Wideband modelling and parameter estimation of two-winding transformers

Brozio, C. C. (1999-12)

Thesis (PhD)--University of Stellenbosch, 1999.

Thesis

ENGLISH ABSTRACT: This dissertation proposes a new wideband, lumped-parameter equivalent-circuit transformer model that is suitable for parameter estimation applications, while reflecting the internal electromagnetic behaviour of the transformer in its structure. Frequency-dependence of the resistive and inductive model elements is investigated experimentally and provision is made for these effects in the model structure. A procedure by which the parameters of the proposed model structure can be estimated directly from terminal frequency response measurements is developed and applied to a 16 k VA, 22 kV / 220 V single-phase distri bution transformer and a 11kV/110 V single-phase voltage transformer. The transformer model is validated by applying it to frequency-domain and time- domain simulations in the frequency range between 10 Hz and 100 kHz. The results show that the proposed model is able to accurately predict transformer responses in this frequency range, including all prominent winding resonances. The physical significance of the model structure is validated by comparing the frequency response of the voltage induced in a search coil around the core of the 11 kV / 110 V voltage transformer to the magnetizing branch voltage predicted by the model. From this comparison it could be concluded that the proposed transformer model correctly represents the magnetic coupling between the transformer windings. Keywords: Transformer, Wideband modelling, Parameter estimation

AFRIKAANSE OPSOMMING: In hierdie proefskrif word 'n nuwe wyeband, saamgevoegde-parameter, ekwivalente stroombaan transformator-modelstruktuur voorgestel. Hierdie modelstruktuur is geskik vir die toepassing van parameter afskattingsmetodes en weerspieel die interne elektromagnetiese gedrag van die transformator. Frekwensieafhanklikheid van die resistiewe en induktiewe modelelemente word eksperimenteel ondersoek en voorsiening vir hierdie effekte word in die modelstruktuur gemaak. 'n Metodiek waardeur die parameters van die voorgestelde model vanaf terminaal frekwensieweergawe-metings afgeskat kan word, is ontwikkel en word toegepas op 'n 16 kVA, 22 kV/ 220 V enkelfase distribusietransformator en 'n 11 kV / 110 V enkelfase spanningstransformator. · Die geldigheid van die transformatormodel word bevestig deur dit in die frekwensiebereik tussen 10 Hz en 100 kHz toe te pas, in frekwensiegebied- en tydgebied-simulasies. Die resultate toon dat die voorgestelde model akkurate voorspellings van transformatorweergawes in hierdie frekwensiebereik lewer, insluitende alle prominente windingsresonansies. Die geldigheid van ·die modelstruktuur, ten opsigte van ·die interne elektromagnetiese gedrag van die transformator, is ondersoek deur die frekwensieweergawe van die spanning wat in 'n soekspoel om die kern van die 11kV/110 V spanningstransformator ge1nduseer word, te vergelyk met die magnetiserings-takspanning wat deur di~.model voorspel word. Hieruit kon die gevolgtrekking bereik word dat die voorgestelde transformator modelstruktuur die magnetiese koppeling tussen die transformatorwindings korrek verteenwoordig. Sleutelwoorde: 'fransformator, Wyeband modellering, Parameter afskatting 111

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