Research On Phased Array Ultrasonic Detection And Online Model Monitoring Test Of Cracks In Pitch Bearings Of Wind Turbine In Service

As an important part of clean energy,wind power generation is developing rapidly and is a key part of achieving the "double carbon" goal and moving towards green development.As a key component of wind turbine pitch system,the pitch bearing is subjected to axial force generated by centrifugal action and radial force generated by the action with the hub during service,which is prone to fatigue cracks,and the expansion of cracks may lead to pitch bearing fracture,blade fall and other serious consequences.Effective non-destructive testing methods can detect the cracks at the early stage of cracks and repair or replace the pitch bearing in time to avoid serious consequences.Due to the complex structure of the pitch bearing and the limited inspection space caused by the special service environment,the conventional inspection methods cannot effectively detect the in-service pitch bearing.For the shortage of conventional inspection,this project adopts phased-array ultrasonic inspection method to detect the cracks of wind turbine pitch bearings.In-service pitch bearing cracks occur at the root and bolt holes,and different detection schemes are proposed for the cracks at different locations,taking into account the structure and service environment of the pitch bearing.Among them,the cracks at the root of the tooth were detected by phased-array ultrasonic sector sweep;the cracks near the bolt hole were detected by direct-fire method and deflection method on the basis of sector sweep.According to the needs of the inspection program,the factors affecting the phased-array ultrasonic inspection are analyzed,and the main research is on the influence law of the phased-array ultrasonic inspection probe characteristic parameters,including the excitation frequency of the inspection probe,the number of wafers and the size of the wafers,on the phased-array ultrasonic inspection,and the experience of phased-array ultrasonic inspection is combined to determine the range of values of the inspection probe characteristic parameters.CIVA software was used to simulate three inspection schemes,namely,phased-array ultrasonic sector sweep,deflection method and direct-fire method,to explore their feasibility.The phased-array ultrasonic inspection simulation was performed on the three-dimensional simulated body of the pitch bearing,and the optimal feature parameters such as excitation frequency,number of array elements and array element size applicable to the in-service wind turbine pitch bearing inspection probe were obtained through the simulation of the detection of transverse hole defects according to the range of the detection probe feature parameters;the feasibility of the scheme to detect cracks was verified through the simulation of rectangular defect detection and response analysis.The production of special inspection tooling,comprehensive analysis of phased-array detection errors,proved the applicability of phased-array ultrasonic sector sweep and direct-fire method in the actual detection,while the deflection method is not yet available for actual detection due to insufficient built-in algorithms of the instrument.The detection sensitivity of 0.2mm was determined based on the shallowest depth of rectangular groove that could be detected.The location accuracy of the direct-fire method is 97.8% and the dimensional accuracy is 96.3%.A phased-array sector sweep was used to inspect the naturally cracked pitch bearing and clarify the defect display of natural cracks.On the basis of the crack detection method at the tooth root,a special detection device integrating probe,scanner and encoder is designed based on the service environment of the pitch bearing,which realizes automatic detection and online monitoring of the pitch bearing during pitch change.