In this thesis catastrophe theory is applied to the voltage stability problem in power systems. A general model for predicting voltage stability from the system conditions is presented and then applied to both a simple 2-bus explanatory power system and to a larger more realistic power system. The model is based on the swallowtail catastrophe which with its three control variables is able to determine the voltage stability of the system. The model is derived directly from the systems equations. The voltage stability of the system at each specified system bus is determined by comparing the values of the swallowtail catastrophe control variables with those of the unique region of voltage stability. The control variables are calculated from the system operating conditions. If the control variables specify a point inside the stability region, the system is voltage stable; otherwise it is voltage unstable. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Transformers are essential components facilitating transmission and distribution of electric power. Energisation of transformers, however, can cause core operating at deep saturation region and thereby induce transient inrush currents of high magnitude and with rich harmonics. This can lead to undesirable effects including potential damage to the transformer itself, relay mal-operation, harmonic resonant overvoltages, and reduced power quality in the system (mainly in the form of voltage dips). This thesis investigates voltage dips caused by energising generator step-up (GSU) transformers and two types of generation connection are studied: one is a combine cycle gas turbine (CCGT) plant connected to a 400 kV transmission grid and the other is a large offshore wind farm connected to a 132 kV distribution grid. To carry out the investigation, detailed network models were developed in alternative transients program/electromagnetic transients program (ATP/EMTP) and validated with the help of field measurements. For the connection of generation in the transmission grid, deterministic assessment was conducted to comparatively analyse voltage dips caused by energising large GSU transformers under different energisation conditions and different network conditions; special attention was paid to the energisation cases involving sympathetic inrush between transformers by addressing its prolonging effects on voltage dips, with sensitivity studies further carried out to identify the key influential parameters. In addition, stochastic assessment was conducted by applying Monte Carlo method, which helps identify the dip frequency pattern and the likelihood of reaching the dip magnitude resulted from the commonly agreed worst case energisation condition; their sensitivities to the variation of circuit breaker closing time span, transformer core residual flux, system condition and the number of transformers being energized together were also investigated. Furthermore, possible cost-effective operational approaches to mitigate the voltage dips were explored and compared. For the connection of large offshore wind farm, voltage dips caused by energising wind turbine transformers under different scenarios were assessed; in particular, sympathetic inrush between wind turbine transformers were studied, and the energisation sequence resulting in less sympathetic inrush was deterministically identified and stochastically validated. The simulation results of deterministic studies indicate that, when carrying out energisation of a large GSU transformer in the transmission grid under the commonly agreed worst case energisation condition, the dip magnitude can reach 9.6% and the duration 2.7 seconds; moreover, when coupled with sympathetic inrush, the duration can be prolonged by 136%, lasting for 6.4 seconds. The sensitivity studies show that transformer core saturation inductance is the key parameter determining dip magnitude and transformer copper losses is the key parameter determining dip duration. Stochastic assessment of voltage dips shows that, out of 1000 stochastic dip events, less than 0.5% of the dips can reach the worst case dip magnitude and about 80% are of magnitudes less than 0.6 pu of the worst case dip magnitude; the dip frequency pattern is found to be insensitive to the circuit breaker closing time variation but can be considerably influenced by the residual flux distribution. In terms of mitigation measures, it was proven that, by adjusting tap changer position, applying static var compensator and even opening coupler circuit breaker in the substation, the degree of voltage dip especially the dip duration can be significantly reduced. Contrasting to those observed in the transmission grid, voltage dips resulted from energising wind turbine transformers in large offshore wind farms are of less concern; dip magnitudes are no more than 1% in the case of energising a stand-alone wind turbine transformer. However, sympathetic inrush between wind turbine transformers within one feeder was found to be significant and the energisation sequence resulting in less sympathetic inrush is to separately energise the wind turbine transformer from the one closest to the offshore platform to the one farthest away from the platform.

Power quality related problems cause large financial losses in the order of billions worldwide. The evaluation process aimed at determining effective remedial actions starts with the correct identification and characterization of power quality disturbances. Measurements performed in the electrical power network and the corresponding collection and process of data are the primary method of characterization of the phenomena. The ideal deployment of monitoring devices would entail a monitor installed at each node of the network so that the power quality throughout the system could be directly assessed. In reality, however, technical and mostly economical constraints limit the number of monitors a network operator can install in the system. Power quality at non-monitored sites, therefore, has to be estimated by extrapolating the data from monitored sites. Consequently, it is crucial to identify the sites that provide the most accurate picture of the system’s overall power quality. Unfortunately, no recommended practices or guidelines for determining the minimum number and the best locations for optimal power quality monitoring have been prescribed in standards or reports. This thesis investigates voltage sag monitoring as part of a larger power quality monitoring scheme. The aim is to develop a methodology for optimal monitor placement for fault location and sag estimation. The thesis, divided in four main parts, focuses on network sag performance estimation and optimal monitor placement for fault localization and sag estimation. The introductory part of the thesis gives an overview of power quality surveys conducted around the world in recent years with special emphasis on the monitor placement criteria used. It also summarizes the main methods for network sag performance estimation proposed to date. The main part of the thesis firstly reviews the most referred optimal monitor placement method for sag estimation proposed in academia, highlighting its limitations. Then a robust fault location algorithm is proposed to enhance this method and overcome the identified limitations. The enhanced method is thereafter used as the basis for the generalization of one of the leading methods for optimal monitor placement for fault location in the second part of the thesis. The formulation of its optimization problem is extended for application in large power networks by adapting the modeling approach for the sag monitor placement problem. To reduce the high computational and memory burden associated with finding the optimal fault location monitor program, the thesis introduces a less memory intensive heuristic search algorithm in the third part of the thesis. A series of custom objective functions are proposed to be used with this algorithm to find optimal fault location and sag monitoring programs aimed at estimating the most critical events for customers. In the final part of the thesis, the main concepts and techniques introduced in the first three sections are combined to develop a synergistic approach to optimal monitor placement for sag characterization based on fault location. The suitability of the new method for techno-economic assessment of voltage sags using strategically or conventionally deployed monitors is established.

Calcium entry through voltage-gated calcium (CaV) channels is important in diverse cellular processes including neurotransmitter release, gene expression and cardiac pacemaker activity. CaV channels auxiliary CaVβ subunits enhance plasma membrane expression and modify the biophysical properties of CaVα1 subunits. Due to their multi-domain structures - including a conserved SH3-GK 'core' and hypervariable N- and C- terminal domains - CaVβs are also considered to be members of the membrane-associated guanylate kinase (MAGUK) family of scaffolding proteins, and may therefore act as molecular scaffolds both within and outside the CaV channel complex. This project studied the roles of CaVβ N- and C-terminal hypervariable domains in contributing to isoform-specific differences in CaVβ functions both in a) CaV channel complex expression and distribution, and b) interactions with non channel proteins. To analyse such contributions a series of molecular tools were developed to assess the distributions of CaVβs (both within and outside the CaV channel complex) and their interactions with novel potential partner proteins. This involved systematically testing fluorophore- and epitope-tagged CaVβs for co-localisation with both fluorophore-tagged CaV2.2 and a range of myc-tagged potential interaction partners (as quantified either by a 'Membrane Localisation Index' developed during this project or Intensity Correlation Analysis). This approach uncovered much detail about relative isoform specificities of CaVβ non-channel complex protein-protein interactions, however one particularly striking interaction was discovered between CaVβ1b/CaVβ4 and the nuclear protein Heterochromatin 1 γ (HP1γ), where nuclear translocation of CaVβ1b or CaVβ4 was induced upon association with HP1γ. Given the similarity of CaVβ1b and CaVβ4 N termini, a series of CaVβ1b N-terminal chimeras were then created, where the N terminus was exchanged with that of CaVβ3 (which did not interact with HP1γ). Subsequent imaging studies using these chimeras then confirmed that the CaVβ1b N terminus is necessary for co-localisation with HP1γ and subsequent HP1γ mediated CaVβ nuclear uptake. Given that an interaction between the CaVβ3 isoform and Pax6(S) - another nuclear protein - have been reported, where the CaVβ3-Pax6(S) interaction also induces nuclear translocation of both proteins, the CaVβ1b/CaVβ4-HP1γ interaction may represent one of a range of as-yet undiscovered CaVβ1b/gene regulatory protein interactions. As interaction with CaVβ3 suppresses the transcriptional activity of Pax6(S), nuclear targeting may be an important means by which CaVβs modulate gene expression - which in the case of HP1γ interactions may occur via de-repression.

This master’s thesis deals with the design of integrated voltage regulator. Topologies of linear voltage regulators and their stability are discussed. Part of the thesis deals with description and simulation of blocks of selected regulator topology. The thesis describes the difficulties of integrated circuit design in the automotive industry. The electrical scheme of the designed regulator is explained. The work also focuses on the stability of designed regulator. Then presents simulations. It discusses the layout of integrated circuits and the designed voltage regulator.

This master thesis deals with designing of a recuperative converter system and auxiliary circuits that extend the life of the automotive battery by using supercapacitor as a source of power when starting a car using the start-stop function. The microcontroller is used to measure important circuit values and control the output current of the converter.

Lightning is one of the main factors that cause Photovoltaic (PV) systems to fail. The PV modules inside PV systems, like any other electric equipment, will be degraded under electrical stress. The effect of electrical degradation of the PV modules caused by lightning induced voltage has been rarely reported. In the dissertation, the electrical properties degradation of a polycrystalline silicon module was studied. Firstly, lightning impulse voltages of positive polarity ranging from low to high are applied on different groups of the testing modules. All these lightning impulse voltage tests are conducted in the same experimental condition except for their stress voltage magnitudes. The maximum power output, I-V characteristics, and dark forward I-V curve are measured and reported periodically during the lightning impulse voltage tests. By comparing the maximum output power and changes in the internal electrical properties, it could be concluded that lightning impulse voltages, even medium voltage levels, will cause degradation to the sample. The relationship of the maximum output power and the number of applied impulses for different testing voltage levels are compared. An analysis of the electrical property changes caused by the lightning impulse voltages is presented. Secondly, a group of samples are tested with lightning impulse voltage of negative polarity. A comparison of the impulse voltage aging effects at the same voltage level with positive polarity is made. The maximum power output drop caused by positive and negative lightning impulses are compared. Laboratory results revealed that positive and negative lightning impulses will not only influence the degree of degradation, but also lead to different electrical property changes. Finally, a comparison of the effect of lightning impulses combined with other stress factors are discussed. The study simulates a field-aged sample’s behavior at lightning impulse voltage testing conditions. The result suggests that the degradation caused by lightning impulse voltage is greatly accelerated when the sample has bubbles and delamination. Electrical breakdown of the module is caused by the failure of the insulation.

This thesis is based on the investigative studies performed on fiberglass crossarm, which will be used in the distribution line structures as an additional insulation component. Lightning impulse voltage tests were conducted on the fiberglass crossarm alone to determine its critical flashover (CFO) voltage, and also the critical flashover voltage of 15 kV polymer suspension insulator plus the fiberglass crossarm. The Added CFO voltage of the fiberglass crossarm to the insulator was determined with polymer suspension insulator as the primary insulation component and the fiberglass crossarm as the secondary insulation component. Added CFO voltage was evaluated for 1 ft through 5 ft length of the fiberglass crossarm for positive and negative polarities, under dry and wet condition. The thesis also presents a comparison of the obtained results made with the previous results of the wood crossarm and polymer crossarm with the polymer suspension insulator.

The main objective of the research was the fabrication and characterization of MOS/MIS capacitors with ZnO as the insulating layer. Comparison with the already well known behavior of MOS/MIS capacitors with SiO2 as insulator was used to facilitate determination of the ZnO characteristics. Moreover, thermal annealing of the samples led to increased understanding of the role of defects on the dielectric properties of the ZnO layers in the MOS/MIS devices. Hall-effect transport measurements and x-ray diffraction (XRD) spectroscopy are used to analyze the structure and electronic surface characteristics of the ZnO insulator. Capacitance-voltage (C-V) measurements are used to understand the effect of surface interface charges and fixed oxide charges in the MOS/MIS (metal-oxide (insulator)-semiconductor) capacitor. The results of the Hall-effect measurement will reveal several things; the sheet resistance, carrier concentration, and mobility as well as confirm the type of silicon used. The optical spectrophotometry measurement confirmed the band gap of 3.2 eV for ZnO. The x-ray diffraction data confirmed a (002) orientation polycrystalline wurtzite ZnO structure. Initial capacitance-voltage measurement of SiO2 and ZnO revealed that the capacitance was larger for SiO2 than for ZnO. This study also explores the impact of thermal annealing on the performance of the ZnO capacitors. Hall-effect measurements are used to evaluate the influence of thermal annealing on the resistivity, carrier concentration and mobility as a function of annealing temperature. ZnO is an n-type semiconductor; this n-type conductivity is due to deviations from the stoichiometry as a result of oxygen vacancies and interstitial zinc. After ZnO samples were annealed at different temperatures, the Hall-effect measurements were performed. After thermal annealing, the mobility increased significantly by two orders of magnitude, but both the carrier concentration and the sheet density decreased. A threshold voltage (turn-on) of -1V was observed for the ZnO sample annealed at 980oC. ZnO is very versatile material with the potential for use in field effect transistors, solar cells, sensors, surface acoustic wave devices and photodiodes due to the high conductivity and high transmittance in the visible part of the spectrum. ZnO as an insulator works through analytical solutions, but not necessarily through this investigation. The difference in oxide thickness during rf magentron sputtering change the capacitance for ZnO making it lower. For n-type substrates it appears that the capacitance after annealing was higher than the capacitance before annealing. After annealing, a stretched out capacitance-voltage curve indicates the presence of trapped oxide charges and an unsmoothed surface. A high resistivity material could be used for some devices. However, typically low resistivity materials are used. After ZnO samples were annealed (unetched) at different temperatures, the Hall-effect were performed and the mobility increased significantly by two orders of magnitude, but the sheet density decreased along with the carrier concentration. The only sample that appears to come to a high frequency C-V in equilibrium is the ZnO sample annealed at 980oC. The depletion region was distinguishable and the transition point (threshold voltage) was found to be at -1 V.

The objective of this project is to present a Lithium Ion battery voltage model derived using systems engineering principles. This paper will describe the details of the model and the implementation of the model in practical use in a power system. Additionally, the model code is described and results of the model output are compared to battery cell test data. Finally, recommendations for increased model fidelity and capability are summarized. The modeling theory has been previously documented in the literature but detailed implementation and application of the modeling theory is shown. The detailed battery cell test voltage profiles are proprietary; as such this project will not include axis values, often used in presentation of proprietary data in the public domain. The objective of this presentation is still achieved, as the modeling implementation and results are clearly demonstrated.