Mechanical Performance Analysis and Research on New Methods for Online Non-Destructive Evaluation of Glass Fiber Reinforced Plastic Connectors in Converter Valves
Zhang Xinlong1, Zou Yansheng2, Cheng Li1, Tao Bo1, Liao Ruijin1
1. State Key Laboratory of Power Transmission Equipment Technology Chongqing University Chongqing 400044 China; 2. Electric Power Research Institute EHV Company of CSG Guangzhou 510530 China
Abstract With the increase in operation time of high-voltage converter valves, there has been a significant issue of surface cracking observed in a large number of glass fiber reinforced plastic (GFRP) connectors. However, currently, there is limited research on the actual mechanism of GFRP connector cracking within converter stations, and the long-term mechanical performance remains unclear. Meanwhile, the assessment of its mechanical properties presently relies mainly on destructive offline testing, without the ability to accurately characterize its mechanical performance through online non-destructive testing methods. Acoustic emission (AE) methods enable real-time dynamic inspection of microcracks and represent a potential non-destructive testing method for evaluating the mechanical performance of GFRP equipment online. This paper investigates the cracking mechanism of GFRP connectors and employs acoustic emission technology to assess the residual mechanical strength of GFRP connectors. The results show that creep failure under long-term loading is the cause of physical damage to GFRP connectors; the evaluation mechanical performance of cracked GFRP connectors obtained through acoustic emission technology closely matches actual test results, with an error range of 1% to 3%. Firstly, physical and chemical tests were conducted on both new and cracked GFRP connectors. The experimental results indicate that compared to the new GFRP connectors, the cracked ones do not exhibit significant chemical aging or thermal decomposition. However, they do present internal defects such as fiber breakage, matrix cracking, and fiber-matrix interface debonding, leading to a substantial decrease in mechanical performance. It was preliminarily confirmed that physical damage caused by mechanical stress is the primary reason for failure. Subsequently, a three-dimensional simulation model of the GFRP connectors was established using Ansys software. Simulation results indicate that under actual working conditions, the stress on the GFRP connectors is mainly concentrated at the actual crack locations, with the maximum stress reaching 47.3 MPa, exceeding their maximum load capacity (43.5 MPa), resulting in crack failure in that area. Additionally, the maximum stress exceeds 30% of the bending strength (122.3 MPa) of the GFRP connectors not yet in operation, meeting the premise of GFRP creep failure behavior, further validating that the cracking of GFRP connectors is caused by mechanical reasons. Finally, samples with different residual mechanical strengths were prepared through mechanical aging tests of varying durations. A weak acoustic signal detection platform was established, and the samples were subjected to acoustic emission loading tests using this platform. The results of the acoustic emission loading tests show that there was no significant change in the residual mechanical strength of the samples before and after the tests, validating the non-destructive nature of acoustic emission detection method. Furthermore, under low-load conditions, the hit count rate increased approximately linearly with time, and the residual mechanical strength of the samples decreased linearly with the increase in hit count rate, with the slope and intercept of the negative linear relationship having an exponential relationship with the applied load. By utilizing the negative linear relationship between residual mechanical strength and hit count rate, the residual mechanical strength of cracked GFRP connectors can be quantitatively calculated. Compared to actual test values, the error range is only 1.4%~3.2%, indicating that acoustic emission detection technology is feasible for online evaluation of GFRP connectors.
Zhang Xinlong,Zou Yansheng,Cheng Li等. Mechanical Performance Analysis and Research on New Methods for Online Non-Destructive Evaluation of Glass Fiber Reinforced Plastic Connectors in Converter Valves[J]. Transactions of China Electrotechnical Society, 2025, 40(7): 2033-2042.
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