Installation of cross-linked polyethylene (XLPE) cable joint possibly introduces defects into the XLPE-silicon rubber interface, such as micro-cavity and micro-wire. Those defects greatly decrease the interfacial breakdown strength and endanger the stability of power system. However, the traditional method only measures the breakdown strength, which alone is limited and can not provide detailed information to more clearly understand the dielectric performance and tracking failure mechanism. This paper investigated the effect of micro-cavity on tracking failure by analyzing the distribution characteristics of discharge light and carbonization. Interfaces with those defects were setup by pressing together a slice of XLPE and a slice of transparent silicon rubber. A 50 Hz AC voltage was applied on a pair of flat-round electrodes sandwiched at the interface with their insulation distance of 5 mm until tracking failure occurred. The evolution of both discharge light and carbonization at the interface from discharge to the failure was recorded with a video recorder and then their channel width was analyzed with image processing method. Obtained results show that micro-cavity at an XLPE-silicon rubber interface strengthens the transportation of charge and easily leads to interfacial discharge and tracking failure. The distribution of discharge light and carbonization at the interface with micro-wire proves this.
Imaging processing method was adopted to investigate the effect of silicon grease on tracking failure of the XLPEsilicon
rubber interface by analyzing the distribution characteristics of discharge light and carbonization at the interface.
Three interfaces were set up by pressing together a slice of XLPE and a slice of transparent silicon rubber. One filled
silicon grease and the other partly filled the grease. As comparison, the third one filled on grease. High voltage (AC 50
Hz) was applied on a pair of flat-round electrodes sandwiched at the interface with their insulation distance of 5 mm.
When the test voltage was raised to a certain value, discharge occurred and discharge light appeared and carbonization
accumulated at the interface. The discharge light from discharge to the failure and the carbonization after the failure was
recorded with a digital video recorder and then the images were analyzed with image processing method. Obtained
results show that silicon grease at the interface weakens the transportation of charge and enhances the interfacial
breakdown strength. However, interfacial discharge and tracking failure easily occur once discharge appears. Image
processing method is helpful to understand the tracking failure process and mechanism of XLPE cable joint.
Blood pressure reflects a person's health.It is proposed here that the method of detecting blood pressure may be the key to improving the precision of blood pressure measurements. The oscillometric blood pressure measurement technique is widely used in automatic blood pressure measurement instruments correctly. A method of blood pressure measurement by oscillometric method is first presented. In the oscillometric method, the basic principle of the "feature point" method and the "amplitude characteristic ratios" method is also explained and discussed here. A new method of blood pressure measurement, namely the coefficient difference comparative method, is proposed here,which is based on the feature point method and amplitude characteristic ratios method. The method is proved both effective and reliable through the analysis of many cases and clinical tests. Utilizing Visual C++, software for this new and novel method was developed and passed criterion simulation apparatus test. When applied in hospital situation, its error was ±5%. It is concluded that the oscillometric blood pressure measurement method can provide better means of blood pressure measurements reference for doctors.
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