换流阀冷却系统均压电极结垢超声导波检测方法研究

Investigation of ultrasonic guided wave mode conversion characteristics in grading electrodes sediments detection of the HVDC converter valve cooling system

换流阀冷却系统中均压电极结垢检测是直流输电系统安全运行的必要保障。当前人工筛查的检测方法,有较大的盲目性且易造成系统漏水等故障。因此提出基于超声导波回波特性的在线结垢检测方法。选取频散小、传输距离长的L(0,2)模态导波作为激励信号,将电极结垢视为多孔介质并计算其特征参数,构建了流-固-声多物理场作用下的均压电极结垢检测模型,确定了最佳超声激励频率并仿真研究了0.2~1.0 mm厚度水垢对声波信号的反射与吸收特征,分析了L(0,2)模态导波与水垢交互过程中的模态转换过程,进而搭建实验系统,开展了水垢厚度为0.1~0.8 mm的实验验证工作。实验结果表明,基于L(0,2)超声导波回波特性的在线结垢检测精度达0.1 mm,为换流阀均压电极结垢检测提供了一种有效的方法。

Sediments detection on the grading electrodes installed in the inner cooling system is the necessary part to ensure safe operation of the high voltage direct current(HVDC)converter valve.At present,the sediments detection of the grading electrodes mainly depends on manual screening,which has great blindness and is easy to cause system leakage and other faults.To address these issues,an online sediments detection method based on the echoing characteristics of ultrasonic guided wave is proposed.The L(0,2)mode guided wave with low dispersion and long transmission distance is selected as the excitation signal.Sediments of electrodes are considered as porous medium and the characteristic parameters are calculated.Then,a fluid-solid-acoustic multi-physical field simulation model of sediments detection is formulated,and the optimum excitation frequency is determined.The reflection and absorption characteristics of 0.2~1.0 mm thick sediments on acoustic signals are simulated.The mode conversion processes in the interaction between the longitudinal L(0,2)mode and sediments are analyzed.Finally,the experimental system is established to verify the actual detection accuracy in the sediments thickness of 0.1~0.8 mm.Experimental results show that the accuracy of online sediments detection method based on the echoing characteristics of ultrasonic guided wave is up to 0.1 mm,which demonstrates the online sediments detection method is effective for sediments detection with grading electrodes of the HVDC converter valve cooling system.