The Study of Two Models for Power Transformer Winding Deformation

Transformer, one of the most important components in a power system, functions as the vital to the safety of power supply system. However, great economic losses and industrial accidents can result from transformer winding deformation. Therefore, it is quite essential to use a precise transformer model when taking simulation to diagnose the transformer winding deformation correctly and instantly. And many studies show that there are two models of transformer winding used mostly and performing well in the simulation of transformers with the fault. One is equivalent circuit model, and the other is multi-conductor transmission line model. To tell the difference of these two models, we performed the study on power transformer SFSZ11-180000/220 and SF11-31500/35 and got the frequency response curves from the equivalent circuit models using inter-turn and inter-disc parameters and multiconductor transmission line model. And the conclusions are that both equivalent circuit model and multi-conductor transmission line model can reflect the degree of bulge deformation. However, multi-conductor transmission line model can reflect the degree of bulge deformation in wider frequency range. In addition, it will cause the difference of frequency curves whether the parameters used in models are inter-turn or inter-disc for equivalent circuit model multi-conductor transmission line model.

I. Introduction

Among transformer winding deformation detection methods, frequency response analysis (FRA) method is one of the most widely used methods at present [1]–[2]. The basic principle of this method is that the deformation or displacement of the winding will cause its impedance to change, which will change the characteristics of the FRA curve [3]–[4]. FRA measurement has been standardized, and many studies focus on the interpretation of FRA measurement results now [5]. To get frequency response curves, a precise transformer model used for modeling is quite essential. Many studies show that there are two models of transformer wingding used mostly and performing well in the simulation of transformers with the fault. One is equivalent circuit model, which can either model all parts of the transformer in details or be constructed according to gross physical components such as the winding layers [6]–[7]. This type of model uses network equivalent parameters (resistances, inductances and capacitances) and focus on the frequency range of interest. And the other is multi-conductor transmission line model, which provides the terminal characteristics of a transformer and is not necessarily related to a transformer internal condition and physical configuration [8]–[9]. This type of model mainly describes the terminal characteristics, and can be constructed by mathematical equations. From the principle of two models, in addition to the difference of basic principle, the electrical circuit parameters of multi-conductor model line adopt the interturn data while that of equivalent circuit model use the inter-disc data. To tell if it is this reason that causes the difference of the frequency response curve, we established the equivalent circuit model using interturn data and inter-disc data respectively. And we performed the study on power transformer SFSZ11-180000/220 and SF11-31500/35 and got the frequency response curves from the models using inter-turn and inter-disc parameters, and draw the conclusion that both equivalent circuit model and multi-conductor transmission line model can reflect the degree of bulge deformation. However, multi-conductor transmission line model can reflect the degree of bulge deformation in wider frequency range. In addition, it will cause the difference of frequency curves whether the parameters used in models are inter-turn or inter-disc for equivalent circuit model multiconductor transmission line model.