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Terminal models of transformers for transient studiesAcosta Aradillas, Juan January 1984 (has links)
No description available.
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High Temperature Superconducting Partial Core TransformersLapthorn, Andrew Craig January 2012 (has links)
The thesis begins by providing an introduction to transformer theory. An ideal transformer is examined first, followed by full core transformer theory. The partial core transformer is then introduced and compared to the full core design. An introduction to superconductors is then presented where a simplified theory of superconductivity is given. High temperature superconductors are then examined including their physical structure, superconducting properties and the design of the superconducting wire.
The early development of high temperature superconducting partial core transformers at the University of Canterbury is then examined. Early partial core development is discussed followed by some material testing at cryogenic temperatures. This work lead into the development of the first high temperature superconducting partial core transformer. This transformer failed during testing and an examination of the failure mechanisms is presented. The results of the failure investigation prompted an alternative winding insulation design which was implemented in a full core superconducting transformer.
The modelling used to design a high temperature superconducting partial core transformer is then presented. Based upon the reverse design method, the modelling is used to determine the components of the Steinmetz equivalent transformer circuit. The modelling includes a combination of circuit theory and finite element analysis. An ac loss model for high temperature superconductors is also presented.
A new 15 kVA, 230-230V high temperature superconducting partial core transformer was designed, built and tested. The windings are layer wound with first generation Bi2223 high temperature superconductor. The modelling was used to predict the performance of the transformer as well as the ac losses of the high temperature superconductor. A series of electrical tests were performed on the transformer including open circuit, short circuit, resistive load, overload, ac withstand voltage and fault ride through tests. The test results are compared with the model. The transformer was found to be 98.2% efficient at rated power with 2.86% voltage regulation.
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Development of a finite element matrix (fem)three-phase three-limb transformer model for Geomagnetically Induced Currents (GIC) experimentsMkhonta, Sizwe 10 February 2021 (has links)
Geomagnetically Induced Currents (GIC) have been a growing concern within power system operators and researchers as they have been widely reported to lead to power system related issues and material damage to system components like power transformers. In power transformers, GIC impacts are evidenced by part-wave saturation, resulting in transformers experiencing increased presence of odd and even harmonics. The three-phase three-limb (3p3L) transformer has been found to be the most tolerant to high dc values compared to other core types. The research was based on a hypothesis which reads “transformer laboratory testing results can be used as a guide towards developing suitable Finite Element Matrix (FEM) models to be used for conducting GIC/DC experiments”. This study thus investigates the response of a 15 kVA 3p3L laboratory transformer to dc current, emulating the effects of GICs. GIC and dc current are the same under steady state conditions, and hence mentioned interchangeably. Laboratory tests conducted identified two critical saturation points when the transformer is exposed to dc. The early saturation point was identified to be at around 1.8 A/phase of dc (18% of rated current), while the deep saturation point was at around 15 to 20 A/phase of dc (about 72% of rated current). Further analysis showed that holes drilled on the transformer can lower the transformer knee-point by about 26%, depending on the size and location of the holes. The holes hence end up affecting the operating point of the transformer due to losses occurring around the holes. A transformer FEM model was developed following the laboratory exercise, where it was concluded that a 2D model leads to grossly erroneous results, distorting the magnetizing current by about 60% compared to the laboratory results. A solid 3D model improved performance by about 30% as it took the transformer's topological structure into consideration. The 3D model was then refined further to include joints and laminations. It was discovered that laminations on the transformer need to be introduced as stacks of the core, with each core step split into two, allocating a 4% air gap space between stacks. Refinement of the T-joints proved that the joints have a relatively high influence on the transformer behaviour, with their detailed refinement improving the transformer behaviour by about 60%. The final FEM model was used for dc experiments. The results of such experiments showed close resemblance to the laboratory results, with saturation points identified in FEM lying within 10% of the laboratory identified saturation points. Overall, the various investigation methods explored showed that the hypothesis was satisfactorily proven true. Laboratory results functioned as a guide in developing the model, offering a reference case.
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Wide-band modelling of an air-core power transformer windingVan Jaarsveld, Barend Jacobus 12 1900 (has links)
Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The objective of this project is to develop an electromagnetic model that can be used to
accurately calculate the voltage distribution in a transformer winding structure when excited
with standard impulse excitation waves. This voltage distribution is required during the
design stage of a power transformer to ensure that the insulation is capable of withstanding
the occurring electric field stresses during these tests. This study focuses on the modelling
of a single disk-type power transformer winding without the presence of an iron-core.
Methods of calculating self- and mutual-inductances of transformer windings are presented
and validated by means of finite element method software simulations. The same is done for
the calculation methods used for calculating the capacitances in and around the winding
structure. The calculated and FEM-simulated results are compared to measured values as a
final stage of validation. The methods used to calculate the various model parameters seem
to produce results that agrees well with measured values. The non-linear frequency
dependant dissipative nature of transformer windings is also investigated and a methodology
to take this into account is proposed and implemented. The complete modelling
methodology proposed in this thesis, which includes the calculation of the model
parameters, model synthesis and solver algorithm, are applied to an actual case study. The
case study is performed on an air-core reactor manufactured using a disk-type power
transformer winding. The reactor is excited with standard lightning impulse waves and the
voltages along the winding are measured. The calculated and measured voltage wave
forms are compared in both the frequency and time-domain. From the comparison it is
found that the model accurately represents the actual transient voltage response of the testunit
for the frequency range of interest during standard factory acceptance tests. / AFRIKAANSE OPSOMMING: Die doel van hierdie projek is om 'n elektromagnetiese model te ontwikkel wat gebruik kan
word om die spanningsverspreiding in 'n transformatorwindingstruktuur te bereken as
standaard weerligimpulstoetse toegedien word. Hierdie spanningsverspreiding word vereis
tydens die ontwerpstadium van ‘n kragtransformator om te verseker dat die isolasie in staat
is om die elektriese veldsterkte tydens hierdie toetse te weerstaan. Hierdie studie fokus op
die modelering van 'n enkele skyftipe-kragtransformatorwinding sonder die teenwoordigheid
van 'n ysterkern. Metodes van berekening van self- n wedersydse-induktansie van
transformatorwindings word aangebied en getoets deur middel van Eindige-Element-Metode
(EEM) simulasies. Dieselfde word gedoen vir die metodes wat gebruik word vir die
berekening van die kapasitansies in en rondom die windingstruktuur. Die berekende en
EEM-gesimuleerde resultate word vergelyk met die gemeete waardes as 'n finale vlak van
bekragtiging. Die metodes wat gebruik word om die verskillende modelparameters te
bereken vergelyk goed met gemete waardes. Die nie-lineêre frekwensie-afhanklike verliese
van transformatorwindings word ook ondersoek en 'n metode om hierdie in ag te neem is
voorgestel en geïmplementeer. Die volledige voorgestelde modeleringsmetodiek in hierdie
tesis, wat die berekening van die modelparameters, modelsintese en oplosingsalgoritme
insluit word toegepas op 'n werklike gevallestudie. Die gevallestudie is uitgevoer op 'n
lugkern-reaktor wat 'n skyftipe-kragtransformatorwinding. Die reaktor word onderwerp aan
die standaard weerligimpuls golwe en die spanning al langs die winding word gemeet. Die
berekende en gemete spanning golf vorms word met mekaar vergelyk in beide die
frekwensie- en tyd-vlak. Uit die vergelyking blyk dit dat die model die werklike
oorgangspanningsweergawe van die toetseenheid akkuraat verteenwoordig vir die
frekwensie reeks van belang tydens standaard fabriekaanvaardingstoetse.
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