Study On Oil-Paper Insulation In Transformer Based On Return Voltage Measurement

Oil-immersed power transformers are important equipments in power system substations, which are the core of the energy conversing and transferring. The security of the system is decided directly by the operation state of Oil-immersed power transformers. The Existing diagnostic methods for the state of oil-immersed power transformers are not sufficient, comprehensive and reliable. Return voltage method, a new non-destructive, anti-interference detection method, can reflect the oil-paper insulation information.However, none corresponding relationship between the state of oil-paper insulation and return voltage test results has been established around the world, there isn't a very accurate interpretation of the insulation condition of oil-paper. In this paper, the impact of recovery voltage test results by various factors is systematic studied on the basis of simulation, laboratory testing and field test, and the relevance between return voltage measurement results and other methods is also systematic studied.First, a simple model of oil-paper insulation system is builded under MATLAB/SIMULINK environment. The return voltage measurement results is studied by the changing of the charging voltage, charging time and defferent parameters in the model (to simulate different insulating state). It is proved that the maximum return voltage had a linear relationship with the charing voltage, and the influence can be eliminated by appling the same charging voltage; Moreover, different insulation states have different return voltage peak values which have some relation with the charging time and the polarization time constant; In addition, the return voltage curves will be distorted when the charging time is too long.Second, return voltage test system is set up to study the water content, insulating oil quality and the aging time's impact on the test results of return voltage measurement in the laboratory. It is proved that return voltage parameters and water content in the insulation system showes a good fit of quadratic function; Return voltage method is effective to assess oil quality of insulation system qualitatively. Furthermore, it can assess the insulation condition of transformer oil by comparing the measured polarization spectrum curves.Finally, the tests of return voltage measurement on many typical transformers which operated in power stations are analyzed. Results show that the aging has greater impact on the return voltage test results than the moisture content in insulation system.As the center time constant is sensitive on aging particularly, it can be used to. diagnose the oil-paper insulation state of the transformers.The maximum value of return voltage is relative to the capacity of transformers. Return voltage test results shows a good linear relationship with the logarithm of furfural content. Meanwhile the degree of polymerization value, molecular weight, the gas in oil and other test results also have good correlation with recovery voltage test results.