Investigation Of Ultrasonic Spectral Analysis Technology To High-voltage Aluminum Electric Porcelain

High-voltage insulator of porcelain, which is called insulator for short in this paper, takes an important position in transmission line and it is important component of the transmission line and substation, too. For there is a close relationship between insulator's properties and electric porcelain which is the main part of insulator, electric porcelain testing for getting good insulator become very important. Compare with the way of destructive testing, ultrasonic nondestructive characterization and evaluation has gained greater attention for obvious superiority and the latent application prospects. However, electric porcelain material is complex and multiphase mixture, its ultrasonic attenuation mechanisms is hard to quantify. At the same time, it is difficult to control structure of electric porcelain during production. Therefore, the research of ultrasonic characterization of insulator has been focused on crack inspection and material aging, and ultrasonic characterization research of structure of insulator is scarce.In this paper, the immersed line focus pulse-echo technique is developed for electric porcelains with sintering temperatures of 1220℃,1260℃and 1300℃, and one testing system of electric porcelain rod is set up. First, the ultrasonic longitudinal velocity was measure to electric porcelains with various sintering temperature by the immersed focus technique. It is found that longitudinal velocity gradually increase with a rise in sintering temperature, but, when sintering temperature approaches a temperature, velocity increase rate tend to even out. Then the immersed line focus pulse-echo technique is applied to obtain echo signals of electric porcelains with various sintering temperature. The pulse-echo signal'normalized power spectrum is compared according to the ultrasonic spectral analysis techniques. The main results are as following:when probe detecting frequency is 1MHz, there is a distinct peak in 0.580MHz for electric porcelains with sintering temperature of 1220℃and the sub peaks appear at 1.282MHz and 1.495MHz. There is a peak in 1.495MHz for electric porcelains with sintering temperatures of 1260℃and 1300℃. At the same time, amplitudes of normalized power spectrum gradually increase with a rise in sintering temperature when peak frequency is 1.495MHz. And when probe detecting frequency is 2.5MHz, the high peak frequency all appear at 3.91 MHz for electric porcelains with various sintering temperatures, and there are sub peaks in 4.09MHz and 4.30MHz. Amplitudes of peaks of electric porcelains with 1220℃are higher than electric porcelains with 1260℃and 1300℃.It could be concluded that three kinds of electric porcelains with various sintering temperature can be identified by normalized power spectra when probe's frequency is 1.0MHz. Further analysis reveals that corresponding to different temperatures, the amplitudes of peaks of normalized power spectra fluctuate around their average values. In fact, the values of amplitudes form a fuzzy set corresponding to temperatures. In this paper, closeness degree of fuzzy pattern recognition was used to evaluate the approaching degree among the fuzzy sets. Greater closeness degree corresponds to closer sintering temperature between the reference samples and the analysis samples. Besides, the over firing and incomplete firing electric porcelains can be sorted from electric porcelains which sintering temperature are supposed same temperature by adopting calculation of closeness degree, so as to guarantee quality of insulator.