Eigenvalue Analysis for Investigation of Tilting of Transformer Winding Conductors Under Axial Short-Circuit Forces

Abstract

The tilting phenomenon may lead to a catastrophic failure, such as an interturn fault in transformers, under the action of axial short-circuit electromagnetic forces. In this paper, first, a state-space approach has been used to determine the eigenvalues of various winding configurations used in practice by assuming a small value of tilt angle up to 10 . These eigenvalues decide the critical tilting forces and the natural frequencies of windings. The four cases involving disk, layer, helical windings (all these with strip conductor), and layer winding with continuously transposed cable conductor have been analyzed. Further, initial critical tilt angles are determined for various magnitudes of the axial force in a typical 5-MVA transformer.

An Investigation of Winding Curvature Effect on the Mechanical Strength of Transformer Windings

“…By using equation (2) the value of the strains y ε and z ε is 0.43 × 10 ̶ 3 . The corresponding stress value for both y σ and z σ is 51.4 MPa obtained by using (4).…”

“…5. Compute the resultant stress distribution corresponding to the resultant strain along the radial thickness by using the relation given in (4). Also compute the stresses y σ and z σ corresponding to the strains y ε and z ε as computed in step-1.…”

“…On the inner winding, the direction of radial force is towards the core and on the outer winding it is away from the core. The failure mechanisms of the windings due to the axial force are tilting of the conductors, axial bending between the radial insulation spacers, damage to the clamping rings, and torn conductor insulation [1][2][3][4][5]. For balanced ampere-turns and approximately equal heights of the windings, the directions of axial forces on the windings, are towards their centers from both the sides.…”

Towards short‐circuit proof design of power transformers

“…In order to determine the initial critical tilt angle in the disk coils, the assumption of a small tilt angle does not work (Bakshi and Kulkarni, 2011). The state-space equations for this system are given as:…”

Determination of Transformer Winding Radial Deformation Using UWB System and Hyperboloid Method

“…In industrial plants, mechanical damages such as radial deformations are caused by forces due to high short circuit currents [2]- [5]. The proper design, monitoring and investigation of the forces acting on the transformers are crucial [6], [7]. There are many transformer monitoring methods such as short circuit test method, frequency response analysis method and low voltage impulse test method [8]- [10].…”