Study On Return Voltage Measurement For Diagnosing Oil-Paper Insulation In Transformer

Oil-immersed power transformer is the core and key position of electrical transmission and distribution, and the most important and vital part of electrical net as well. Mastering its condition of insulation accurately and avoiding any problems resulting in the break of electrical transmission, even serious accidents such as large area power cut is very meaningful. At present, there are lots of methods diagnosing insulating condition of oil-immersed power transformers, but each of them has its drawbacks. RVM(return voltage measurement) containing plenty of great information such as ageing extent, water content in paper and so on is not sensitive to disturbs, and a non-destructive method as well, as a result, it can be well used for transformers'condition diagnosis, So, it has been got much interest recently. But because of its late research, there are many things still not known, a case in point is that how RVM reflects oil-paper insulation condition, so more researches should be done to solve these questions.In this paper, on the basis of summarizing the got results of diagnosing ageing condition of oil-paper insulation system both in domestic and overseas, the point that ageing of oil-paper insulation system will change its dielectric response can be got by way of analyzing ageing mechanisms of insulating oil and insulating paper. Dependences of parameters of RVM on different parameters in circuit are researched via simulink. Hot accelerated ageing tests are done on oil-paper samples, and so do RVM, the changing regularities of parameters of RVM at different conditions are researched.So in this paper, by way of simulink and test, the following conclusions can be got.1. The ratio of charging time to discharging time (tc/td) has a great influence on the parameters of RVM, tc/td has an exponential relation with Urmax and Si, and has an power relation with tcdom. So, proper tc/td should be determined before test. Charging voltage U0 has also a great role on the parameters of RVM, U0 has a linear relation with Urmax and Si, tcdom doesn't change regardless of how many U0 is. Extended debye model can be used to simulate dielectric response properties of oil-paper insulation system. 2. Relatively stable value reflecting the information of the latter part of RVM (reflecting factors with slower polarization velocity) can be used as one of parameters of RVM.3. Both the temperature of insulation system and layers of insulating paper have a great influence on parameters of RVM. The temperature of insulation system has an exponential relation with parameters of RVM, and so do layers of insulating paper.4.DP has a linear relation with parameters of RVM, water content in paper will change the changing velocity of RVM.