چكيده به لاتين
Given the unique electrical and magnetic properties of superconductors, in recent years,
researchers have begun to use these materials in the electrical industries. Although the
transformer is an important part of the power system, unfortunately due to the very large
magnetic losses caused by the high magnetic field applied to the superconducting wire, it is
the worst equipment in terms of ac losses. Nowadays, the application of non-linear loads gives
rise to a vastly increased level of harmonics in the power network. As such, the transport
currents of transformers are non-sinusoidal alternating currents.
The purpose of this thesis is to analyze the AC losses of three-phase superconducting
transformer in the presence of harmonic currents. The computation of AC losses by traditional
techniques, is suitable for the sinusoidal current condition. So, in the first step, two accurate
analytical methods are proposed to these losses estimation in three-phase superconducting
transformer considering harmonic loads for the first time and the results of these proposed
methods are compared with a FEM-based numerical method. The results prove the accuracy,
speed of calculation, yet efficiency of the proposed methods. Next, the AC losses in threephase superconducting distribution transformer for multi-harmonic spectra and independent
harmonics are analyzed in detail. According to the results, harmonics change the number of
peaks and amplitudes of the current waveform passing through the windings, so that in
addition to the major hysteresis loop, a number of minor hysteresis loops are also formed.
Therefore, the harmonic current changes the rate of AC loss, which is completely hysterical in
nature. AC losses increase for most harmonic spectra. However, the simulation results reveal
that due to the harmonic compensation effect, for some harmonic distortion coefficients, AC
losses are reduced. The behavior of these losses depends on three basic parameters of the
harmonic current waveform, namely: amplitude, phase angle, and order of harmonic content.
For a particular harmonic order, the impact of the phase angle on the losses changes decreases
with increasing amplitude of the harmonic component. In a specified harmonic amplitude, as
the harmonic order increases, the effect of the phase angle on the losses diminishes. Due to
the significant impact of increasing losses on equipment and cooling costs, the overall
efficiency and economic feasibility of the transformer, in the following, three new solutions
based on making changes in the windings structure to reduce harmonic losses are proposed.
The results of simulations and calculations show the significant usefulness of the mentioned
structures on reducing leakage flux and harmonic losses. Since the slope of the increment in
losses will significantly augment as the harmonic order increases, in the next step, the
sensitivity of AC losses to high-order harmonic components of the transport currents with
different harmonic factors and total harmonic distortions, is analysed. It is observed that in the
presence of these loads, the hybrid winding structure is the best in terms of reducing harmonic
AC losses. The transformer simulations are performed using finite element software FLUX
2D/3D. MATLAB and Maple softwares are used in parallel to perform analytical methods.
