Influence of oil temperature on frequency characteristics of disk and layer transformer windings

Abstract

Transformers operating in the power grid or in an industrial environment may be subjected to transients or stimulus with different wave fronts. In industrial networks distribution transformers are exposed to many switching operations which often generate overvoltages. Overvoltages usually have oscillatory components. These components can be sources of resonance inside overvoltages in transformers. If the spectrum of incoming surge voltage matches that of the winding, a corresponding winding resonance will be excited. Therefore external transients occurring in power systems can trigger internal overvoltages with large maximum values in the transformer windings. An analysis of the influence of oil temperature on the frequency characteristics of voltage in transformer windings is very important from a practical point of view. The impact of oil and temperature on the frequency characteristics of internal voltages are presented in this paper. Time domain step response signals of transient voltages in windings, generated for a given step voltage with a selected rise time, are also presented. The paper presents investigation results for disc and layer model transformer windings. The presented results might be used both in the design and optimization of transformers windings.