Short-Circuit Strength of Power Transformer Windings-Verification of Tests by a Finite Element Analysis-Based Model

Abstract

A test stand to evaluate the radial buckling strength of power transformer windings under the influence of electromagnetic forces is presented. The resulting conductor deformation can be measured in parallel to the sinusoidal test current. The proposed test results focus on the inception of forced buckling for continuously transposed conductors (CTCs), which are a special type of conductors often used in power transformer windings. In literature, there barely exist calculations to the radial buckling withstand capability of CTCs. Therefore, a Finite Element Analysis (FEA) based simulation model for this kind of conductor is proposed and verified by the tests. For this verification, three different CTC types are used. The final simulation model is based on a coupled analysis of magnetostatic force calculation and static structural deformation analysis. It suitably reproduces the measurement results from the dynamic short-circuit tests. Furthermore, a standard formula describing radial buckling phenomena inside power transformers is adapted for the use with CTCs.Index Terms-Power transformer, short circuit forces, continuously transposed cable (CTC), forced buckling, Finite Element Analysis (FEA). 0885-8977 (c)

Mechanical Behaviour of the Cellulosic Dielectric Materials of Windings in Power Transformers in Operation

“…Another extension of this study that must be considered is to apply a cyclic load both in the simulation and in the laboratory, which would be a more realistic representation of a sinusoidal short-circuit current affecting the transformer windings. The deformation applied in the laboratory could be analogous to the one which is exemplified in [5].…”

“…Because there are previous references which analyse some aspects of the performance of a CTC from a mechanical point of view (such as [3], [4] or [5]) and there is also an interest from manufacturers on improving the understanding of the degradation processes which could lead to the end of life of transformers, we are focusing in extending those analyses. In particular, we will study a real commercial CTC conductor with its insulating paper, which can be seen in Fig.2.…”

Experimental and numerical analysis of cellulosic insulation failures of continuously transposed conductors under short circuits and thermal ageing in power transformers

“…As a very similar strain field will appear in the paper insulation in which the copper is wrapped, a failure model could be developed to predict the critical load state that leads to failure. This paper contributes to extending some previous analyses (such as [3][4][5][6][7]), to understand the mechanical response and degradation processes which could lead to the end of life of transformers. There are many studies analysing the mechanical behaviour of cellulosic materials, but only a few of them are specific for the insulation of transformers (such as [8][9][10][11][12]).…”

Critical stress of oval foil winding with epoxy coated insulation determined using measured equivalent modulus of elasticity

“…In [6] factors of safety for the radial and axial forces, effects of temperature, moisture and aging and ways of improving short circuit withstand capability are described. Bakshi and Kulkarni [7] give buckling strength analysis of inner windings of power transformers under radial short-circuit forces, while Geissler [8] presents the finite element analysis of radial buckling strength with the focus on continuously transposed conductors (CTCs).…”