Original scientific paper
COUPLED MAGNETO-MECHANICAL FINITE ELEMENT ANALYSIS OF A POWER TRANSFORMER IN SHORT CIRCUIT CONDITIONS
Bruno Bošnjak
orcid.org/0000-0001-9432-8223
; Siemens AG Power Transformers Nürnberg
Andreas Hauck
; SIMetris GmbH
Hermann Landes
; SIMetris GmbH
Abstract
External short circuit is one of the most demanding load conditions a transformer can be
subjected to. Short circuit withstand capability of power transformers is therefore quintessentially
important in order to ensure the proper functioning of a power transformer during its lifetime. Accurate
calculation of the forces and stresses a transformer is subjected to during a short circuit is a prerequisite
for better, optimized design of the active part. Main focus of this paper is the investigation into dynamic
electromagnetic and mechanical behaviour of a transformer winding subject to an external short circuit.
For purposes of this simulation, a single-phase 100 MVA autotransformer active part was modelled using
ANSYS and NACS software. Particular areas of the winding were modelled to a greater degree of detail
in order to observe the effects of Lorentz forces during a short circuit on individual conductors. A transient
coupled magneto-mechanical simulation of the transformer under short circuit conditions was carried out.
When subject to dynamic short circuit forces, the winding discs exhibited a profoundly resonant
behaviour indicating a strong relationship between the natural frequency of the winding and the resulting
stresses and displacements incurred during a short circuit. It has been shown that the position of the yoke
changes the orientation and the distribution of the magnetic field vectors at the top and the bottom of the
winding, causing a non-uniform distribution of forces along the top discs of the winding. This non-uniform
distribution of forces along the circular shape of the winding conductor caused high stresses at the
positions within the winding which were previously considered to be under lower stress when calculated
using 3D static FEM and analytical methods.
Keywords
Transformer; Short Circuit; Lorentz Forces; Stress; Multiphysics; Transient; FEM
Hrčak ID:
199247
URI
Publication date:
15.8.2017.
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