عنوان

Generation and propagation of harmonics in power system feeders containing nonlinear transformers and loads

TLpq303932577

انگلیسی

Generation and propagation of harmonics in power system feeders containing nonlinear transformers and loads

[Thesis]

M. A. Sherkat Masoum

E. F. Fuchs

University of Colorado at Boulder

1991

329

Ph.D.

University of Colorado at Boulder

1991

The problem of modifying the harmonic power flow analysis to permit the inclusion of nonlinear anisotropic transformers, so far neglected in power flow studies, constitutes the objective of this thesis. A new approach for the determination of usd\lambdaiusd characteristics of anisotropic transformers is presented using a quasi three-dimensional nonlinear magnetic field analysis. Saturation of iron-core, anisotropy of laminations, presence of interlamination and butt-to-butt air gaps are properly modeled using computed representative usdB\sb{m}H\sb{m}usd and loss-density characteristics for the yokes and the legs of transformers. The computed usd\lambdaiusd and representative loss-density characteristics are used with the so-called phase-factor functions to develop a large-signal non-linear model of anisotropic transformers for (non)sinusoidal operating conditions and (non)linear loads. The newly defined phase-factor functions reflect the increase or decrease in the iron-core losses caused by the presence of harmonics of the terminal voltage. The percentage increases of losses with respect to rated losses and the derating of transformers are computed for different nonsinusoidal terminal voltage waveshapes: it is shown that for some nonsinusoidal waveforms the iron-core losses could be less than the iron-core losses at sinusoidal terminal voltage and rated output conditions. Computed and measured flux linkage functions and (copper and iron-core) losses show good agreement for a 1kVA single-phase transformer. Finally, the large-signal nonlinear model of transformers is used to develop a harmonic load flow algorithm capable of simulating nonlinear transformers situated within power systems and to compute their iron-core and copper losses by modifying an existing harmonic load flow algorithm. The convergence properties are similar to the harmonic load flow algorithm with linear transformers. A simple example consisting of a linear load, a full-wave bridge rectifier and an anisotropic transformer with linear loads is examined. Computed and measured losses of a single-phase circuit consisting of a linear load and a 1 kVA anisotropic transformer show good agreements. The main contributions of this thesis are: (1) A large-signal nonlinear model of anisotropic transformers for nonsinusoidal operations. (2) A harmonic load flow algorithm capable of simulating nonlinear transformers. (3) A methodology which is general enough that it can be applied to other anisotropic transformers (e.g., large distribution transformers) in computing their losses or optimizing their designs.

Applied sciences

Electrical engineering

Engineering

transformers

E. F. Fuchs

M. A. Sherkat Masoum

p

[Thesis]

276903

a

Y