Abstract
The resistivity of oil impregnated paper will decrease during its aging process. This paper takes paper resistivity as an assessment index to evaluate the insulation condition of oil impregnated paper in power transformer. The feasibility of this method are discussed in two aspects: reliability and sensitivity. Iterative inversion of paper resistivity was combined with finite element simulation. Both the bisection method and Newton’s method were used as iterative methods. After the analysis and comparison, Newton’s method was selected as the first option of paper resistivity iteration for its faster convergence. In order to consider the spatial distribution characteristic of paper aging and enhance the calculation accuracy, the resistivity calculation is expanded to a multivariate iteration based on Newton’s method, in order to consider the spatial distribution characteristic of paper aging and improve the calculation accuracy. This paper presents an exploratory research on condition assessment of oil impregnated paper insulation, and provides some reference to the security and economy operation of power transformers.
Highlights
As the main dielectric media in oil-immersed transformers, the oil and oil impregnated paper will degrade with time, under thermal, electrical, chemical stresses and other factors [1,2,3,4]
Different paper resistivity values are applied to paper at different positions as shown in Figure 11 and Table 2
The resistivity of oil impregnated paper will decrease during its aging process
Summary
As the main dielectric media in oil-immersed transformers, the oil and oil impregnated paper will degrade with time, under thermal, electrical, chemical stresses and other factors [1,2,3,4]. The electrical diagnostic methods mainly rely on the comparison between measured data and historical data, and may be influenced by the geometry [32] Among these methods, there is no unified assessment index currently available for different types of transformers. Changes in the moisture and oil contents during the aging process lead to changes in the dielectric properties of paper These changes are the fundamental basis of all electrical diagnostic methods [28,32,35,36]. The resistivity of paper will decrease over time as the moisture content and aging increase [28,34], the resistivity of paper can be used to assess the insulation condition of oil impregnated paper. Non-uniform ageing was considered in the iterative method to improve the accuracy of the resistivity calculations
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