The rate at which the integration of distributed generation (DG) penetrates the public power supply has started to put various demands on the distribution system, since they are directly connected to the network. Distribution level protection is based on a time-overcurrent design. The design is to clear faults with as little impact and minimum time on the equipment and the customer. The increasing demands placed by grid services on the DGs, especially the PV types have a serious impact on the distribution system. For example, special protective devices are required to prevent the risk of danger in the event of mains interference. In this thesis, the main focus was on the contribution of fault currents to the distribution networks, and how the high penetration of DGs especially the renewable energy resources (R.E.S.) types affect the coordination of overcurrent (O.C.) protection. In view of the changes in the international regulations, the DGs are expected to stay connected and perform grid-related control functions, instead of shutting down at the first sign of a fault. This problem becomes more acute when the DGs stay connected during faults, known as voltage ride through (VRT). This thesis presented its findings on the impact of the DGs of various types of DGs (synchronous generator, asynchronous and power electronic) on the protection coordination by the high increase of fault currents, and the mitigation techniques of the impact of the inverter interfaced DGs (whose fault current contribution was not so high) on the overcurrent protection. The impact on system’s over-current protection coordination in such hybrid AC and DC microgrid, how the fault current changes by the high penetration of DGs in the hybrid microgrid and their effects on the protection over-current coordination were presented, as the name microgrid was adopted for networks having a point of common connection (PCC). The inverter interfaced-equipment were never in the conventional systems, the few that were there were all on the load side of the distribution system. The inverter interfacing DGs (PVs) and the synchronous types are the types of DGs that affect over-current protection of the distribution system and these were mitigated accordingly, considering the first few cycles of the fault events of the ride through capabilities. The analysis of the different penetration levels of the DGs in an existing 33kV in the Nigerian distribution network, (CocaCola-Challenge Industrial feeder) was thoroughly analysed, for less than 20%, more than 60% and 100% of the feeder load. Most of the DGs, presently existing in that network are the synchronous types, but they are only used as standby sources of power, and the renewables (RES) like the photovoltaics (PV), run of flow (RoF) Hydo and the wind turbine generators (WTG) are proposed additions. The objective of this thesis was to explain the fundamentals of distribution generation (DG) and especially the RES, in relation to distribution protection relay coordination to see why there should be urgency in carrying out the study especially in a developing environment where the grid is unstable, the load is rapidly expanding and RES is intermittent. The radial distribution system (DS) with high penetration of DG was introduced. The motive was to critically investigate protection coordination problems and the solutions to the problems. The main objective was to optimally recommend the type, size and location of the DG for an actual distribution feeder in an unstable environment where the grid supply is not steady. The effect of 100% and above of feeder load penetration on such feeders formed the objective of this research. The literature review which was for investigating in greater details the technical aspects of the operation and control of the high penetration of RES in the distribution system were thoroughly analysed. The review of the existing radial distribution protection system and the effects of high penetration of DG on the protective relaying were thoroughly investigated. The issues of power electronic based inverters and the protection coordination problems, were investigated. The protection coordination as regards to fault level changes and grounding, intentional and un-intentional islanding were major important aspects which were treated in the technical review.

The main topic of this Master's Thesis is design and implementation of mechanical connection between the automatic range switch unit and the AC-DC Transfer Standart Fluke 792A. This Master's Thesis contains theoretical analysis of the the AC-DC Transfer Standart Fluke 792A and of stepper motors. Followed the choosing of appropriate drive. In next chapter is the theoretical analysis of automatic range switch unit, used microcontroller and the description of the GPIB. Last part of this Master's Thesis describes design of mechanical connecting part and the selection of appropriate sensors for sensing the current position of the shading component.

The main topic of this Master's Thesis is design and implementation of automatic range switch AC/DC Transfer Standart Fluke 792A. In the first part is introduce and description of character and the parameters AC/DC trasfer Standart Fluke 792A and design of the Automatic range switch for this equipment. In the next part is introduce design and description of realize automatic switch control unit it has comunication faculty witch PC over GPIB bus. In the finish part is show of the theoretic description for GPIB bus and her realization with helped microcontroller Atmega16.

I och med att båtar har med tiden blivit allt mer tystare både akustiskt och magnetiskt, är det av stort intresse att mäta den elektriska signaturen. Den elektriska signaturen uppstår fram för allt från den galvaniska effekten mellan båtens skrov och propeller och ger upphov till en potentialskillnad. Denna potentialskillnad propagerar i vattnet med en väldigt låg frekvens (0-3kHz). Med hjälp av specifika undervattensensorer kan dessa signaturer mätas för att detektera och lokalisera båtar. Varje sensor måste kalibreras i dess rätta omgivning (vatten) på grund av deras individuella geometri. För kalibreringen behövs ett känt homogent elektrostatiskt fält användas som referens. Examensarbetet avser att modellera den faktiska vattentanken som är tänkt som kalibreringsanläggning för sensorerna och simulera det elektrostatiska fältet som uppstår. Examensarbetet har ett ingående tillvägagångsätt för hur modellen och simuleringen implementeras i COMSOL Multiphysics® 5.5 som baseras på den finita elementmetoden (FEM). Ett teoretisk homogent elektriskt fält är svårt konstruera i verkligheten, därför är examensarbetet huvudsyfte att analysera homogeniteten för praktiska elektriska fält som finns i vattentanken. Olika konfigurationer av hur laddningsplattor fördelas simulerades och analyserades. Den väsentliga slutsatsen från simuleringarna är att homogeniteten på det elektriska fältet är bra så länge laddningsplattorna är symmetriska mot varandra men på en bekostnad av att fältstyrkan minskar. Examensarbete inkluderar även simuleringar hur undervattensensorn i sig själv påverkar det elektriska fältet som den skall kalibreras i, sensorn introducerar en störning. Slutligen finns det förslag för förbättring av arbete och förslag för ett fortsatt arbete. / With time, boats have become more quiet, both acoustic and magnetic. Therefore, it is of great interest tomeasure the electric signature. The electric signature is a low-frequency (0-3 kHz) electric field generatedby a potential difference that appears due to the galvanic effect between the boat's hull and propeller.With assistance from specific under-water sensors, these signatures can be measured to detect andlocalize boats. Due to the individual geometry of the sensors, each sensor must be calibrated in its rightenvironment (water). To perform this, a known homogeneous electrostatic field must be used forreference. This master Master-degree project purpose is to modulate a water tank, which is supposed to beused as a calibration facility for the sensors and simulate the electrostatic field that will evolve. Thisproject presents the approach for how the model and simulation will be implemented in COMSOLMultiphysics® 5.5, which is based on the finite element method. A theoretically homogeneous electricfield is difficult to build in reality, hence this project main objective is to analyse the homogeneity forpractical electric fields in the water tank. Different electric fields were analysed depending how the metalplates were distributed. The main conclusion from the simulations is that the homogeneity on theelectrical field is good enough to use for calibration purposes. The plates shall to be symmetricallydeployed with respect to each other. A drawback is that the field strength decreases when parts of thefield diverts. This project also simulates how the under-water sensor itself affects the electrical field it issupposed to be calibrated in; the sensor introduces disturbances to the field. Finally, this report proposesseveral improvements as well as direction for further work.

Urban rail systems such as subways and trams transport millions of people every day, oering a high level of service. Most of these systems are fed by direct current (DC). The design of the power supply network of DC electried transit railways is of great importance and requires the use of simulation models. The power supply network is composed of a high voltage network (fed with AC) linked to a traction network (fed with DC) by traction substations. Many simulation models ignore the high voltage network in the design process whereas it has a signicant inuence on the results. A Newton-Raphson algorithm is implemented to solve the AC load ow in the high voltage network, and coupled to the existing simulation software Symphonie. Three dierent high voltage network architectures are simulated, and the simulation results are analyzed. The results show that the voltage drop at the AC side of traction substations and the load sharing between them varies signicantly from one architecture to another. In particular, when several traction substations are connected to the same high voltage loop, voltage drops can be signicant for some traction substations. In conclusion, the design of the power supply network of DC electried transit railways requires the simulation of the high voltage network when several substations are connected to the same high voltage loop. / Publika sparburna transportsystem sasom tunnelbanor och lokalbanor transporterar miljontals manniskor varje dag. De esta korta linjer matas med likstrom. Utformningen av stromforsorjningen till dessa system ar avgorande for ett val fungerande , och forutsatter anvandningen av olika matematiska modeller. Detta natverk bestar av ett vaxelstroms hogspanningsnat som omformas till likstrom i era banmatningsstationer langs banan. Dessa matematiska modeller ignorerar dock ofta hogspanningsdelen i modelleringen, varfor resultatet ibland kan bli missvisande. I detta arbete har en belastningsfordelningsalgoritm baserad pa Newton-Raphsons metod implementerats for att skapa en battre modellering av hsgspanningsdelen i den bentliga programvaran Symphonie. Tre olika hogspanningsstrukturer har bearbetats och resultatet visar att spanningsfall och belastningsf ordelning varierar mellan de olika strukturerna. Speciellt nar era transformatorstationer ar kopplade till samma hogspanningssystem, kan spanningsfall vara patagligt for vissa transformatorstationer. Sammanfattningsvis maste utformningen av hogspanningsystemet till likstromsforsorjda jarnvagar utformas med hjalp av anpassade matematiska modeller som tar hansyn till placering av transformatorstationer liksom hogspanningsnatets kapacitet.

Electromagnetic based energy harvesting systems such as Variable reluctance energy harvesting systems (VREH) have shown to be an effective way of extracting the energy of rotating parts. The transducer can provide enough power to run an electronic sensing system, but the problem arises in finding an efficient way of rectifying that power to generate a stable energy supply to run a system, which this report will investigate. Active and passive voltage doublers have proven to be a suitable candidate in solving this issue due to the simplicity and the small footprint. This thesis will aim to compare active and passive voltage doublers under various scenarios in order to understand under which circumstances are active or passive voltage doublers to be preferred. From the conducted experimental measurements, this thesis concluded that active voltage doublers are recommended during high RPMs (>10 RPM) while passive voltage doublers (especially fullwave voltage doubler) is recommended at lower RPMs. Quality of power also plays a significant role in this study. Therefore, measurements have also been done for ripple and rise time. From the measurements, this thesis can conclude that the overall power quality was the best in Full-wave voltage doublers, while Active-voltage doublers had lower ripple than FWVDs at higher current loads.

Ce travail concerne l'étude théorique,l’analyse numérique et la validationexpérimentale d'une topologie de convertisseurd’électronique de puissance basée sur unconvertisseur multiniveau modulaire entrelacéavec transformateur moyenne fréquence.L’architecture est adaptée pour l’étage deconversion AC-DC dans les applications detransformateur d'électronique de puissance pourla connexion entre un réseau alternatif moyennetension et un réseau continu basse tension.L’entrelacement réduit les pertes par conductiondans les interrupteurs. Le transformateurmoyenne fréquence 10 kHz assure une isolationgalvanique et connecte le convertisseurmultiniveau modulaire entrelacé à unconvertisseur pont complet. Avec comme pointde départ la structure, le principe defonctionnement, la modélisation, la technique demodulation et le schéma de commande sontdiscutés. Une caractéristique du convertisseur estla génération simultanée de la tension du réseaubasse fréquence et de la tension primaire dutransformateur moyenne fréquence.L'équilibrage de la tension des condensateurs etla minimisation du courant de circulation sontcombinés dans un seul algorithme. La commanderégule le courant alternatif et la tension du buscontinu, du côté haute tension, ainsi que latension continue et le flux de puissance, du côtébasse tension. La validation expérimentale duconvertisseur est réalisée avec un prototype de720 W monophasé à l’échelle réduite. Lesrésultats démontrent la stabilité du système decommande lors d'opérations en régimepermanent et dynamiques (pas de charge,inversion du flux de puissance). / This work aims to present thetheoretical study, the numerical analysis and theexperimental validation of a power electronicsconverter topology based on an interleavedmodular multilevel converter with mediumfrequencytransformer. The architecture issuitable for the AC-DC stage in solid-statetransformer applications for the connectionbetween a medium-voltage AC grid and a lowvoltageDC grid. The interleaving reduces theswitch conduction losses. The 10 kHz mediumfrequencytransformer provides galvanicisolation and connects the interleaved modularmultilevel converter to a full-bridge converter.From the converter structure, the principle ofoperation, the modeling, the modulationtechnique, and the control scheme are discussed.One feature of the converter is the simultaneousgeneration of the low-frequency grid voltageand the medium-frequency transformer primaryvoltage. The capacitor voltage balancing and thecirculating currents minimization are combinedtogether in a single algorithm. The controlsystem regulates the AC current and the DC busvoltage, on the high-voltage side, and the DCvoltage and power flow, on the low voltage side.The experimental validation of the converter ismade with a scaled-down single-phase 720 Wprototype. The results demonstrate the controlsystem stability in steady-state and dynamic(load step, power flow inversion) operations.

Thesis Abstract Current Nuclear Power Plant (NPP) design does not account for Beyond Design Basis Events (BDBEs) and thus lack the provisions to effectively mitigates complete loss of AC power and total loss of heat sink. Furthermore, parametric models used in PRA studies to assess Nuclear Power Plant’s safety risk for BDBE and External Events (EE) have significant limitations and proved ineffective to provide solutions on how to mitigate in BDBE or EEs situations. The Fukushima accident is a good example where PRA assessments did not provide the necessary means to cool or contain the reactors effectively. In this thesis, Emergency Mitigation Preparedness (EMP) model and assessment is proposed. The EMP model is objective and practical in evaluating NPP’s mitigation readiness in BDBE and EEs situations and provide a practical NPP Vulnerability indicator gauge which can potentially be used in risk-informed decisions. This will aid further in the NPP to improve in areas of emergency planning, enhance site and reactor design and improve workers safety and readiness to execute effective mitigation procedures and emergency plans. / Thesis / Master of Engineering (ME)

The present thesis deals with fault impact mitigation in grid connected converters used for High Voltage Direct Current transmission. Certain critical fault cases require additional obstructing protection actions to ease the impact on the converter valves. DC sided faults drives high fault currents through the converters. Single phase to ground faults at the converter AC bus results in overvoltages across the converter valve arms. The phenomenon of these faults are described both for symmetric and asymmetric configurations. Different available solutions are explained and evaluated. Simulations in PSCAD/EMTDC show the impact of the protection measures. A three phase short circuit introduced on the tertiary winding of the transformer is an effective temporary measure against the destructive fault cases. It is shown in this report that a tertiary shortcircuit will greatly reduce the overvoltages after converter bus faults and redirect a large part of the fault currents after DC faults. With the lower voltage on the tertiary winding, it is a suitable connection point for short circuit devices.

This thesis presents an optimal method of designing and controlling an oscillating energy harvesting system. Many new and emerging energy harvesting systems, such as the energy harvesting backpack and ocean wave energy harvesting, capture energy normally expelled through mechanical interactions. Often the nature of the system indicates slow system time constants and unsteady AC voltages. This paper reveals a method for achieving maximum energy harvesting from such sources with fast determination of the optimal operating condition. An energy harvesting backpack, which captures energy from the interaction between the user and the spring decoupled load, is presented in this paper. The new control strategy, maximum energy harvesting control (MEHC), is developed and applied to the energy harvesting backpack system to evaluate the improvement of the MEHC over the basic maximum power point tracking algorithm.