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This thesis aims to design transformer-based balanced passive components with high performance and compact size using CMOS and printed-circuit¡Vboard (PCB) technologies. A CMOS parallel-combining transformer (PCT) incorporating a planar trifilar transformer is presented to realize power combining and impedance transformation at the same time. In addition, a CMOS Wilkinson power combiner with a planar bifilar transformer is proposed to enhance isolation between two combining ports. Several transformer coupled balun designs with an overlay winding structure are carried out on FR4 and Duroid substrates. These designs uses a rather symmetric layout to achieve a superior balance performance and a multilayer configuration to create the transmission zeros in the out-of-band response. Finally, a CMOS transformer balun is implemented with a bandpass filter passband which is designed according to the coupled resonator filter theory. This passband can restrict the bandwidth usage for the balun to improve the common-mode rejection ratio (CMRR) within the passband.

No description available.

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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.

In electrical power distribution and power electronic applications, a transformer is an indispensable component which performs many functions. At its operating frequency (60/50 Hz), it is one of the most bulky and expensive components. The concept of the electronic transformer introduced previously has shown considerable reduction in size, weight, and volume by operating at a higher frequency. In this dissertation, the concept of the electronic transformer is further extended to the auto-connected phase-shifting type to reduce harmonics generated by nonlinear loads. It is shown that with the addition of primary side and secondary side AC/AC converters achieves phase-shifting. With the addition of converters, magnetic components are operated at a higher frequency to yield a smaller size and weight. Two types of auto-connected electronic transformer configurations are explored. In the first configuration, the secondary converter is eliminated and the output is suitable for rectifier type loads such as adjustable speed drives. In the second configuration, the secondary converter is added to obtain a sinusoidal phase-shifted AC output voltage. This approach is applicable in general applications. With the proposed approaches, the th and 7th harmonic in utility line currents, generated by two sets of nonlinear loads, are subtracted within the electronic transformer, thereby reducing the total harmonic distortion (THD) of the line current. The analysis and simulation results are presented. In the second part of the dissertation, the electronic transformer concept is applied to a telecommunication power supply (-48 VDC) system. The proposed approach consists of a matrix converter to convert the low frequency three-phase input AC utility to a high frequency AC output without a DC-link. The output of the matrix converter is then processed via a high frequency isolation transformer to produce -48 VDC. Digital control of the system ensures that the output voltage is regulated and the input currents are of high quality, devoid of low frequency harmonics and at near unity input power factor under varying load conditions. Due to the absence of DC-link electrolytic capacitors, the power density of the proposed rectifier is shown to be higher. Analysis, design example and experimental results are presented from a three-phase 208 V, 1.5 kW laboratory prototype converter.

Streamer characteristics, breakdown strengths and gassing behaviour of insulating liquids under electric stresses are taken into account for a reliable design and safe operation of the transformer. Ester liquids which are biodegradable and have high fire point have been widely used in distribution transformers and some power transformers in recent years. It is also interesting to introduce ester liquids into High Voltage Direct Current (HVDC) converter transformers due to the fast development of HVDC transmission lines. Therefore, this thesis aims to investigate the pre-breakdown, breakdown characteristics and gassing behaviour of a synthetic ester liquid under DC and various impulse voltages where a mineral oil is tested as the benchmark. A comprehensive study of streamer characteristics and breakdown strength of the mineral oil and the synthetic ester liquid under both positive and negative DC voltages was carried out in the point-plane electric fields. Characteristics of streamer length, propagation velocity and shape were analysed based on shadowgraph images obtained at a gap distance of 10 mm, using a multi-channel ultra-high speed camera. Streamer inception voltages with the tip radii of 5 µm, 10 µm, 20 µm and 50 µm and breakdown voltages at various gaps of 2 mm, 5 mm, 10 mm, 20 mm and 30 mm were also investigated. The results indicate that there is no obvious streamer propagation (less than about 10% of the gap distance) under negative polarity even when the applied voltage approaches breakdown voltage. At the same applied voltage level, the streamer in the synthetic ester liquid propagates faster and further than that in the mineral oil. As a result, the breakdown voltages of the synthetic ester liquid are lower than those of the mineral oil at all the gap distances investigated under both polarities. Experimental and modelling studies of pre-breakdown and breakdown phenomena in the mineral oil and the synthetic ester liquid under impulse waveforms with different tail-time were carried out in the point-plane electric fields. A compact solid-state switch based impulse generator was used to provide different impulse waveforms from short tail-time to 'step-like' tail-time: 0.8/8 µs, 0.8/14 µs, 0.8/30 µs and 0.8/3200 µs. A point-plane electrode configuration with a small gap distance of 10 mm and a tip radius of 10 µm was used. The results indicate that the shorter tail-time impulse waveform results in a shorter stopping length and higher breakdown voltage; however it does not affect the instantaneous breakdown voltage and time to breakdown. A mathematical model is therefore described to predict the breakdown voltage under different impulse waveforms. In addition, with the similar stopping length, higher energy injected from the short tail-time impulse caused the streamers to have more branches than those under the long tail-time impulse. The characteristics of fault gas generation in the mineral oil and the synthetic ester liquid under various levels of electrical faults were studied. A test platform with functions of automatic spark fault control and data acquisition was developed. The effects of spark numbers (from 20 to 500), gap distance (5 mm and 10 mm) and voltage levels (Vb-99.9% and 1.5Vb-99.9%) on fault gas generation in liquids were studied. The key gases in the mineral oil are H2 and C2H2, while the key gases in the synthetic ester liquid are H2, C2H2 and CO. The amount of fault gas generation increases linearly with the number of sparks. However, the number of sparks does not have an obvious effect on fault gas pattern and gas generation per unit fault energy in µL/J. Spark at a larger gap distance or under a higher applied breakdown voltage generates more fault gases due to higher injected fault energy.

In recent years, the trade-off between quality and cost of power system components has become a matter of interest for many utilities. The widespread use of costly electricity networks either in residential or industrial areas has encouraged service providers to find a proper strategy that will minimize the overall life-cycle cost while keeping components in good working condition. The power transformer, which represents approximately 60% of the overall cost of the network, is ranked as one of the most important and expensive components. However, the transformer's sudden failure puts the system in a serious or critical condition which in most cases causes catastrophic loss to both utilities and customers. Significant attention has been given to monitoring and diagnostic techniques that observe any abnormal behaviour, assess the transformer's condition, and therefore minimize the probability of unplanned outage. Yet, applying many various monitoring tests is not always applicable due to the following factors: some tests require the unit to be taken out from service for testing, insufficient availability of man power, and significant cost of applying all the tests. Thus, there is a vital demand for an intelligent method of minimizing the number of monitoring tests without losing much information about the transformer's actual condition. In this research, data mining techniques have been employed to evaluate the transformer's state through intelligent selection criteria that determines the optimal number of monitoring tests in cost-effectiveness. Feature selection technique based on ranker search method has been used to rank the monitoring tests (features) in a priority sequence from their individual evaluation, and to select the most inductive tests that provide the most information about the unit's condition. When the measured data from monitoring tests is collected and prepared, a diagnostic technique is applied to assess the condition of the transformer. In this regard, Support Vector Machine (SVM) has been utilized to perform this task due to its robust classification accuracy. SVM is first applied to the full number of tests, and then the number of monitoring tests is reduced by one after each classification process using the feature selection algorithm. The selected number of monitoring tests has shown the best possible accuracy the classifier can reach over the whole number of tests. Radial Basis Function (RBF) classifier has been used in the classification process for results comparison purposes. This proposed work contributes towards finding an intelligent method of evaluating the transformer state as well as minimizing the number of tests without losing much information about the unit's actual condition. Therefore, this method facilitates deciding a wise course of action regarding the transformer: either maintain, repair, or replace.