A transformer is an electromagnetic device that transfers electrical energy between different
voltage levels. During this transfer, losses occur which cause heating and reduce overall
efficiency. Despite high efficiencies, manufacturers strive for further reduction and control of
losses. While ohmic and core losses are relatively well-defined, a higher degree of uncertainty
remains regarding losses in other transformer components, known as stray losses. Although
these typically represent a small fraction of total losses, their impact must not be neglected, as
they can cause local hot spots and consequently affect the transformer's operation.
The first part of the thesis involves a detailed analysis of a selected transformer type. The active
parts and key structural elements are addressed, including the magnetic core, windings, yoke
and limb clamps, magnetic shields, and the transformer tank. For each element, structural
parameters and specific material properties are defined, which are crucial for the development
of an accurate numerical model. Special emphasis is placed on the analysis of stray loss
generation within the structural components and windings.
Based on the findings from the initial model analysis, a simplified model was designed in the
second part of the work, intended for predicting transformer losses during the design phase.
Winding ohmic losses are calculated analytically based on transformer parameters, while losses
in the connections are estimated using a newly developed semi-empirical equation. Winding
eddy current losses are determined analytically based on the 3D magnetic field. Losses in other
conductive elements are determined using a 3D model that includes the main conductive
components: the tank, limb and yoke clamps, and magnetic shields. The results of the simplified
model were verified against measured values, based on which the most accurate method for
predicting load losses were determined.
The methodological section includes the definition of material properties, the generation of the
finite element mesh, and the setup of boundary conditions in the Ansys Maxwell 3D
environment. The electrical and magnetic characteristics of the components are derived from
the software library and material data sheets. Furthermore, the skin depth calculation for
capturing eddy currents, the configuration of the eddy current solver, and the winding excitation
method are presented. This model setup enables an accurate numerical evaluation of ohmic and
stray losses, providing a basis for model validation through comparison with load losses
measurements.
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