The objective of this thesis is to develop a simplified high-frequency model for
three-phase, two- and three-winding transformers. The model is an extension of the
classical 60 Hz model which includes two important factors prevailing in transformers
under transient conditions: stray capacitances which cause transformers to resonate and
frequency dependent characteristics of the leakage flux and winding resistances due to
skin effects. The model is not aimed to represent internal details of the transformer and
only lumped circuit parameters are used in order to simulate terminal behaviours of the
transformer. However, it is different from other terminal models in that it is not just an
impedance or admittance black box derived from measured transfer functions. Only the
meaningful parameters which correspond to the physical components in the real transformer
are included in the model.
The short-circuit impedances T-form of the classical model is retained which
makes it possible to separate the frequency-dependent series branch form the constantvalued
capacitances. In addition, it enables the model to be built at the coil level which is
independent of winding connections. The model stray capacitances are placed at the
corresponding coils terminals. If they link two coils they will be split into two halves with
one half connected at the upper ends and the other half at the lower ends. The frequency dependent series branch is divided into sections corresponding to various sections in the
transformer coil which can be assumed uniform. An RL equivalent network is used to
synthesise the frequency dependent behaviour of each section. The values of R's and L's
are calculated from minimum-phase-shift approximations which guarantees numerical stability
of the resulting network. With the use of symmetrical components, mathematical
complications of fitting mutual impedance functions are avoided and also the number of
impedance functions to be fitted by rational functions is reduced.
A number of short-circuit tests on the actual power transformers installed in the
Thailand 's power system were performed to determine the parameters of the model. The
frequency responses calculated from the model are compared with the tests. Also, a timedomain
test was conducted and the result was used for comparison with the simulation
from the model.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:BVAU.2429/8775 |
| Date | 05 1900 |
| Creators | Chimklai, Suthep |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Relation | UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/] |
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