VLF电压试验电压幅值与试验时间的优选

VLF电压试验电压(UT)和试验时间(tT)的选取直接影响到有效地发现绝缘缺陷的概率,但目前电力电缆线路VLF电压试验时如何选取UT和tT仍无明确结论。1980年以来各国标准规定值差异很大,试验的有效性和等效性尚在探讨之中,目前一般取UT=2~3.5U0(U0为相电压),tT=15~60 min。长期积累的运行经验和理论及试验研究证实,延长tT和提高UT将对电缆介质造成不可逆损害,导致介质早期击穿。因此结合国内外现场和试验室研究结果并采用数理统计分析的方法优选了VLF(0.1 Hz)UT和tT。结果表明:UT=3U0时,tT取40 min,基本能够满足电力电缆线路绝缘品质判别的现场试验要求。

Optimizing Validation of Voltage and Time for VLF(0. 1Hz) Voltage Testing

VLF(0.1Hz) voltage test as one of the quality evaluation methods has been applied to medium voltage capacitive equipments,i.e.electrical generators,electrical motors and power cable lines for more than 20 years.Until today,it has been disputed that how to validate the test time and test voltage when taking VLF voltage test on power cable line because the different probability of identifying faults hidden in dielectric in advance by the test effectively.The validity and equivalence of these test results have been researched and discussed since 1980's.Unfortunately,the test results are not obvious evidence.In fact,the technical standards of VLF voltage test including test voltage range from 2U_0 up to 3.5 U_0 and test time range from 15 min up to 60 min are confirmed by different countries in the word.Practice experience in field and many results of theoretical research as well as parallel tests in laboratory in China have proved that extending test time and increasing high voltage are not necessary and very harmful to dielectric of power cable due to the power cable using high resistive solid dielectric.Even the damage of power cable dielectric is not rehabilitated and lead power cable line early or unexpected broken.Therefore,it is important to optimize the combination of test time and test voltage of VLF(0.1Hz) voltage test today.For optimizing validation of test voltage and test time,the validity and equivalence as well as relation of test voltage and test time of VLF(0.1Hz) voltage test is discussed and analyzed in detailed by mathematic statistics based on a mass of test experience in field and in laboratory in this paper.The results of research and optimization in the paper prove and verify that the test method of 3U_0 test voltage and 40min test time is much better fit for power cable lines in field test,and may meet the estimation of dielectric quality of power cable lines on-site testing.