Towards short‐circuit proof design of power transformers

Abstract

Purpose -The purpose of this paper is to give a comprehensive description of various safety factors that need to be determined while assessing the short-circuit strength of transformers. Design/methodology/approach -Factors of safety are divided into two categories: radial and axial. Some of the latest approaches in assessing the strength are elaborated. Findings -Six major sets of calculations are identified: three each for radial and axial electromagnetic forces. Corresponding factors of safety are defined and calculated for practical transformers. These factors are related to the strength and stability aspects of windings.Research limitations/implications -The work gives pointers for further research at appropriate places while highlighting the challenges involved in the assessment of the short-circuit strength. Practical implications -The presented overview of the factors of safety can be a useful guide for the practicing transformer engineers. Originality/value -The main contribution of the reported work is in highlighting the intricacies associated with the subject of short-circuit strength of power transformers. It can serve as a reference document for future research works in the area since the procedures are outlined for calculating the factors of safety through six case studies.

Analyzing Short Circuit Forces in Transformer for Double Layer Helical LV Winding using FEM

“…It has been found that the forces computed by 3D and simplified 2D asymmetric FEM methods agree with each other: the total forces in front view and end view are quite close, and the forces in the window region are larger than the forces along the circumference of the winding [10]. Safety factors for radial and axial forces during short circuit in a power transformer have been proposed using the results of FEM [2]. FEM was for the first time applied to a helical winding to study the effect of transposing the windings [5].…”

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

“…In [3] Bertagnolli gives the overview of the short circuit causes, manufacturing experiences and criteria for improving the chances of passing the short circuit testing. 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).…”

“…When calculating the total radial force in the outer part of the winding, instead of N and B 0 , k N •N and k B •B 0 should be used in (5) and (6). According to Figure 4(b) which corresponds to the case of 1 cooling duct shown in Figure 3, when the radial force is calculated in the outer half of the LV winding only half of the turns are included and the mean flux density there is 3/4 of the flux density in the main cooling duct (B 0 ), therefore k N = 1/2 and k B = 3/4.…”

A Genetic Algorithm-Based Approach for Three-Phase Fault Evaluation in a Distribution Network

“…the root mean square value of maximum current and magnitude of the first peak [5]. These values are for use in power system designing [8,25].…”

“…Recent software tools e.g. ETAP (Electrical Transient Analysis Program), Easy-Power and Matlab [7,8].…”