leistungsbereich zwischen 2 und 8 MW haben mindestens eine Planetenstufe und eine Stirnradstufe. Die Verzahnungen sind in der Regel einsatzgehärtet und die Lagerung der Planeten und Wellen erfolgt durch Wälzlager. Durch Schäden an den Wälzlagern in Winkraftgetrieben, die auch als White Etching Cracks bezeichnet werden, hat ZF Windpower etwa 2010 damit begonnen den Einsatz von Gleitlagern als alternative Lösung zu untersuchen. Hierzu wurde ein erster Prototyp im Jahre 2011 gebaut und 2012 intensiv getestet. Die wichtigen Fragen in der Konstruktion waren, welche Anforderungen stellt diese neue konstruktive Lösung an den Schmierstoff, können dieselben Schmierstoffe Verwendung finden die sich bei Wälzlagern und Verzahnung bewährt haben, kann das Schmiersystem bleiben und kann auch die gleiche Strategie zu Ölwechselintervallen und Sauberkeit genutzt werden? Schlüsselwörter Windkraftgetriebe,Wälzlagerschäden, Gleitlager für Wellen, Gleitlager für Planeten, Schmierstoff Spezifikation, Schmierstoff Strategie Current wind turbine gearbox designs - in the power range from 2 up to 8 MW - typically consist of a combination of at least one planetary stage with at least one high speed helical gear stage. The majority of state-of-the-art designs are equipped with roller bearings. In the search for reliable solutions that are less prone to the specific failure mechanisms white etching crack WEC, the question arises whether plain bearings could be an alternative to the roller bearings. This paper presents the results from a gearbox development project of a 2 MW wind turbine gearbox with one planetary stage and 2 helical stages, in which roller bearings were substituted by plain bearings for all positions and that was tested on a test bench with respect to the most harmful operating conditions for plain bearings as starts and stops and idling. To ensure a reliable solution, insight is needed in relevant potential failure modes for plain bearings with respect to the lubrication on all positions. These potential failure modes need to be avoided by proper design rules that are relevant for the entire lifetime of a wind turbine gearbox (20 years) and validated with test procedures or measurements that are relevant to each risk. The result of the extensive testing was very promising so that the next step can be done to test on tower. Keywords Wind turbine Gearboxes, Rolling bearing failures, White Etching Cracks, Plain bearings for shafts, Plain bearings for planets, Lubricant specification, Lubrication strategy Kurzfassung Abstract T+S_4_17 07.06.17 17: 27 Seite 21 22 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 2 Design challenges with respect to lubrication • ZF Wind Power Antwerp started in 2011 to build up experience with plain bearings in a very early stage. • Some questions with respect to the lubrication of a plain bearing solution are • Can the same oil brands as for roller bearings be used for plain bearings? • Can the same lubrication system and equipment as pump and cooler be used for plain bearings? • Can the same lubrication strategy be used? 3 Roller bearing solution changed into plain bearing solution Beside the planet carrier bearings all roller bearings in the gear unit have been replaced by plain bearing with the goal to fit a plain bearing solution into the existing roller bearing dimensions. 4 Load conditions For dimensioning the plain bearings load conditions were defined with respect to generic turbine conditions. • 12 load cases were defined with respect to fictive turbine operating conditions • Main load case is load case 3 and maximum load case is 9. This load case 9 is used in the further investigations as max. load case. The detailed load conditions can be taken from table 1 and diagram 1. Aus Wissenschaft und Forschung ZF Wind Power Technology 4 12.-14.1.2016 Plain bearing lubrication in wind turbine gear boxes by Dirk-Olaf Leimann Roller bearing solution changed to plain bearing solution Change to plain bearings on all positions except planet carrier bearing Planet shaft (PL) Low speed shaft (LSS) High speed intermediate shaft (ISS) High speed shaft (HSS) Picture 1: Design of plain bearing solution The biggest challenge was the planet bearing and there were several possible solutions available. Plain Bearing Lubrication in Wind Turbine Gearboxes Dipl.- Ing. Dirk-Olaf Leimann ZF Wind Power, Lommel, Belgium Summary Current wind turbine gearbox designs in the power range from 2 up to 6 MW typically consist of a combination of at least one planetary stage with at least one high speed helical gear stage. The majority of state-of-the-art designs are equipped with roller bearings. In the search for reliable solutions that are less prone to the specific failure mechanisms white etching crack WEC, the question arises whether plain bearings could be an alternative to the roller bearings. This paper presents the results from a gearbox development project of a 2 MW wind turbine gearbox with one planetary stage and 2 helical stages, in which roller bearings were substituted by plain bearings for all positions and that was tested on a test bench with respect to the most harmful operating conditions for plain bearings as starts and stops and idling. To ensure a reliable solution, insight is needed in relevant potential failure modes for plain bearings with respect to the lubrication on all positions. These potential failure modes need to be avoided by proper design rules that are relevant for the entire lifetime of a wind turbine gearbox (20 years) and validated with test procedures or measurements that are relevant to each risk. The result of the extensive testing was very promising so that the next step can be done to test on tower. 1 Motivation to design and build a wind turbine gear unit with plain bearings • The reliability of roller bearing solutions is under discussion • „White Etching Crack (WEC) “ is a failure mode occurring in roller bearings used in wind turbine gear boxes, for already more than 20 years. Damage is typically seen in early stages of operation and can occur on different bearing positions. Damages are seen on almost all bearing designs. • Until today the root cause is not established. A number of theories have been developed but none of these theories is proven yet. • Plain bearing solutions are known as reliable solutions in many industrial applications. • There is a strong demand in the wind market to test plain bearings with the aim to increase wind turbine gearbox reliability. 2 Design challenges with respect to lubrication • ZF Wind Power Antwerp started in 2011 to build up experience with plain bearings in a very early stage. • Some questions with respect to the lubrication of a plain bearing solution are • Can the same oil brands as for roller bearings be used for plain bearings? • Can the same lubrication system and equipment as pump and cooler be used for plain bearings? • Can the same lubrication strategy be used? 3 Roller bearing solution changed into plain bearing solution Beside the planet carrier bearings all roller bearings in the gear unit have been replaced by plain bearing with the goal to fit a plain bearing solution into the existing roller bearing dimensions. Picture 1: Design of plain bearing solution The biggest challenge was the planet bearing and there were several possible solutions available. Picture 2: design solutions for planet bearings Out of the solutions the floating bush was selected as the best candidate to fulfil all requirements. The next picture shows the final design solutions for all positions. Picture 3: Shaft and planet solutions Plain Bearing Lubrication in Wind Turbine Gearboxes Dipl.- Ing. Dirk-Olaf Leimann ZF Wind Power, Lommel, Belgium Summary Current wind turbine gearbox designs in the power range from 2 up to 6 MW typically consist of a combination of at least one planetary stage with at least one high speed helical gear stage. The majority of state-of-the-art designs are equipped with roller bearings. In the search for reliable solutions that are less prone to the specific failure mechanisms white etching crack WEC, the question arises whether plain bearings could be an alternative to the roller bearings. This paper presents the results from a gearbox development project of a 2 MW wind turbine gearbox with one planetary stage and 2 helical stages, in which roller bearings were substituted by plain bearings for all positions and that was tested on a test bench with respect to the most harmful operating conditions for plain bearings as starts and stops and idling. To ensure a reliable solution, insight is needed in relevant potential failure modes for plain bearings with respect to the lubrication on all positions. These potential failure modes need to be avoided by proper design rules that are relevant for the entire lifetime of a wind turbine gearbox (20 years) and validated with test procedures or measurements that are relevant to each risk. The result of the extensive testing was very promising so that the next step can be done to test on tower. 1 Motivation to design and build a wind turbine gear unit with plain bearings • The reliability of roller bearing solutions is under discussion • „White Etching Crack (WEC) “ is a failure mode occurring in roller bearings used in wind turbine gear boxes, for already more than 20 years. Damage is typically seen in early stages of operation and can occur on different bearing positions. Damages are seen on almost all bearing designs. • Until today the root cause is not established. A number of theories have been developed but none of these theories is proven yet. • Plain bearing solutions are known as reliable solutions in many industrial applications. • There is a strong demand in the wind market to test plain bearings with the aim to increase wind turbine gearbox reliability. 2 Design challenges with respect to lubrication • ZF Wind Power Antwerp started in 2011 to build up experience with plain bearings in a very early stage. • Some questions with respect to the lubrication of a plain bearing solution are • Can the same oil brands as for roller bearings be used for plain bearings? • Can the same lubrication system and equipment as pump and cooler be used for plain bearings? • Can the same lubrication strategy be used? 3 Roller bearing solution changed into plain bearing solution Beside the planet carrier bearings all roller bearings in the gear unit have been replaced by plain bearing with the goal to fit a plain bearing solution into the existing roller bearing dimensions. Picture 1: Design of plain bearing solution The biggest challenge was the planet bearing and there were several possible solutions available. Picture 2: design solutions for planet bearings Out of the solutions the floating bush was selected as the best candidate to fulfil all requirements. The next picture shows the final design solutions for all positions. Picture 3: Shaft and planet solutions Plain Bearing Lubrication in Wind Turbine Gearboxes Dipl.- Ing. Dirk-Olaf Leimann ZF Wind Power, Lommel, Belgium Summary Current wind turbine gearbox designs in the power range from 2 up to 6 MW typically consist of a combination of at least one planetary stage with at least one high speed helical gear stage. The majority of state-of-the-art designs are equipped with roller bearings. In the search for reliable solutions that are less prone to the specific failure mechanisms white etching crack WEC, the question arises whether plain bearings could be an alternative to the roller bearings. This paper presents the results from a gearbox development project of a 2 MW wind turbine gearbox with one planetary stage and 2 helical stages, in which roller bearings were substituted by plain bearings for all positions and that was tested on a test bench with respect to the most harmful operating conditions for plain bearings as starts and stops and idling. To ensure a reliable solution, insight is needed in relevant potential failure modes for plain bearings with respect to the lubrication on all positions. These potential failure modes need to be avoided by proper design rules that are relevant for the entire lifetime of a wind turbine gearbox (20 years) and validated with test procedures or measurements that are relevant to each risk. The result of the extensive testing was very promising so that the next step can be done to test on tower. 1 Motivation to design and build a wind turbine gear unit with plain bearings • The reliability of roller bearing solutions is under discussion • „White Etching Crack (WEC) “ is a failure mode occurring in roller bearings used in wind turbine gear boxes, for already more than 20 years. Damage is typically seen in early stages of operation and can occur on different bearing positions. Damages are seen on almost all bearing designs. • Until today the root cause is not established. A number of theories have been developed but none of these theories is proven yet. • Plain bearing solutions are known as reliable solutions in many industrial applications. • There is a strong demand in the wind market to test plain bearings with the aim to increase wind turbine gearbox reliability. 2 Design challenges with respect to lubrication • ZF Wind Power Antwerp started in 2011 to build up experience with plain bearings in a very early stage. • Some questions with respect to the lubrication of a plain bearing solution are • Can the same oil brands as for roller bearings be used for plain bearings? • Can the same lubrication system and equipment as pump and cooler be used for plain bearings? • Can the same lubrication strategy be used? 3 Roller bearing solution changed into plain bearing solution Beside the planet carrier bearings all roller bearings in the gear unit have been replaced by plain bearing with the goal to fit a plain bearing solution into the existing roller bearing dimensions. Picture 1: Design of plain bearing solution The biggest challenge was the planet bearing and there were several possible solutions available. Picture 2: design solutions for planet bearings Out of the solutions the floating bush was selected as the best candidate to fulfil all requirements. The next picture shows the final design solutions for all positions. Picture 3: Shaft and planet solutions Picture 3: Shaft and planet solutions ZF Wind Power Technology 5 12.-14.1.2016 Plain bearing lubrication in wind turbine gear boxes by Dirk-Olaf Leimann Comparison of possible plain bearing solutions for the planets ZF Wind Power’s actual solution to be replaced: Integrated taper roller bearings Fixed bushing (s) Floating bush Coated planet gear Candidate plain bearing and lubrication solutions Picture 2: design solutions for planet bearings 4 Load conditions For dimensioning the plain bearings load conditions were defined with respect to generic turbine conditions. 12 load cases were defined with respect to fictive turbine operating conditions Main load case is load case 3 and maximum load case is 9. This load case 9 is used in the further investigations as max. load case. The detailed load conditions can be taken from table 1 and diagram 1. Table 1: load cases Diagram 1: load cases and distribution 5 Detailed analysis of the lubrication conditions In the following tables the results are shown from the detailed analysis of all plain bearings with respect to contact pressure and lubrication film thickness for load case 9 which is the maximum load case with duration of 3 % of the total life. 5.1 Planet bearing Table 2 gives an overview on average values from the whole bearing at load case 9. . ! " # " ! " $% ! & ' ' ' ( & ) * ' ' ' # " ! + ' ' ! + ' ' , - ' ' ' $ ./ ' ' ' 0 12 ' ' Table 2: basic values planet bearing @ load case 9 For the planet bearing also the frictional moment was calculated because there was the fear of wear due to very slow motion. Diagram 2: frictional moment planet bearing @ load case 9 A comparison was done on contact pressure versus permissible material values for load case 9. 0 3 + 3 $ ' , , , , Table 3: contact pressure @ load case 9 and permissible material values Diagram 3: load case 9 comparison strength / pressure 5.2 Shaft bearings LSS Tables 4 / 5 give an overview on values from the bearings at generator side GS and rotor side RS at load case 9. ! " # %** 3* ! & ' ( & ) * ' # " ! + ' ! + ' , - ' $ ./ ' 0 12 ' Table 4: basic values LSS RS bearing @ load case 9 Diagram 1: load cases and distribution Out of the solutions the floating bush was selected as the best candidate to fulfil all requirements. The next picture shows the final design solutions for all positions. Table 1: load cases Table 1: load cases Diagram 1: load cases and distribution 5 Detailed analysis of the lubrication conditions In the following tables the results are shown from the detailed analysis of all plain bearings with respect to contact pressure and lubrication film thickness for load case 9 which is the maximum load case with duration of 3 % of the total life. 5.1 Planet bearing Table 2 gives an overview on average values from the whole bearing at load case 9. . ! " # " ! " $% ! & ' ' ' ( & ) * ' ' ' # " ! + ' ' ! + ' ' , - ' ' ' $ ./ ' ' ' 0 12 ' ' Table 2: basic values planet bearing @ load case 9 For the planet bearing also the frictional moment was calculated because there was the fear of wear due to very slow motion. Diagram 2: frictional moment planet bearing @ load case 9 A comparison was done on contact pressure versus permissible material values for load case 9. 0 3 + 3 $ ' , , , , Table 3: contact pressure @ load case 9 and permissible material values Diagram 3: load case 9 comparison strength / pressure 5.2 Shaft bearings LSS Tables 4 / 5 give an overview on values from the bearings at generator side GS and rotor side RS at load case 9. ! " # %** 3* ! & ' ( & ) * ' # " ! + ' ! + ' , - ' $ ./ ' 0 12 ' Table 4: basic values LSS RS bearing @ load case 9 T+S_4_17 07.06.17 17: 27 Seite 22 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 5 Detailed analysis of the lubrication conditions In the following tables the results are shown from the detailed analysis of all plain bearings with respect to contact pressure and lubrication film thickness for load case 9 which is the maximum load case with duration of 3 % of the total life. 5.1 Planet bearing Table 2 gives an overview on average values from the whole bearing at load case 9. 5.2 Shaft bearings LSS Tables 4 / 5 give an overview on values from the bearings at generator side GS and rotor side RS at load case 9. 23 Aus Wissenschaft und Forschung Diagram 2: frictional moment planet bearing at load case 9 Diagram 3: load case 9 comparison strength / pressure Table 2: basic values planet bearing at load case 9 Table 4: basic values LSS RS bearing @ load case 9 Table 5: basic values LSS GS bearing @ load case 9 Table 6: basic values LSS RS bearing @ load case 9 Table 3: contact pressure at load case 9 and permissible material values 4 Load conditions For dimensioning the plain bearings load conditions were defined with respect to generic turbine conditions. 12 load cases were defined with respect to fictive turbine operating conditions Main load case is load case 3 and maximum load case is 9. This load case 9 is used in the further investigations as max. load case. The detailed load conditions can be taken from table 1 and diagram 1. Table 1: load cases Diagram 1: load cases and distribution 5 Detailed analysis of the lubrication conditions In the following tables the results are shown from the detailed analysis of all plain bearings with respect to contact pressure and lubrication film thickness for load case 9 which is the maximum load case with duration of 3 % of the total life. 5.1 Planet bearing Table 2 gives an overview on average values from the whole bearing at load case 9. . ! " # " ! " $% ! & ' ' ' ( & ) * ' ' ' # " ! + ' ' ! + ' ' , - ' ' ' $ ./ ' ' ' 0 12 ' ' Table 2: basic values planet bearing @ load case 9 For the planet bearing also the frictional moment was calculated because there was the fear of wear due to very slow motion. Diagram 2: frictional moment planet bearing @ load case 9 A comparison was done on contact pressure versus permissible material values for load case 9. 0 3 + 3 $ ' , , , , Table 3: contact pressure @ load case 9 and permissible material values Diagram 3: load case 9 comparison strength / pressure 5.2 Shaft bearings LSS Tables 4 / 5 give an overview on values from the bearings at generator side GS and rotor side RS at load case 9. ! " # %** 3* ! & ' ( & ) * ' # " ! + ' ! + ' , - ' $ ./ ' 0 12 ' Table 4: basic values LSS RS bearing @ load case 9 For the planet bearing also the frictional moment was calculated because there was the fear of wear due to very slow motion. A comparison was done on contact pressure versus permissible material values for load case 9. 5.3 Shaft bearings ISS Tables 6 / 7 contain values from the bearings at generator side GS and rotor side RS at load case 9. ZF Wind Power Technology 3 12.-14.1.2016 Plain bearing lubrication in wind turbine gear boxes by Dirk-Olaf Leimann Diagramm 2 mm ra g a i D 2 mm 3 6 1 0 2 . 1 . 4 -1 . 2 1 d n i w n i n o i t ca ri b u l g n ri a e b n i a Pl e L f a l rk-O i D y b s xe o b r a e g e n i rb u t n n ma i e W F Z y g o l o n ch r e w Po d n i ZF Wind Power Technology 4 12.-14.1.2016 Plain bearing lubrication in wind turbine gear boxes by Dirk-Olaf Leimann Diagramm 3 mm ra g a i D 3 mm 4 6 1 0 2 . 1 . 4 -1 . 2 1 d n i w n i n o i t ca ri b u l g n ri a e b n i a Pl e L f a l rk-O i D y b s xe o b r a e g e n i rb u t n n ma i e W F Z y g o l o n ch r e w Po d n i T+S_4_17 07.06.17 17: 27 Seite 23 24 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 5.4 Shaft bearings HSS Tables 8 / 9 contain values from the bearings at generator side GS and rotor side RS at load case 9. 6 Oil selection criteria For roller bearings oil selection criteria have been specified by all bearings manufacturers and are also applied by ZF Wind Power in the oil approval procedure. However, specific criteria for plain bearings are not available yet. 6.1 ZF WP criteria for roller bearings Aus Wissenschaft und Forschung Table 7: basic values LSS GS bearing @ load case 9 Table 8: basic values LSS RS bearing @ load case 9 Table 9: basic values LSS GS bearing @ load case 9 Table 10: oil selection criteria adapted from FAG Table 11: oil selection criteria adapted from SKF Table 12: ZF WP preliminary criteria for plain bearings criteria adapted from SKF 5.5 Results of the detailed analysis • Contact surface stresses are much lower than gearing and original roller bearings • Temperatures are similar to gears and the original roller bearings • Friction losses are in sum equal to the values of the roller bearings • Friction losses of the plain bearings in the planets are much lower than the roller bearings • Friction losses of the plain bearings on intermediate shafts are equal the roller bearings • Friction losses of the plain bearings on high speed shaft are higher than the roller bearings 6.2 ZF WP preliminary criteria for plain bearings T+S_4_17 07.06.17 17: 27 Seite 24 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 The table 12 gives a first approach to the question how the plain bearing material react with oil and deals with stricter requirements with respect to copper corrosion, foaming and wear resistance. 7 Materials used for the plain bearings 9 Design of the lubrication system • The oil lubrication system of this prototype consists of • a mechanical pump • an electrical pump • Both pumps are working on a separate circuit • Two filter and cooler units are used • The separate circuits are used for the gears and the bearings and can be switched according to the operation conditions and situation. 25 Aus Wissenschaft und Forschung Table 13: materials used for the planet and shaft bearings 8 Design of a specific oil test for plain bearing material A leach, surface and hardness test was created and carried out with the material used in the plain bearings of the prototype. The above mentioned ZF WP method (table 12) is documented in the pictures below and had a duration of 21 days at 100 °C. Picture 4: MW 89 Picture 5: MB 551 The result is shown in table 15. Table 14: lab results for the leach test, (glijlagen = Gleitschicht = white metal layer = material MW89) Picture 6: gear unit and lubrication syste Picture 7: Filter and cooling syste Picture 8: roller bearing solution Picture 9: plain bearing solution 9.1 Lubrication of the shaft bearings The internal piping for the plain bearings solution differs only slightly from the roller bearing solution. T+S_4_17 07.06.17 17: 27 Seite 25 26 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 9.2 Lubrication of the planet bearings The oil supply system for the plain bearings of the planets was kept the same as for the taper roller bearings. • Noise and vibration measurements • Visual inspection after disassembly Aus Wissenschaft und Forschung Picture 10: roller bearing solution Picture 11: plain solution bearing 10 Lubrication strategies Strategies are necessary for the operation of the gear unit, i.e. : • Lubrication strategies are derived from operating conditions • Start up o Electrical pump for plain bearings, mechanical pump for gears • Running o Both pumps working on one circuit • Stop o Electrical pump for plain bearings, mechanical for gears • Grid loss o Mechanical pump for plain bearings 11 Test and measurement program on the 4,5 MW test rig Test program: • Load test 1 (functional test): Test (18h) run in, no load, load steps from -33% to +110% nominal load, measurements, limited load test (35h) with start-stop cycles and load cycles • Duration test 2: (440h + 1312h): many startstops and load cycles, long test cycles with idling Measurements: • Bearing temperatures and oil flow (except on planet bearings) • Online cleanliness measurements for oil condition • Oil samples with lab measurements • Check on all gear contact patterns and gear teeth in regular time intervals • Noise and vibration measurements • Visual inspection after disassembly Picture 12: test load cycles 11.1 Load test 1 (18h) & 2 (35h) • Run in • Idling test (variable speed) • Load and speed variations • Overload • Measurement and comparison of • Temperatures at HSS, .. • Particle count in the oil (14/ 11/ 9) • Oil analysys • Contact pattern gears • Vibrations • Noise level 11.2 Duration test 2 $ $ : $ ! #,# * " ' * ' Table 15: list of tests and duration 11.3 Particle count Diagram 4: Particle count versus time 12 Test results After concluding all tests the gear box was disassembled and all parts were visually inspected. The plain bearings have been measured and compared with respect to the original dimensions. Special attention was given to wear values because of the large number of starts/ stops and idling. 12.1 Planet bearing / floating bush The results are listed in table 17: no significant wear was found and the bearing is still in best condition. ? # ! ! ) & @ $% $% $% 5 A C B A C B A C C C C 2 ) C 2 ) C 2 ) C " C " C " C " C " C " C " C " C Table 16: Wear due to operation conditions measured at planet floating bush Picture 12: test load cycles 10 Lubrication strategies Strategies are necessary for the operation of the gear unit, i. e.: • Lubrication strategies are derived from operating conditions • Start up • Electrical pump for plain bearings, mechanical pump for gears • Running • Both pumps working on one circuit • Stop • Electrical pump for plain bearings, mechanical for gears • Grid loss •Mechanical pump for plain bearings 11 Test and measurement program on the 4,5 MW test rig Test program: • Load test 1 (functional test): Test (18h) run in, no load, load steps from -33% to +110% nominal load, measurements, limited load test (35h) with start-stop cycles and load cycles • Duration test 2: (440h + 1312h): many startstops and load cycles, long test cycles with idling Measurements: • Bearing temperatures and oil flow (except on planet bearings) • Online cleanliness measurements for oil condition • Oil samples with lab measurements • Check on all gear contact patterns and gear teeth in regular time intervals 11.1 Load test 1 (18h) & 2 (35h) • Run in • Idling test (variable speed) • Load and speed variations • Overload • Measurement and comparison of • Temperatures at HSS, .. • Particle count in the oil (14/ 11/ 9) • Oil analysys • Contact pattern gears • Vibrations • Noise level 11.2 Duration test 2 Table 15: list of tests and duration Diagram 4: Particle count versus time 11.3 Particle count T+S_4_17 07.06.17 17: 27 Seite 26 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 12 Test results After concluding all tests the gear box was disassembled and all parts were visually inspected. The plain bearings have been measured and compared with respect to the original dimensions. Special attention was given to wear values because of the large number of starts/ stops and idling. 12.1 Planet bearing / floating bush The results are listed in table 17: no significant wear was found and the bearing is still in best condition. Because of the involute design of the gears more than 100 µm wear would be allowable, so that a lifetime of 20 years is possible; however, it has to be proven by field testing. 27 Aus Wissenschaft und Forschung Table 16: Wear due to operation conditions measured at planet floating bush Table 18: wear on shaft bearings Table 17: run in values surface roughness 12.2 Running in due to operating conditions measured at shaft bearings Running-in could be observed on all shaft bearings which (white metal coated). 12.3 Wear due to operating conditions measured at the shaft bearings Wear was observed on almost all shaft bearings but to a very small extent. As the white metal layer has a thickness of about 1 mm, this observation is seen as not design-critical. As a whole it can be stated that all bearings can still be used. 12.4 Disassembly results, visual report 12.4.1 Planet bearing Picture 13: planet with planet bearings Picture 14 and 15: inner and outer raceway of the planet bearing T+S_4_17 07.06.17 17: 27 Seite 27 28 Tribologie + Schmierungstechnik 64. Jahrgang 4/ 2017 Contact surfaces: • Inner raceway floating bush • No wear visible, small scratches from particles • Outer raceway floating bush • No wear visible, small scratches from particles • Some longitudinal scratches due to disassembly Raceways have scratches; the amount of wear is shown in table 18. 13 Reliability The results from the bench tests are promising. Even in worst case operating conditions, such as starts/ stops and idling conditions no wear can be observed in the planet bearings and only a small amount of wear was found in the shaft bearings. However, statements on reliability will have to come from field tests and field experience. 14 Summary • Lubrication of plain bearings can be handled with the approach that is in use with roller bearings in wind turbine applications. • ZF WP reference oil Mobilgear SHC XMP 320 behaves well. • The lubrication system and cooling system can be kept. • Lubrication strategy is adapted to the use of plain bearings Aus Wissenschaft und Forschung Picture 16 and 17: axial raceway of the planet bearing Picture 18, 19 and 20: radial raceway of shaft bearings ISS GS, ISS RS, HSS RS 12.4.2 Shaft bearings Anzeige Hier könnte auch IHRE Firmen-Information zu finden sein! Wenn auch Sie die Leser von T + S über Ihre aktuellen Broschüren und Kataloge informieren möchten, empfehlen wir Ihnen, diese Werbemöglichkeit zu nutzen. Für weitere Informationen - wie Gestaltung, Platzierung, Kosten - wenden Sie sich bitte an Frau Sigrid Hackenberg, die Ihnen jederzeit gerne mit Rat und Tat zur Verfügung steht. 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