Study On Connection Condition Monitoring For A Prefabricated Sectional Wind Turbine Blade Specimen With PZT

Faced with increasingly severe energy shortage and environmental pollution, the utilization of wind power as a renewable and clean energy has received global attention. To adapt to the rapid growth in wind turbine power, the length of wind turbine blade has increased significantly to improve the wind–catching ability. In the construction of wind farms in southern mountainous areas of China, the transportation of integral blade is a risky task and requires large investment in road quality improvement. A FRP(fiber reinforced plastic) wind turbine blade can be prefabricated in several segments and then connected by high strength prestressed bolt on site, which can effectively solve the problem and lower the road quality standards. However, compared to conventional integral blade, the reliability of the connection part is crucial to the safe functioning of the blade, an effective monitoring approach for this new kind of prefabricated blade is required. Effective attempts have been made aiming at the detection of FRP wind turbine blade, but monitoring approach made specifically for prefabricated wind turbine balde is yet absent. In recent years, PZT(piezoelectric ceramics) based structural health monitoring technology have wide application, in this paper, a monitoring method based on wave propagation theory is proposed to detect the connection status of the prefabricated turbine blade. The specific work can be concluded as in following aspects.(1) Based on the physical characteristic of PZT(lead zirconate–titanate), the production and installation of PZT transducers are introduced. The monitoring system is tested in advance, which is proven to have good response and linearity.(2)A type of prestressed bolt–connected sectional fabricated wind turbine blade designed for a large–scale wind turbine is introduced. The monitoring arrangement for the experiment based on wace propagation of various signal input is introduced.(3)An experimental study is conducted on the monitoring of the scaled model of unit–width sectional wind turbine blade. The PZT transducers adhere to the surface of the blade connection units are used as actuators and sensors respectively, the connection unit specimen is at first tightened by prestressed bolt and then gradually damaged under incremental axial tensile force act at both ends of the specimen. The characteristics of output signal under continuous and sweep sinusoidal signal excitations are compared and corresponding health index is proposed. In analysis of the health index, the connection status can be determined, which further verified the effectiveness of the proposed method in connection status monitoring of the prefabricated sectional blade.(4)A montoring method based on FRF(frequency response function) is proposed. The pulse excitation signal is first generated by a hammer and the output signal received by PZT transducers. By analyzing the frequency response function of output signal in appropriate frequency range, the connecton status of the sectional blade is successfully monitored.