English Views: 68 Author: Site Editor Publish Time: 2026-03-30 Origin: Site
In-depth Analysis of Disc Spring Application in Wind Turbine Pitch System: Solving Fatigue Challenges Under Frequent Start-Stop Operations
Driven by the dual carbon goals, the wind power industry is entering a golden era of large-scale development. As the core control component of wind turbines, the pitch system directly determines generator efficiency and operational costs. Disc springs, with their high rigidity, minimal deformation, and substantial load-bearing capacity, serve as critical elastic elements for braking and cushioning in pitch systems. However, wind pitch systems face complex operating conditions including sudden wind speed fluctuations, directional changes, and grid instability, making fatigue failure from frequent start-stop cycles a persistent industry challenge. This study examines a real-world case from a 5MW wind farm to analyze fatigue failure mechanisms in wind pitch systems, proposing comprehensive solutions covering material selection, design optimization, manufacturing processes, and operational maintenance.
The pitch system serves as the wind turbine's attitude regulator, dynamically adjusting blade pitch angles in real-time to achieve wind speed adaptation, power stability, and safe shutdown. The braking system performs dual functions of emergency braking and precise positioning, requiring millisecond-level response to rapidly lock pitch bearings and prevent blade overspeed rotation or drift. The disc spring acts as the core power source for the braking system, providing stable braking force through preload while cushioning start-stop impacts.
Safety brake: The disc spring assembly provides continuous preload force to achieve reliable locking of the pitch bearing, enabling rapid braking in emergency situations and ensuring unit safety.
Buffer compensation mechanism: Absorbs impact loads transmitted by blades during pitch variation, compensates for thermal expansion/contraction and installation errors, and prevents rigid impact damage to transmission components.
The pitch control system must complete dozens of start-stop cycles daily, accumulating over 15,000 cycles annually. The disc springs are subjected to prolonged superimposed alternating and impact loads, resulting in particularly severe fatigue failure issues.
Elastic attenuation: Insufficient preload due to long-term cyclic loading leads to weakened braking effect
Crack initiation: Microcracks form at stress concentration areas during high-frequency compression-rebound cycles
Plastic deformation: Permanent deformation of disc springs caused by overload impact directly leads to brake failure
Soaring O&M costs: Replacing disc springs for a single wind turbine now exceeds 50,000 yuan, resulting in a 15%-20% annual increase in wind farm maintenance expenses.
A wind farm in Northwest China has an installed capacity of 50MW, equipped with 10 5MW doubly-fed wind turbines. The system employs an electric pitch control system, with disc springs used in pitch brakes. Each turbine unit is configured with 12 sets of disc spring assemblies (each set consisting of 10 stacked springs). The wind farm experiences an average annual wind speed of 6.8m/s, with extreme wind speeds reaching 28m/s. Winter temperatures drop to 25°C, resulting in complex operating conditions and frequent start-stop cycles.
Two years after commissioning, the unit successively experienced faults such as insufficient brake pressure and failure to achieve rapid blade locking. Disassembly inspection revealed significant elastic attenuation in the disc springs, with cracks appearing on the end faces of some springs. Through on-site testing and laboratory analysis, the core causes of failure were identified as follows:
Inappropriate material selection: The original disc spring was made of ordinary 60Si2MnA steel, which exhibited insufficient fatigue resistance and reduced low-temperature toughness.
Unreasonable design parameters: Incorrect stacking method resulting in uneven force distribution, with local stress concentration coefficients reaching 1.8
Process defect: Shot peening reinforcement was not applied, resulting in machining tool marks on the surface, which serve as fatigue crack initiation sites.
Lack of operation and maintenance: No status monitoring mechanism has been established, resulting in inability to provide early warnings for fatigue damage.
During the start-stop operation of the pitch control system, the disc spring undergoes alternating cycles of compression and rebound, with average stress approaching 80% of the material's yield strength. Emergency start-stop operations subject the spring to impact loads that elevate stress amplitude to 1.5 times the rated value. Stress concentration coefficients at the disc spring's end face, inner bore, and chamfered areas reach 1.5 to 2.0, making these regions critical for crack initiation.
Through transmission electron microscopy (TEM) and backscatter electron diffraction (BSEED) analysis, dislocations within the disc spring continuously slip and entangle under alternating loads, forming microplasticity zones. Element concentration at grain boundaries reduces dislocation motion resistance, allowing microcracks to propagate along these boundaries. Long-term cyclic loading leads to nanoscale carbide precipitation, further compromising fatigue resistance.
Temperature effect: Material toughness decreases in low-temperature environments, making impact loads more prone to induce brittle fracture.
Vibration coupling: Superposition of operational vibration and pitch start-stop vibration exacerbates micro-wear in wind turbines
Poor lubrication: Dry friction leads to surface wear, resulting in stress concentration and shortened fatigue life.
Considering the low-temperature and frequent start-stop operating conditions in wind farms, 55CrSi spring steel was selected and treated with a two-phase zone pre-cooling + graded quenching process. Tests demonstrated that disc springs fabricated from this material exhibited a stiffness decay rate below 3.5% after 20,000 hours of service under alternating temperature ranges of 25°C to 40°C, significantly outperforming the original material's 9.2% stiffness loss.
Based on the GB/T 1972.12023 standard 'Disc Spring', redesign the disc spring parameters:
Optimize the aspect ratio (h/t) from 1.2 to 1.3 to reduce stress concentration coefficients
The chamfer radius for the inner hole and end face increases from 0.1 mm to 0.3 mm.
The stacking method was optimized to opposite stacking. Finite element analysis showed that the maximum stress was reduced by 30%.
Through blade pitch shaft load simulation, the optimal preload force was determined to be 25 kN.
Shot peening reinforcement: Utilizing robotic automated shot peening to form a residual compressive stress layer on the disc spring surface, resulting in a fatigue life improvement of more than 3-fold.
End face treatment: The flatness of the end face shall be controlled within 0.005 mm to avoid bending deformation caused by eccentric loading.
Surface protection: Utilizes molybdenum disulfide + polytetrafluoroethylene (PTFE) lubricating coating, reducing the friction coefficient from 0.35 to 0.08.
Installation specifications: Use dedicated guide fixtures to ensure coaxiality of disc springs, with preload force error controlled within ±5%.
Micro pressure sensors and temperature sensors are installed at critical positions of the disc spring assembly to monitor preload force and temperature changes in real time. A first-level warning is triggered when the preload force drops below 22kN, while a second-level warning is activated when it falls below 20kN, prompting scheduled shutdown for replacement. By integrating deep learning algorithms to analyze the correlation between load characteristics and damage progression, precise fatigue life prediction is achieved.
Establish a monthly inspection and annual disassembly system, with additional specialized inspections conducted after extreme weather events. Adopt a batch management + lifespan tracking model to record the installation time, operational parameters, and fault logs of each disc spring, enabling precise replacement and avoiding cost wastage caused by blind replacements.
The wind farm completed full-system optimization and retrofitting in Q1 2024, with six months of operational validation following implementation.
The frequency of disc spring-related failures decreased from 23 times per month to zero.
The stiffness decay rate of the disc spring is controlled within 3%, and the preload retention rate exceeds 97%.
Operating costs reduced by 40%, with a 3% increase in power generation
The expected service life of single-disc springs has been increased from 2 years to 8 years.
The application of disc springs in wind turbine pitch systems requires moving beyond conventional single-type selection approaches and establishing a comprehensive solution encompassing material design, process monitoring, and operational maintenance.
Materials form the foundation: Select precise models based on operating conditions, prioritizing special spring steels with fatigue resistance and low-temperature tolerance.
Design is the core: Strictly adhere to national standards, optimize structural parameters and stacking methods, and eliminate stress concentration.
Process is critical: Shot peening reinforcement and surface protection processes directly determine the fatigue life of disc springs
Monitoring serves as a safeguard: Intelligent monitoring enables early warning of fatigue damage, transforming passive maintenance into proactive prevention.
Operation and maintenance (O&M) serves as the foundation: Establishing a full-cycle O&M system to extend the service life of disc springs
Jiangsu Sunzo Spring has long been dedicated to the R&D and manufacturing of high-performance disc springs, accumulating extensive engineering expertise in the wind power sector.
Material system: Offers multiple material options including 60Si2MnA, 50CrVA, 55CrSi, and Inconel, suitable for various operating conditions.
Design capability: Parameter optimization and finite element analysis based on the national standard for disc springs to accurately match load requirements
Process Assurance: Equipped with advanced production lines including automated shot peening, precision grinding, and lubrication coating technologies.
Technical Support: Provides end-to-end services ranging from selection calculations and sample testing to on-site installation guidance.
For wind turbine pitch system disc spring selection or customized solutions, please contact our sales team for details.
