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— A Drivetrain Solution for Large-Scale Wind Turbines
As wind turbine rated capacities continue to rise, the loads carried by the drivetrain increase accordingly. The drivetrain must transmit the enormous torque generated by the rotor within the confined space of the nacelle, and its reliability directly affects the power generation efficiency and service life of the entire turbine. The main bearing is the most mechanically complex component in the drivetrain, simultaneously subjected to radial forces, axial forces, and overturning moments. Its performance is one of the key factors limiting the development of large wind turbines.
I. Challenges Posed by Wind Turbine Upscaling to the Drivetrain
1.1 Large Turbines Become the Industry Mainstream
The rated capacity of globally installed wind turbines is increasing rapidly. Onshore turbines have advanced from the 3 MW class to the 6–8 MW class, while offshore turbines have entered the stage of large-scale deployment above 10 MW, with 15 MW and 20 MW prototypes successively rolling off the production line. Take the Siemens Gamesa SG DD-276 as an example: it has a rated capacity of 21.5 MW, a rotor diameter of 276 meters, and a blade sweep area exceeding 60,000 square meters. A single unit can generate enough electricity to power approximately 20,000 households per year.
The core driver of turbine upscaling is the reduction of the Levelized Cost of Energy (LCOE). Larger rotors improve wind energy capture efficiency, while higher rated capacities dilute the unit costs of foundations, lifting, and operation and maintenance (O&M). However, upscaling is not simply a matter of enlarging dimensions — every component faces multiple constraints in terms of load, space, reliability, and cost.
1.2 The Drivetrain Is the Core of Power Transmission
The drivetrain converts the wind energy captured by the rotor into mechanical energy, which is then stepped up by the gearbox to drive the generator. A typical doubly-fed or semi-direct-drive drivetrain consists of the hub, mainshaft, main bearing, gearbox, coupling, and generator connected in series.
In large turbines, the drivetrain operates under more demanding conditions: the increase in rotor diameter causes the blade weight and aerodynamic loads to grow nonlinearly, and the radial forces, axial forces, and overturning moments acting on the drivetrain can reach thousands of kilonewtons. The internal space of the nacelle is limited, so the drivetrain must be compactly arranged. The failure of any component can lead to a complete turbine shutdown, and the cost of a single O&M operation for an offshore turbine can reach hundreds of thousands or even millions of yuan.
1.3 The Main Bearing Is the Load-Bearing Core of the Drivetrain
The main bearing supports the entire rotor–mainshaft system and simultaneously withstands loads in three directions: radial loads (the self-weight of the rotor and mainshaft), axial loads (wind thrust), and overturning moments (yaw-induced and turbulence-induced tilting moments). The design life of a main bearing is typically required to exceed 20 years (approximately 175,000 hours).
Therefore, the selection and design of the main bearing directly determine the reliability of the drivetrain and the entire turbine. As turbine capacities increase, the limitations of traditional main bearing solutions have gradually emerged, and the industry needs a new solution with higher load-carrying capacity, greater reliability, and a balanced approach to cost and space efficiency.
II. Limitations of Traditional Solutions: Inherent Problems of TRB/DTRB Main Bearings
2.1 Current Mainstream Technical Routes
At present, the main bearings of turbines above 8 MW still predominantly use Tapered Roller Bearings (TRB), mainly in two configurations: two single-row tapered roller bearings arranged back-to-back or face-to-face (TRB+TRB), or one double-row tapered roller bearing (Double-row Tapered Roller Bearing, DTRB). Both solutions have been long-term validated on medium and small capacity turbines, but their inherent deficiencies have become increasingly apparent in large turbines.
2.2 TRB+TRB Configuration: The Traditional Layout of Dual Bearings Plus a Long Mainshaft
TRB+TRB is currently the most widely used traditional layout. The rotor hub is bolted to the front end of the mainshaft, two main bearings are arranged at axial intervals on the mainshaft, and the rear end of the mainshaft is bolted to the gearbox input shaft. The two bearings jointly carry the radial, axial, and overturning moments, forming a simply supported beam-type support system.
This solution is technically mature and distributes the load relatively evenly across each bearing, but its drawbacks are also significant. First, to ensure the concentricity and preload consistency of the two bearings, the mainshaft must have sufficient length and stiffness, resulting in a heavy drivetrain with a long axial dimension. Second, the installation of the two bearings imposes high requirements on concentricity, perpendicularity, and preload, making the on-site assembly process complex; any deviation can easily cause uneven loading and premature failure. Third, the mainshaft is a large forging, and its material cost, machining cycle, and transportation difficulty increase significantly with turbine capacity.
2.3 DTRB Configuration: A Compromise of Double-Row Integration
The DTRB integrates two rows of tapered rollers into a single bearing, shortening the axial dimension and reducing the machining and assembly workload of one bearing housing. However, it is still essentially a combination of tapered roller bearings and does not fundamentally solve the inherent problems: the contact between the raceway and the rollers is line contact with high contact stress; precise preload is required to ensure stiffness, and when preload is insufficient, stiffness can decrease by 15%–20% with rotational speed; under heavy load conditions, the sliding friction between the large end faces of the rollers and the ribs causes severe heat generation and poor lubrication conditions.
2.4 Quality Issues Exposed During Operation
As operating time accumulates, failures of TRB and DTRB solutions occur frequently and have become one of the main pain points affecting the reliability of large turbines. Typical failure modes include:
Raceway pitting: Under the action of alternating contact stress, fatigue pitting appears on the raceway surface, which in severe cases propagates into spalling, causing a sharp increase in vibration and noise.
Rolling element spalling: Material fatigue and detachment from the roller surface generate abrasive particles that enter the lubrication system and accelerate the wear of other components.
Mainshaft axial displacement: Preload decay or increased bearing clearance causes axial displacement of the mainshaft, affecting gearbox meshing accuracy and triggering cascading failures.
Cage fracture: Under impact loads and high-speed rotation, the cage is subjected to complex forces, and cage fracture cases are particularly prominent in DTRB solutions.
These failures not only cause unplanned shutdowns but may also lead to secondary damage to downstream components such as the gearbox and generator, keeping the total life-cycle maintenance cost high. Industry data show that main bearing-related failures account for more than 30% of wind turbine drivetrain failures, making them one of the major O&M challenges for offshore wind turbines.
III. The JUNHUAN Solution: Three-Row Cylindrical Roller Main Bearing Compact Drivetrain
3.1 JUNHUAN’s Technical Accumulation
JUNHUAN has long focused on the design of drivetrain solutions using three-row cylindrical roller slewing bearings (Three-row Cylindrical Roller Bearing, 3CRB) as main bearings. Unlike traditional bearing suppliers that only provide a single bearing product, JUNHUAN starts from the overall drivetrain architecture and provides an integrated solution covering main bearing selection, structural design, installation process, lubrication and sealing, and full life-cycle maintenance.
When used as a main bearing, the JUNHUAN three-row cylindrical roller slewing bearing can operate for more than 20 years under the same working conditions without experiencing quality problems similar to those of TRB/DTRB bearings. Long-term operating data demonstrate that the three-row cylindrical roller slewing bearing is better suited to the main bearing requirements of large megawatt-class wind turbines.
3.2 Core Innovation: Architectural Breakthrough Through Mainshaft Elimination
The core of the JUNHUAN compact drivetrain is the replacement of the traditional “dual bearings plus mainshaft” combination with a three-row cylindrical roller main bearing, achieving simplification from the root of the drivetrain structure rather than simply upgrading a single component.
In traditional solutions, the mainshaft is a necessary intermediate component connecting the hub and the gearbox, and two main bearings are mounted on the mainshaft to form the support system. The JUNHUAN solution leverages the high load-carrying capacity of the three-row cylindrical roller main bearing to integrate the support function directly between the hub and the gearbox, eliminating the traditional long mainshaft structure.
3.3 Structure of the Compact Drivetrain
The typical structure of the JUNHUAN three-row cylindrical roller main bearing compact drivetrain is as follows: the rotor hub is directly connected to the inner ring (or outer ring) of the three-row cylindrical roller main bearing, the other side of the main bearing is directly connected to the gearbox input end, the gearbox output end is connected to the generator through a coupling, the entire system is mounted on the nacelle bedplate, and the bedplate is connected to the tower below.
Compared with the traditional TRB+TRB solution, the structure has undergone fundamental changes:
Elimination of the long mainshaft: The three-row cylindrical roller main bearing is directly integrated between the hub and the gearbox, eliminating the need for a long mainshaft running through two bearings and significantly shortening the axial dimension of the drivetrain.
Integrated support: Radial load-carrying, axial load-carrying, and overturning moment resistance are integrated into a single bearing, with three rows of rollers with clearly defined functions, eliminating the need for a combination of two bearings.
Direct bolt fixing: The main bearing is directly connected to the hub and gearbox by bolts, without the need for precision shrink fitting and preload adjustment, greatly simplifying the installation process.
Compact layout: The entire drivetrain (hub – main bearing – gearbox – generator) is arranged compactly along the axial direction, saving nacelle space and enabling the nacelle layout of even larger capacity turbines.
3.4 Solution Value: Weight Reduction, Space Savings, and High Efficiency
The “mainshaft elimination” design solves the load problem through the high load-carrying capacity of the three-row cylindrical roller main bearing, while reducing the weight of the entire drivetrain by more than 50% and adapting to nacelle space constraints through a compact structure.
The weight reduction of more than 50% mainly comes from three aspects. First, the elimination of the large mainshaft forging directly reduces several thousand kilograms of metal weight. Second, the three-row cylindrical roller main bearing adopts an integral race structure, which is more compact and has higher material utilization compared with the combination of two independent bearings plus bearing housings. Third, after the axial dimension of the drivetrain is shortened, the material used for the nacelle bedplate and frame is correspondingly reduced. These weight reductions not only lower manufacturing costs but more importantly reduce the loads on the tower and foundation, with an amplifying effect on the overall turbine cost reduction.
What JUNHUAN provides is not a single bearing component but an overall drivetrain solution optimized at the architectural level.
IV. Six-Dimension Comparison: 3CRB vs TRB vs DTRB
In terms of core performance, the three-row cylindrical roller main bearing (3CRB) outperforms TRB and DTRB across all six dimensions: load-carrying capacity, structural stiffness, installation difficulty, transmission efficiency, reliability, and comprehensive cost.
In terms of load-carrying capacity, TRB is the weakest of the three and is prone to overload under heavy loads. DTRB offers a relatively weak radial load-carrying capacity despite its two-row integration. 3CRB, with three rows of rollers assigned clearly defined functions for radial loads, axial loads, and overturning moments, delivers the strongest load-carrying capacity.
In terms of structural stiffness, TRB relies on an external combination of two bearings for overturning resistance, and its stiffness is inherently limited. DTRB depends heavily on preload — when preload is insufficient, its stiffness decreases by 15%–20% with rotational speed. 3CRB combines line contact with an integral race structure, achieving a stiffness nearly 50% higher than TRB.
In terms of installation difficulty, TRB imposes extremely high requirements on concentricity, perpendicularity, and preload, making assembly complex. DTRB still requires precise positioning and preload, and the difficulty remains relatively high. 3CRB uses direct bolt fixing without precision assembly, making installation simple and fast.
In terms of transmission efficiency, TRB typically achieves 92%–95%, but poor concentricity causes significant friction loss. DTRB also operates at 92%–95%, with additional friction generated by mainshaft preload. 3CRB reaches 94%–97%, the highest among the three, thanks to its shaftless design and even load distribution.
In terms of typical failures, TRB suffers from frequent raceway pitting, rolling element spalling, and mainshaft axial displacement. DTRB is prone to raceway pitting and cage fracture, with a relatively short service life. 3CRB exhibits high reliability, with only occasional minor cage issues caused by improper maintenance and no record of batch failures.
In terms of comprehensive cost, TRB has a high manufacturing cost, frequent maintenance, and a high life-cycle cost. DTRB has a moderate manufacturing cost but a high maintenance cost, also resulting in a high life-cycle cost. 3CRB has a higher unit cost, but its maintenance cost is reduced by 60% and its life-cycle cost is reduced by 20%.
4.1 Load-Carrying Capacity: Three-Row Division of Labor vs Single-Row Overload
TRB is a single-row tapered roller bearing with line contact between the rollers and the raceway. Theoretically, it can simultaneously carry radial and axial loads. However, under the ultra-thousand-ton loads of large megawatt-class wind turbines, the contact area of a single row of rollers is limited, and the contact stress can easily exceed the allowable value of the material, leading to overload under heavy loads. DTRB integrates two rows of rollers, improving the radial load-carrying capacity to some extent, but it is still limited by the geometric characteristics of tapered rollers, and its radial load-carrying capacity remains relatively weak.
3CRB adopts a three-row cylindrical roller structure, with the three rows of rollers divided by function: one row carries radial loads, and the other two rows respectively carry bidirectional axial loads and overturning moments. Each row of rollers operates in its optimal load direction, the load distribution is uniform, the contact stress is significantly reduced, and the overall load-carrying capacity far exceeds that of TRB and DTRB.
4.2 Structural Stiffness: Integral Race vs Preload Dependence
The overturning resistance of the TRB solution depends on the external combination of two bearings (span arrangement), and its stiffness is limited by the bearing span and mainshaft stiffness. Although DTRB integrates two rows, its stiffness is highly dependent on preload — when preload is insufficient, bearing stiffness can decrease by 15%–20% with rotational speed, which is particularly disadvantageous under the variable-speed operating conditions of wind turbines; excessive preload leads to frictional heat generation and premature wear.
3CRB adopts a line contact plus integral race structure, and both the inner and outer rings of the bearing are integral forgings with higher rigidity than split structures. The three rows of rollers cooperate with the integral race to form a high-stiffness support system, with structural stiffness nearly 50% higher than the TRB solution. High stiffness means smaller deformation, which helps ensure gearbox meshing accuracy, reduces vibration and noise, and extends the service life of the drivetrain.
4.3 Installation Difficulty: Bolt Fixing vs Precision Assembly
The installation of the TRB+TRB solution is one of the most complex steps in drivetrain assembly. The two bearings require extremely high concentricity and perpendicularity, and preload adjustment requires professional equipment and extensive experience, making the assembly process complex and the on-site installation cycle long. Installation deviation of either bearing can lead to uneven loading, heat generation, or even premature failure. Although DTRB reduces the installation of one bearing, it still requires precise positioning and preload, and the difficulty remains relatively high.
3CRB adopts direct bolt fixing: the main bearing is directly connected to the hub and gearbox through face bolts, without shrink fitting, preload adjustment, or precision alignment, making installation simple and fast. This not only shortens the on-site installation cycle and reduces dependence on installer skills but more importantly eliminates the risk of premature failure caused by improper installation.
4.4 Transmission Efficiency: Even Load Distribution vs Friction Loss
The transmission efficiency of the TRB solution is typically between 92% and 95%. Since the two bearings are mounted separately on the mainshaft, concentricity errors are difficult to eliminate completely, resulting in additional sliding friction between the rollers and the raceway and significant friction loss. The efficiency of DTRB is also between 92% and 95%, and the mainshaft preload applied to ensure stiffness generates additional friction, further reducing transmission efficiency.
The transmission efficiency of 3CRB can reach 94%–97%, the highest among the three solutions. The efficiency advantage mainly comes from two aspects: first, the shaftless design eliminates the additional friction caused by mainshaft concentricity errors; second, the three rows of rollers have clearly defined functions and uniform load distribution, so each row operates in its optimal state with minimal friction loss. For large wind turbines, every 1 percentage point increase in transmission efficiency means tens of thousands of additional kilowatt-hours of electricity per year, with considerable economic benefits over a 20-year service life.
4.5 Typical Failures: The Essential Difference in Reliability
Typical failures of the TRB solution include frequent raceway pitting, rolling element spalling, and mainshaft axial displacement. The root causes of these failures are the high contact stress and complex stress state of tapered rollers, as well as the preload decay problem associated with the combination of two bearings. In addition to raceway pitting, the cage fracture problem is particularly prominent in the DTRB solution, and its overall service life is relatively short.
3CRB demonstrates high reliability in long-term operation, with only occasional minor cage problems due to improper maintenance and no record of batch failures. This reliability difference is determined by the structural essence: the contact stress of cylindrical rollers is lower than that of tapered rollers; the integral race structure avoids the deformation incoordination of split structures; the three-row division of labor ensures uniform load distribution; and the bolt-fixed installation eliminates installation deviations. The combination of multiple factors enables 3CRB to maintain stable performance over an operating cycle of more than 20 years.
4.6 Comprehensive Cost: A Life-Cycle Perspective
In terms of unit cost, 3CRB has a higher manufacturing cost per unit than TRB and DTRB due to its large integral forgings and three-row roller structure, which is also the main reason some owners hesitate during initial selection. However, from the perspective of Life Cycle Cost (LCC), the advantages of 3CRB are clear:
Maintenance cost reduced by 60%: 3CRB has high reliability and few failures, significantly reducing unplanned shutdowns and maintenance frequency. For offshore wind turbines, the cost of a single O&M operation, including vessel rental, lifting, and labor, can reach hundreds of thousands of yuan, and the reduction in maintenance frequency directly translates into cost savings.
Life-cycle cost reduced by 20%: Taking into account manufacturing cost, installation cost, maintenance cost, downtime losses, and improved power generation efficiency, the total cost of the 3CRB solution over a 20-year service life is approximately 20% lower than that of TRB/DTRB solutions.
Therefore, judging the merits of a main bearing solution should not be based solely on the initial purchase price but should be comprehensively evaluated from the perspective of life-cycle cost. Although the 3CRB solution requires a higher initial investment, its advantages in reliability, efficiency, and maintenance cost can deliver significant returns on investment over the turbine’s operating cycle.
V. Reliability Verification: Laboratory Testing and Wind Farm Operation
5.1 Materials and Heat Treatment Process
JUNHUAN continuously iterates in the fields of materials science and heat treatment processes to develop high-performance three-row cylindrical roller main bearings. The purity, carbide uniformity, and quenched and tempered microstructure of bearing steel directly determine the fatigue life and reliability of the bearing. JUNHUAN uses high-purity bearing steel and strictly controls the oxygen content and non-metallic inclusions in the steel through processes such as vacuum degassing and refining. In the heat treatment stage, the quenching temperature, cooling rate, and tempering process are precisely controlled to ensure a uniform high-hardness hardened layer and an ideal residual compressive stress distribution on the raceway surface, laying the foundation for the long service life and high reliability of the bearing at the material level.
5.2 Laboratory Testing
Before being launched to the market, JUNHUAN three-row cylindrical roller main bearings undergo rigorous laboratory testing covering multiple dimensions such as deformation, load limit, fatigue life, temperature rise, and lubrication performance:
Deformation testing: The radial and axial deformations of the inner and outer bearing rings are measured under rated and ultimate loads to verify whether the structural stiffness meets the design requirements.
Load limit testing: Loads are applied gradually until the bearing reaches its ultimate load-carrying state, verifying the safety and margin of the bearing under extreme working conditions.
Fatigue life testing: Long-duration running tests are conducted under an accelerated load spectrum to verify whether the fatigue life of the bearing meets the 20-year design life requirement.
Test results show that the deformation, load limit, and service life of JUNHUAN three-row cylindrical roller main bearings all meet the highest industry standards and can meet the long-term use requirements of turbines above 5 MW.
5.3 Field Project Verification
In addition to laboratory testing, JUNHUAN three-row cylindrical roller main bearings have also been extensively verified in field projects. Long-term operating data from multiple wind power projects in Europe show that the load-carrying capacity of three-row cylindrical roller main bearings is superior to that of TRB and DTRB main bearings, with stable and reliable operating performance.
The verification results of offshore wind power projects are particularly noteworthy. The offshore wind environment is characterized by strong impacts, high salt spray corrosion, and high turbulence intensity, imposing more stringent requirements on the reliability of main bearings. JUNHUAN three-row cylindrical roller main bearings have demonstrated excellent corrosion resistance and impact resistance in offshore projects, maintaining stable performance even under strong impact and high salt spray corrosion environments, with no record of batch failures. These field operating data corroborate the laboratory test results, verifying the reliability and adaptability of the JUNHUAN three-row cylindrical roller main bearing solution.
VI. Conclusion
Faced with the challenge of wind turbine upscaling, traditional TRB/DTRB main bearing solutions can no longer meet the requirements of large megawatt-class turbines in terms of load-carrying capacity, stiffness, reliability, and life-cycle cost. The JUNHUAN three-row cylindrical roller main bearing compact drivetrain solution, through the architectural innovation of mainshaft elimination and the structural advantages of three-row cylindrical rollers, provides a viable technical path for the industry.
Key points:
Architectural innovation: Replacing the traditional “dual bearings plus mainshaft” combination with a three-row cylindrical roller main bearing achieves mainshaft elimination, reduces drivetrain weight by more than 50%, significantly shortens the axial dimension, and adapts to compact nacelle space.
Comprehensive performance superiority: Outperforms TRB/DTRB in all six dimensions — load-carrying capacity, structural stiffness (nearly 50% higher than TRB), installation difficulty (direct bolt fixing), transmission efficiency (94%–97%), reliability (no batch failures for more than 20 years), and comprehensive cost (20% reduction in life-cycle cost).
Fully verified reliability: Rigorous laboratory testing (deformation, load limit, and service life all meeting the highest industry standards) and European field project verification (including offshore strong impact and high salt spray environments) provide dual confirmation of reliability.
Solution value beyond a single bearing: What JUNHUAN provides is not a single bearing component but an overall solution optimized at the drivetrain architectural level. Its design capability, technical accumulation, and full life-cycle service value far exceed those of traditional single bearing suppliers.
As the global installed wind power capacity continues to grow and the trend of turbine upscaling becomes irreversible, the technical upgrading of the main bearing — as the load-bearing core of the drivetrain — is imperative. With its load-carrying capacity, reliability, compact structure, and life-cycle economy, the JUNHUAN three-row cylindrical roller main bearing solution is becoming a key technical path for breaking through the bottleneck of wind turbine upscaling.