The thesis begins with an introduction to transformer theory. The partial core transformer is then introduced and compared with a full core design. A brief introduction to superconductors and high temperature superconductors is then presented. High temperature superconducting fault current limiters are then examined and the advantage of a high temperature superconducting partial core transformer and fault current limiter as a single unit is highlighted. The reverse design model is discussed followed by the model parameters that are used in designing the high temperature superconducting partial core transformer. Partial core transformers with copper windings and high temperature superconductor windings at the University of Canterbury were then tested and the measured results compared with the results calculated from the reverse design model, to validate the model. The high temperature superconducting partial core transformer failed during an endurance run and the investigation of the failure is then presented. The results of the failure investigation prompted an alternative winding insulation design. A model to calculate the time at which the high temperature superconducting winding of the partial core transformer would melt at different currents was then built. The time was calculated to be used in the operation of the quench detection mechanism and it could also be used in choosing a circuit breaker with a known operating time. The design of the high temperature superconducting partial core transformer and fault current limiter is then presented. Design configurations with different core length and winding length are examined. The idea behind choosing the final design for the high temperature superconducting partial core transformer and fault current limiter is then discussed. The final design of the high temperature superconducting partial core transformer and fault current limiter is then presented. A new 7.5 kVA, 230-248 V high temperature superconducting partial core transformer and fault current limiter was designed, built and tested. The windings are layer wound with first generation Bi2223 high temperature superconductor. A series of electrical tests were performed on the new device including open circuit, short circuit, resistive load, overload and fault ride through. These tests were performed to determine the operational characteristics of the new high temperature superconducting partial core transformer and fault current limiter. The measured results from the tests were compared with the calculated results. The fault ride through test results were then compared to a 15 kVA high temperature superconducting partial core transformer that was designed and built at the University of Canterbury. Since the resistive component of the silver matrix in Bi2223 high temperature superconductor plays a very little role in controlling the fault current, the current limited by the leakage reactance is compared between the two devices. The high temperature superconducting partial core transformer and fault current limiter was found to be 99.1% efficient at rated power with 5.7% regulation and fault current limiting ability of 500 % over the 15 kVA high temperature superconductor partial core transformer from University of Canterbury.

No description available.

Superconductivity Centennial Conference 2011- EUCAS–ISEC–ICMC (18-23 Sep 2011, The Hague, The Netherlands)

Electrical power systems play a key role in production and services in both the industrial and commercial sectors and significantly affect the private lives of citizens. A major asset of any power delivery system is the transformer. Transformers represent extensive investment in any power delivery system, and because of the notable effect of a transformer outage on system reliability, careful management of this type of asset is critical. In North America, a large proportion of transformers is approaching the end of their life and should be replaced. In many cases, unexpected transformer outages can be catastrophic and cause both direct and indirect costs to be incurred by industrial, commercial, and residential sectors. Direct costs include but are not limited to loss of production, idle facilities and labour, damaged or spoiled product, and damage to equipment. For commercial customers, the effects may include damage to electrical and electronic equipment, and in some cases damage to goods. For residential customers, outages may cause food spoilage or damage to electrical equipment. In addition to direct costs, there are several types of indirect costs may also result, such as accidental injuries, looting, vandalism, legal costs, and increases in insurance rates. The main goal of this research was to assess the health and remaining lifetime of a working transformer. This information plays a very important role in the planning strategies of power delivery systems and in the avoidance of the potentially appalling effects of unexpected transformer outages. This thesis presents two different methods of assessing transformer end of life and three distinct methods of determining the health index and health condition of any working transformer. The first method of assessing transformer end of life is based on the use of Monte Carlo technique to simulate the thermal life of the solid insulation in a transformer, the failure of which is the main reason for transformer breakdown. The method developed uses the monthly average ambient temperature and the monthly solar clearness index along with their associated uncertainties in order to estimate the hourly ambient temperature. The average daily load curve and the associated uncertainties in each hourly load are then used to model the transformer load. The inherent uncertainties in the transformer loading and the ambient temperature are used to generate an artificial history of the life of the transformer, which becomes the basis for appraising its remaining lifetime. The second method of assessing transformer end of life is essentially an economic evaluation of the remaining time to the replacement of the transformer, taking into consideration its technical aspects. This method relies on the fact that a transformer fails more frequently during the wear-out period, thus incurring additional maintenance and repair costs. As well, frequent failures increase during this period also costs related to transformer interruptions. Replacing a transformer before it is physically damaged is therefore a wise decision. The bathtub failure model is used to represent the technical aspects of the transformer for the purposes of making the replacement decision. The uncertainties related to the time-to-failure, time-to-repair, time-to-switch, and scheduled maintenance time are modeled using a Monte Carlo simulation technique, which enables the calculation of the repair costs and the cost of interruptions. The repair, operation, and interruption costs are then used to generate equivalent uniform annual costs (EUACs) for the existing transformer and for a new transformer, a comparison of which enables the determination of the most economical replacement year. The case studies conducted using both methods demonstrate their reliability for determining transformer end of life for assessing the appropriate time for replacement. Diagnostic test data for 90 working transformers were used to develop three methods of estimating the health condition of a transformer, which utilities and industries can use in order to assess the health of their transformer fleet. The first method is based on building a linear relation between all parameters of diagnostic data in order to determine a transformer health index, from which the health condition of the transformer can be evaluated. The second method depends on the use of artificial neural networks (ANN) in order to find the health condition of any individual transformer. The diagnostic data for the 90 working transformers together with the health indices calculated for them by means of a specialized transformer asset management and health assessment lab, were used to train an ANN. After the training, the ANN can estimate a health index for any transformer, which can be used in order to determine the health condition of the transformer. The third method is based on finding a relation between the input data and the given health indices (calculated by the specialized transformer asset management and health assessment lab) using the least squares method. This relation then can be used to find the health index and health condition of any working transformer. The health condition determined based on these methods shows excellent correlation with the given health condition calculated by the specialized transformer asset management and health assessment lab.

The design, simulation, and measurement of two bulk-driven down-conversion mixers with on-chip transformer baluns in 0.18 μm CMOS is presented. Applying either the RF signal or the local oscillator (LO) signal to the bulk connection of the transistors allows the amplification and switching stages of a conventional mixer to be combined into a single stage, thus improving the voltage headroom of the mixer. The addition of a transformer balun to the mixers improves the input impedance match, provides passive voltage gain, and performs single-ended to balanced conversion. A semi-analytical power-series analysis of the mixers is also presented. The mixer in which the RF signal is applied to the gates of the mixing transistors achieves a measured input-referred 1-dB compression point (P1dB) of −14 dBm, an input-referred third-order intercept point (IIP3) of −5.2 dBm, a gain of 13.6 dB, a noise figure (NF) of 26 dB, and an LO-to-RF isolation of 50 dB. The overall performance of both mixers is found to be comparable with other CMOS mixers, but with a higher noise figure (which can be mitigated with a high gain low-noise amplifier (LNA)).

Automation of the industrial transformer core assembly process is highly desirable. A survey undertaken by the author however, revealed that due to the high cost of existing fully automated systems, Australian manufacturers producing low to medium transformer volumes continue to maintain a manual construction approach. The conceptual design of a cost-effective automation system for core assembly from pre-cut lamination stacks was consequently undertaken. The major hurdle for automating the existing manual process was identified as the difficulty in reliably handling and accurately positioning the constituent core laminations, which number in their thousands, during transformer core construction. Technical evaluation of the proposed pick-and-place core assembly system, incorporating two mobile robots bearing a common gripper, is presented herein to address these requirements. A unique robotic gripper, having the capability to selectively pick a given number of steel laminations (typically two or three) concurrently from a stack, has the potential to significantly increase productivity. The only available avenue for picking multiple laminations was deemed to be a gripper based on magnetism. Closed form analytical and finite element models for an electromagnet-stack system were contrived and their force distributions obtained. The theoretical findings were validated by experiment using a specially constructed prototype. Critical parameters for reliably lifting the required number of laminations were identified and a full scale electromagnet, that overcame inherent suction forces present in the stack during picking, was subsequently developed. A mechanical docking arrangement is envisaged that will ensure precise lamination placement. Owing to the grippers unwieldy length however, conventional robots cannot be used for assembling larger cores. Two wheeled mobile robots (WMRs) compliantly coupled to either end of the gripper could be considered although a review of the current literature revealed the absence of a suitable controller. Dynamic modelling for a single WMR was therefore undertaken and later expanded upon for the dual WMR system conceived. Nonlinear adaptive controllers for both WMR systems were developed and subsequently investigated via simulation. Neglecting the systems dynamics resulted in analogous, simplified kinematic control schemes, that were verified experimentally using prototypes. Additional cooperative control laws ensuring the synchronisation of the two robots were also implemented on the prototype system.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The Smart Grid is an initiative to make the existing utility grid more effective and efficient by making utility infrastructure smarter. The initiative affects all areas of the utility grid and all utility hardware. Communication to utility hardware for monitoring and remote configuration is central to the smart grid vision. The focus of this project is the Smart Transformer, a distribution transformer with built-in intelligence and communication capabilities. Data acquisition and remote configuration hardware and software was developed and installed on a distribution transformer for application in deep rural areas. The solution included communication capabilities and adheres to industry standards. The solution was tested and data acquisition and management were done using the OSIsoft PI System software. Field tests were performed to evaluate the effectiveness of the solution in a deep rural setting. It was found that the smart transformer can be effectively monitored, configured and controlled in a deep rural setting. The smart transformer concept was investigated in a microgrid context. The potential of a smart transformer within a microgrid was explored and the smart transformer as a microgrid market-enabler was focussed on. A simulation was performed to evaluate the role of a smart transformer as a microgrid market-enabling device. It was found that the smart transformer has the potential to serve as a market-enabling device. / AFRIKAANSE OPSOMMING: Die slim kragnetwerk is 'n initiatief om die bestaande kragnetwerk meer effektief en doeltreffend te maak deur kragnetwerk infrastruktuur se intelligensie te vermeerder. Die initiatief beïnvloed alle aspekte van die kragnetwerk en kragnetwerk hardeware. Kommunikasie met kragnetwerk hardeware vir moniteering en instelling oor 'n afstand is sentraal aan die slim kragnetwerk visie. Die fokus van hierdie projek is die slim transformator, 'n distribusie transformator met ingeboude intelligensie en kommunikasie vermoëns. Data verkryging en afstandelike instelling hardeware en sagteware was ontwikkel en installeer op 'n distribusie transformator vir toepasing in diep-landelike gebiede. Die oplossing sluit kommunikasie vermoëns in en voldoen aan industrie standaarde. Die oplossing was getoets en data verkryging en bestuur was geïmplementeer met gebruik van OSIsoft se PI Stelsel sagteware. Veldtoetse was gedoen om die effektiwiteit van die oplossing in diep-landelike gebiede te evalueer. Dit was gevind dat die slim transformator effektief gemoniteer, ingestel en beheer kan word in 'n diep-landelike omgewing. Die slim transformator konsep was ondersoek in 'n mikro-kragnetwerk konteks. Die potensiaal van 'n slim transformator binne 'n mikro-kragnetwerk was verken en die vermoë van 'n slim transformator om 'n mark binne 'n mikro-kragnetwerk in staat te stel was op gefokus.‘n Simulasie was uitgevoer om die vermoë wat 'n slim transformator het om 'n mark binne 'n mikro-kragnetwerk in staat te stel te evalueer. Dit was gevind dat 'n slim transformator die vermoë het om 'n mark binne 'n mirko-kragnetwerk in staat the stel.

abstract: Dynamic loading is the term used for one way of optimally loading a transformer. Dynamic loading means the utility takes into account the thermal time constant of the transformer along with the cooling mode transitions, loading profile and ambient temperature when determining the time-varying loading capability of a transformer. Knowing the maximum dynamic loading rating can increase utilization of the transformer while not reducing life-expectancy, delaying the replacement of the transformer. This document presents the progress on the transformer dynamic loading project sponsored by Salt River Project (SRP). A software application which performs dynamic loading for substation distribution transformers with appropriate transformer thermal models is developed in this project. Two kinds of thermal hottest-spot temperature (HST) and top-oil temperature (TOT) models that will be used in the application--the ASU HST/TOT models and the ANSI models--are presented. Brief validations of the ASU models are presented, showing that the ASU models are accurate in simulating the thermal processes of the transformers. For this production grade application, both the ANSI and the ASU models are built and tested to select the most appropriate models to be used in the dynamic loading calculations. An existing application to build and select the TOT model was used as a starting point for the enhancements developed in this work. These enhancements include:  Adding the ability to develop HST models to the existing application,  Adding metrics to evaluate the models accuracy and selecting which model will be used in dynamic loading calculation  Adding the capability to perform dynamic loading calculations,  Production of a maximum dynamic load profile that the transformer can tolerate without acceleration of the insulation aging,  Provide suitable output (plots and text) for the results of the dynamic loading calculation. Other challenges discussed include: modification to the input data format, data-quality control, cooling mode estimation. Efforts to overcome these challenges are discussed in this work. / Dissertation/Thesis / M.S. Electrical Engineering 2011

Travelling wave fault locators (TWFL) have the possibility to get rid of the limitation of typical locators based on the 50Hz impedance. Their principles were invented in the early 1900's, but only recently became economically viable. Some TWFL devices are now commercialized.Despite the recent commercialization of TW fault locators, actual field experience of TWFL is hard to acquire and rarely presented in the literature. Due to this, most studies are based on simplified simulation models.Practical experience in the form of TW records are important. It is the basis to understand the practical difficulties of applying TWFL algorithms. It is also necessary to illustrate the simulations limitations, and to test algorithms on real records.The work performed in this thesis was supported by Siemens with the hope to develop TWFL devices based on the results. The aim of the work was first to acquire experience in the practical side of TWs and their recording in substations. Based on this practical experience, the second objective was to study a TWFL that includes a new method for wave detection: the pattern recognition algorithm (PRA). The practical experience was acquired with a measurement campaign performed in the Belgian transmission network, and with laboratory tests that reproduce the measurements of currents inside a substation.Fault records suitable to TW studies were acquired during the measurement campaign, and are analysed in this report. The fault records and the laboratory tests highlighted and characterized the impact of the substation measurements on the waves recorded. Modelling those measurement systems is shown to improve the accuracy of the simulation tools.This report also presents a theoretical development of the PRA. The algorithm is adapted to take into account the practical difficulties previously analysed. An applicable version of the algorithm is proposed and tested. The algorithm proposal provides a precision better than 300m when applied to the simulation models. This precision varies with the set of parameters used, with the line topology, and with the fault location. On the field record acquired, the algorithm provides the fault location with a precision of 110m.A prototype has been developed by Siemens, and some devices have been installed at the end of this thesis. The TW records that will be acquired by those prototypes will provide a significant help in continuing the work presented in this report. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

abstract: For the solid-state transformer (SST) application, a three-stage configuration consisting of a PWM rectifier based AC/DC stage, a dual active bridge (DAB) converter based DC/DC stage and a PWM inverter based DC/AC stage offers several advantages. For single-phase SST, the instantaneous input and load power seen by the DC/DC stage varies from zero to twice the load average power at double the line frequency. Traditionally, with phase-shift control, large DAB DC link capacitors are used to handle the instantaneous power variation of the load, with the DAB converter processing only the load average power resulting in better soft-switching range and consequently high efficiency. However, the large electrolytic capacitors required adversely affect the power density and the reliability of SST. In this thesis, a PWM control is used for the DAB converter in SST, which extends the ZVS range of DAB and allows the DAB converter to handle the pulsating power while maintaining/improving efficiency. The impact of the output capacitance of switches with PWM control is discussed for practical implementation. A 40kHz, 500W DAB converter is designed and built, and the experimental results proves that the DAB converter with PWM control in SST can achieve comparable efficiency while the DC link capacitors of SST can be reduced to a value that electrolytic capacitors are not required. / Dissertation/Thesis / M.S. Electrical Engineering 2012