Determination of individual values of four-element equivalent circuits elements parameters at technical diagnostics of insulation by absorption methods

Abstract

The aim of this article is to present a methodology of determining of the individual values of the parameters of four-element equivalent circuits for insulation with through conductivity. Methodology. The proposed method consists in the fact that at a time interval of more than 10 s, when the charge indicator no longer contributes to the leakage current, three points t1, t2 and t3 are selected, such that t2 – t1 = t3 – t2. To be able to determine the absorption coefficient R60/R15, it is recommended to take t1 = 15 s, t2 = 37.5 s and t3 = 60 s. At the same time, by subtracting I(t2) – I(t1) and I(t3) – I(t2), the constant component of the absorption curve is excluded and it becomes possible to determine the individual values of the parameters of the generalized equivalent circuit of insulation, additionally using its conductivity in operator form. Results. As calculations show, the correct determination of the parameters of insulation equivalent circuit according to the proposed method is possible only with a certain ratio of these parameters. The charge time of the geometric capacitance Cg(R0+Rd), where R0 and Rd are the resistance that forms the charging exponent, and the resistance of the sensor, should be within 0.2 s <Cg(R0+Rd)<1 s, the time constant CaRa, where Ca and Ra are the capacitance and resistance of the absorption chain, should be more than 3 s, the product of CgRl, where Rl is the leakage resistance, more 0.5 s, the leakage resistance Rl is less than the absorption resistance Ra. Checking the methodology on a model example gives the values of the parameters of the insulation equivalent circuit that match the specified ones with high accuracy. Practical value. The use of individual values of the parameters of insulation equivalent circuits when applying absorption diagnostic methods with considering the time values and dimensional factors, allow to calculate all currently used diagnostic parameters, to determine the conditions of certain insulation types, as well as in more detail, in comparison with the existing approach, to assess the technical condition of the insulation and the reasons of its changes.