用于复合绝缘子伞裙老化无损检测的单边核磁共振方法

Non-destructive Aging Detection Method for Silicone Rubber Insulator Shed Based on Unilateral NMR Principle

硅橡胶复合绝缘子在中国电力系统中的用量逐年增加。对复合绝缘子老化状态的评估和监测关系到电力系统的安全运行。提出了一种单边核磁共振测量方法,实现对复合绝缘子伞裙老化状态的无损检测。研究主要包括核磁共振传感器设计及其信号分析两部分。使用有限元算法设计出一种半椭圆环状的单边核磁共振磁体,在磁体外部10 mm×10 mm×4 mm的测量区域内,建立了3.9 T/m的近似恒定梯度磁场。使用该静态梯度场,实现了伞裙材料的分层老化检测。该研究以3种不同运行时间的绝缘子为测试样品,使用CPMG序列激励样品,并对核磁共振回波信号峰值包络线进行一维横向弛豫时间的反拉普拉斯变换,从反演谱中提取出等效横向弛豫时间T2eff,实验表明:随着复合绝缘子老化程度加剧,T2eff减小;对于同一复合绝缘子,其T2eff由里及表,逐渐减小。所提出的等效横向弛豫时间T2eff能够表征复合绝缘子伞裙的老化程度,为评价其老化提供了一种无损检测的新方法。

Silicone rubber insulator is widely used in the power system, the assessment and monitoring of its aging status are critical to the safe operation of the power system. This paper presented a non-destructive unilateral nuclear magnetic resonance（NMR） method to measure the aging status of silicon rubber insulator. The research included two parts： the design of the NMR sensor, and the analysis of the NMR signal. The magnet of the NMR sensor with a semi-elliptical structure was designed by finite element methods. A static magnetic field with constant gradient of 3.9 T/m was built in the measurement area with a size of 10 mm10 mm4 mm. With this gradient field, the detections of various depths into the insulator shed were realized. Three groups of insulators with different service times were measured, and the CPMG sequence was employed to excite the samples. By performing the Inverse Laplace transform to the peak-envelope curve of NMR echoes, the one dimensional distribution of transverse relaxation time was obtained. From the one dimensional distribution, the effective transverse relaxation time T2 eff was extracted. It demonstrates that： T2 eff decreases as the service time of the insulator increases; T2 eff decreases as the measurement moves from the middle part to the surface of the shed. T2 eff can reflect the aging status of the silicone rubber insulator shed. The result can provide a new non-destructive detection method for assessing the aging level of the composite insulator.