On the Development of the Theory of Resonant Processes in Power Transformer Windings. Part 3. Transients in a Circuit with Two PI Sections

Abstract

The development of electrical networks and widely used technical solutions lead to more frequent winding insulation failures in power transformers operating together with cable lines or long busbars, which are caused by resonant overvoltages. Recently, there have been cases of failures of 110–750 kV generator step-up transformers, 10–110 kV distribution transformers, and wind turbine transformers for voltage levels up to 35 kV. In the first and second parts of the article, an attempt is made to develop the theory of resonant processes in power transformer windings. The results of theoretical studies of the frequency responses in a homogeneous chain circuit containing two and four PI section were presented, and conclusions about the voltage resonance occurrence conditions were drawn. The third part of the article presents the results of theoretical studies of transients in a homogeneous chain circuit containing two PI sections. Analytical expressions are obtained for the transient voltage under the impact of a step voltage impulse and a voltage impulse with an exponentially rising front. The influence of the impulse front duration on the free transient voltage component amplitude is analyzed. Analytical expressions for the transient voltage in the considered equivalent circuit under the influence of undamped and damped sinusoidal voltage are given. Expressions for estimating the maximum resonant voltage amplification ratio under the influence of a damped sinusoidal voltage are obtained.