In this thesis a method was developed to evaluate and compare various offshore grid topology and capacity choices. A small power system was created for the purpose of the study, including prototypes of offshore grids. To perform the offshore grid study, preliminary steps had to be taken and four subtasks were thus defined:1. Develop a scenario of wind park sizes and locations.2. Obtain representative wind speed data for each of the locations defined.3. Calculate resulting wind power production, given the scenario and the wind speed data.4. Study wind power integration and effects of grid topologies.The North Sea was chosen as a starting point and offshore wind power scenarios for the North Sea in 2025 and 2030 were first developed. Choices regarding which wind data to base the study on, i.e. re-analysis data, numerical weather prediction data or synthetic wind speed data, were evaluated. It was chosen for the final analysis to use a relatively high resolution wind speed data set, resulting from metrological data modelling. This wind speed data was then matched with the wind park locations and the wind power production for the North Sea scenario calculated. A multiturbine approach was applied for this conversion from wind speed to wind power. Finally, the resulting wind power could be included in an offshore grid structure and integrated into a power system.A small power system was created including three main generation/ load areas based on the characteristics of the Norwegian, Dutch and the British generation portfolios. These areas where connected with link capacities according to the existing and planned HVDC links between the real countries. Three offshore wind areas where then added, interconnected and connected to their respective countries, creating an offshore grid structure. The benefits of different topologies were then investigated by varying the link capacities off the offshore grid structure. Simulations were performed using a unit commitment and economical dispatch simulation tool. The benefits were mainly evaluated in terms of wind integration, emission reductions and reductions in operational cost.All cases are compared with a base case having only radial connection of the offshore wind clusters. The meshed grid structure results in increased wind integration reduced emission and reduced operational cost for all of the cases. The offshore grid was further found to facilitate both wind integration and trade. Though increasing the rating of the interconnections to shore above the capacity of the connected wind park cluster, as to accommodate for additional trade, was not found to give additional benefits. Regarding the capacities of the interconnections between the wind park clusters, the benefits were seen to saturate at a rating equal to the capacity of the smaller of the two connected wind park clusters. As investment cost was not considered in this thesis, further decisions regarding the optimal rating of the cables were based on the assumption that a high link utilisation is desirable. It is however recommended to apply a cost-benefit analysis for more accurate evaluations. As could be expected the effects on the onshore generation were unevenly distributed among the created areas depending on the generation mix. Finally, it should however be noted that since the case study only included three areas and an un-optimised hydro-scheduling method, results should be treated with caution.

The addressed issue for this report is the making of a model, which represents the power system in Great Britain. This model is connected to an already existing model of Northern Europe in order to study how the present power systems are affected by eventual connections between Great Britain and Norway and the profitability of these. A model for 2020 is also created in order to study how increased wind generation are affecting such cables. Electricity trading in Norway is normally done through the Nord Pool exchange which also covers the other Nordic countries. Most of the electricity is traded in the Elspot market where hourly contracts are traded daily for physical delivery in the next day’s 24–hour period. The price for the volumes traded is based on the intersection between the supply and demand curves. Participants in Norway are normally trading their entire volumes at the exchange. This is distinct from trading in Great Britain where the base load and the ‘shape’ normally are traded separately. Electricity trading in Great Britain is based on bilateral agreements which allow direct contracting between counterparts. Each transaction is made independently between the parties involved, giving the customers an opportunity to negotiate the best price from suppliers and generators without being constrained by any official price. Models for both a 2010 and a 2020 scenario of the Great Britain power system are created in the EMPS-model. The EMPS model is a market simulator which optimizes the utilization of a hydro-thermal power system based on stochastic supply and demand. Great Britain is divided into four areas in both scenarios. Each area has defined transfer capacities to other connected areas while the transfer capacity within each area is unlimited. These areas are therefore defined in such a way that boundaries with insufficient transfer capabilities in the real system are located at the boundary between two areas in the model. Coal, gas, bio and oil fired plants are represented individually in the model while nuclear, wind, small scale CHP, hydro and pumped storage capacities are aggregated for each area. Meaning that there is only one aggregated nuclear plant, one aggregated wind farm etc. in each area. An area also has a given demand which varies throughout the week and year. Price calculations in the model are based on the intersection between the supply curve and the demand curve. Pricing in the model is therefore more representative for the way of pricing in Norway than in Great Britain.For the 2010 scenario, three different cable alternatives are simulated. Two of these cases are equal except for the landing area of the cables in Great Britain. One cable is connected to Southern England while the other is connected to Northern Scotland. For the third case, the assumptions are similar to the other cases except for an equalization of the gas price in Europe. The landing area for the cable in this case is Southern England. All three cable alternatives returns a fair-sized congestion rent, but the congestion rent is not sufficient to cover the investment cost for any of the discussed cables based on the defined assumptions. Additionally, the cables result in large grid constraints across the boundary between the landing area in Norway and the other Norwegian areas connected to this area. Increased constraints are also an issue for the cable connected to Northern Scotland.Towards 2020, installed wind capacity is expected to rise considerably. This also includes offshore wind farms such as Dogger Bank. A cable from Norway could therefore be connected to Dogger Bank and utilize spare capacity on the cable from Dogger Bank to Great Britain. Three different cables are discussed for the 2020 scenario. The first case is a cable from Norway to Southern England and the second and third case are cables from Norway to Dogger Bank. All three cables have the same transfer capacity. The difference between the two cables connected to Dogger Bank is the transfer capacity from Dogger Bank to Great Britain. The second case has a transfer capacity towards Britain which equalizes the installed wind capacity at Dogger Bank. For the third case, the sum of both the cable towards Norway and the one towards Britain equalizes the installed capacity at Dogger Bank. As for the cases in the 2010 scenario, none of these cable alternatives generate a congestion rent which is sufficient to make the cable profitable based on the defined assumptions.

This thesis deals with the development of self-sustained sensors based on non-conventional measurement techniques. The motivation behind this topic is to help utility companies reduce their fault handling time and improve the way faults are handled. As of today, the distribution system does not have widespread surveillance and automation systems in place. The thesis therefore investigates a sensor design based on Rogowski coils (RC), with both measurement and power supply capabilities.The concept of printed-circuit-board Rogowski coils (PCB RC) and conventional RCs for current measurement is presented. A theoretical, dimensional study with respect to feasibility and output signal magnitude is then performed. On basis of this analysis, a PCB RC prototype is manufactured. For the sensor to be implemented in the resonance grounded distribution system, it must be able to measure currents of low magnitude, as the fault current is compensated by Petersen coils. The prototype is therefore tested for common distribution system current values. Due to limitations during construction and design flaws, the PCB RC performance was poor. The induced voltage error, with respect to the theoretical response was 64.3 - 69.1 %.As the prototype's ability to supply enough power to the sensor circuitry (demand found to be > 10 mW) proved so limited, a more thorough analysis concerning the RC is presented. Obtaining this amount of power is, theoretically possible and easier with a conventional RC. Its maximum average power supply capability was found to be 10.4 mW during ideal conditions. Even better results can probably be obtained as well. Based on this RC, the complete sensor system is discussed. This include rectification, digitizing, integration and boosting of the RC voltage to 3 V for battery application. A survey of possible fault localization methods for resonance grounded distribution systems is presented and an implementation is suggested.Finally, the prototype is tested with short circuit currents of 30 kA amplitude. The performance was better than for the load current test, but the magnitude error was still substantial. It varied from 20 % to 40 %. However, the lab's signal integration showed that the prototype reproduced the applied current waveform accurately.The simulations, testing and analysis performed indicate that a RC can be used for both supply of power and measurements. However, a prototype should be manufactured in order to assess this thesis' theoretical results. Combined with the proposed auxiliary circuitry and implementation strategy, it can improve the utility's fault handling.

In this thesis work, different proposed methods for detecting and locating short circuit faults in Multi Terminal HVDC grids have been evaluated by implemenation and transient simulations in PSCAD. The research has been limited to cable based systems. HVDC grids have seen increasing interest in recent years, but have yet to be fully realised. Suitable converter technology was introduced in 1997 and has been further developed since, while switches able to interrupt large DC currents were introduced in June 2013. One of the major issues left is fault localisation. Due to the low impedance in HVDC cable systems, fault currents rise to severe magnitudes system wide in a matter of a few milliseconds. This may cause damage to the converter diodes if not dealt with quickly.In order to obtain a better understanding of the fault propagation, research into the subject is presented. It is found that the capacitors in the converters is a main source of large fault currents, and fast fault detection is essential for protection of converter components. Time between first detection of fault until current interruption should be within a few milliseconds. Different methods have been proposed for localisation of faults in recent years. These are presented together with traditional fault localisation methods, and briefly discussed with the intent of deciding which to implement and evaluate in PSCAD.Protection based on current derivative and wavelet transformation, as well as travelling wave protection is chosen and implemented in a three converter VSC system. Different fault types are applied at various locations with varying system capacitance and up to 16 $Omega$ fault impedance. The results indicate that none of the three methods are able to detect and locate all impedance faults on their own. The travelling wave protection is suitable for short lines, but fails when exposed to high fault impedances and distances. By using derivative polarity to determine direction of fault and wavelet magnitude to determine distance, faults are successfully located in a high capacitance system within a respectable time. It is concluded that all the three tested methods should be considered for implementation when designing a future HVDC protection system.

In this study, existing work, opportunities, standards and essential safety aspects on development of LVDC distribution systems have been considered. It can be summarised that the standard requirements for AC systems also applies to DC systems, and that one does not come apart DC-DC regulators in equipment due to the galvanic separation which is needed to fulfil the safety requirements. One of the main challenges of introducing an LVDC system is the non-existence of building codes and standards intended for an LVDC system in buildings.The critical step of developing a DC distribution system is selecting the voltage level. Earlier studies conclude that:•A standard voltage level of 230 V DC is proven to be sufficient for normal office loads, as long as the cable length does not exceed 80 m•For higher power loads up to 6.5 kW the voltage level has to be increased to 326 V DC for systems with a cable length of maximum 47 m and 2.5 mm2This study proposes an LVDC system supplied by converted power from the main grid (AC-DC), where the size of the LVDC system is decided by performed measurements at an example building. In order to compare the losses in an AC and DC system, it was chosen to perform simulations on component level. It can be concluded that:•An LVDC system supplied by a central VSC converting power from the AC grid is an energy efficient system solution compared to the existing AC system solution, largely depending on the performance of the VSCSimulations and calculations resulted in a requirement of performance > 97.7 % of the VSC in order for it to be more energy efficient with an DC system instead of the existing AC system solution with AC-DC converters in each link with a performance of approximately 97 %. Experts believe that it is possible to gain this performance in the future based on performance for smaller converters developed by leading manufactures.Based on the different aspects considered regarding introduction of an LVDC distribution system, simulated models, and performed measurements, it can be concluded that:•From earlier studies it can be concluded that on the economic side, an LVDC distribution system seems benefitual•Original DC loads will benefit from having a separate DC system in terms of power loss at a voltage level of 230 V DC•AC loads require high power delivered and it will be most energy efficient to keep the connection to the existing AC system•An LVDC system with a size of approximate 20 kW is realistic in the future, supplying a floor in a building with DC loadsFrom the material presented in this report, it can be summarised that it is a realistic possibility for future distribution systems in buildings to have an energy efficient mixed supply system, AC and DC.

Particle Swarm Optimization (PSO) and Genetic Algorithms (GA) are usedto reduce the cost of a permanent magnet synchronous generator with concentratedwindings for tidal power applications. Reducing the cost of the electricalmachine is one way of making tidal energy more competitive compared to traditionalsources of electricity.Hybrid optimization combining PSO or GA with gradient based algorithmsseems to be suited for design of electrical machines. Results from optimizationwith Matlab indicate that hybrid GA performs better than Hybrid PSO forthis kind of optimization problems. Hybrid GA shows better convergence, lessvariance and shorter computation time than hybrid PSO.Hybrid GA managed to converge to an average cost of the generator that is 5.2% lower than what was reached by the hybrid PSO. Optimization results showa variance that is 98.6 % lower for hybrid GA than it is for hybrid PSO. Movingfrom a pure GA optimization to the hybrid version reduced the average cost31.2 %.Parallel processing features are able to reduce the computation time of eachoptimization up to 97 % for large problems. The time it took to compute aGA problem with 2500 individuals was reduced from 12 hours to 21 minutesby switching from a single-processor computer to a computer with 48 processorcores. The run time for PSO with 400 particles and 100 iterations went from18.5 hours to 74 minutes, a 93 % reduction.

Smart energy cities have a potential to lead the transition from fossil age into the age of renewables. After a theoretical background is presented, of why the transition is necessary and what steps need to be taken in that direction, this paper brings insight into the paradigm of smart cities. The focus is set on the smart building as its fundamental building block. Fifteen cases of turning Norwegian and Croatian households into smart ones have been analyzed. Those are various combinations of consumption, generation and storage options. Expenses and revenues in case of implementing such smart households are presented by conducted cost and benefit analysis, as well as profitability of such projects.This assignment is realized as a part of the collaborative project "Sustainable Energy and Environment in Western Balkans" that aims to develop and establish five new internationally recognized MSc study programs for the field of "Sustainable Energy and Environment", one at each of the five collaborating universities in three different WB countries. The project is funded through the Norwegian Programme in Higher Education, Research and Development in the Western Balkans, Programme 3: Energy Sector (HERD Energy) for the period 2011 - 2014.

This project was done in cooperation with the TE-EPC-LPC section at CERN. They were experiencing failures in one of their power converter from the rectifying power diodes, and were interested in finding the reason for the failure. They were observing a high leakage current in some of the diodes. The purpose of this project was therefor to investigate the reliability of a diode, and its different failure mechanisms. Diodes can fail from multiple mechanisms some of which can be detected under operation of the diode, in this project the possibility of predicting the lifetime of the diode from its reverse leakage current was investigated. CERN suspected that the failure was either due to avalanche currents in the device or because thermal cycling in the device. Therefor was a non-repetitive avalanche current test, repetitive avalanche current test and a power cycling test performed on the diode. The non- repetitive avalanche current test gave no failures, proving that single event avalanches were not the reason for failure. In the repetitive avalanche current test the diodes was crashed, but no connection between leakage current and time before failure could be observed. In the power cycle test it was observed that failure was induced much faster in a diode with a much higher reverse leakage current than another.

The operational properties of a bipolar configuration composed of a Line-Commutated Converter (LCC) and a Voltage Source Converter (VSC) in a multilevel topology (MMC) are investigated. Simulation models are made in the PSCAD software in order to represent the two bipolar HVDC-links between Norway and Denmark, named Skagerrak 3 and Skagerrak 4. The topology combines two fundamentally different converter technologies with an intricate switching scheme for the function of power reversal.The objective of this thesis is to validate the three simulation models; a monopolar LCC model, a monopolar Modular Multilevel Converter (MMC) model, and an LCC-MMC model in a bipolar configuration. By investigating the interaction of the combined LCC model and MMC model, a better understanding of the challenges of the bipolar link is achieved. The steady state behaviors of the three systems are as expected based on the theory. The LCC consumes reactive power, and require reactive power compensation and filtering. When combined with the MMC, the MMC is able to provide the reactive power consumption by the system. There is an interaction between the MMC and the passive filters of the LCC, resulting in the need to redesign the filters in the bipolar configuration. Also, the DC voltages in the combined model are found to be divided somewhat unevenly between the HVDC-links.When a three-phase to ground fault is applied to the inverter side of the models, the LCC suffer from failure of commutation. This is due to the reduction in the AC voltage, and is to be expected. A DC chopper is placed at the MMC DC-link and reduces the DC voltage overshoot significantly during the fault. When the LCC and MMC systems are combined, they operate in an independent manner, and as a result, no additional protection arrangements are necessary.A single-phase to ground fault at the inverter side of the models, gives rise to harmonic disturbances due to the unbalance of the fault. The reduction in AC voltage results in failure of commutation at the LCC inverter side. The LCC and MMC systems are still almost unaffected by each other during the fault, and so no additional protection systems are required for the combined model.Finally, a DC pole to ground fault is applied to the three simulation models. The LCC model does not recover from the fault, because of loss of controllability in the PI controllers. There are solutions for this problem, for example anti-windup PI controller. An interesting result is observed when the two models are combined into the bipolar configuration. The MMC is able to support the LCC in such a way that it recovers. DC breakers are required for high voltage and current spikes during the DC fault at the MMC link. The LCC and MMC systems are no longer operating independently, and different protection strategies must be implemented when compared to the monopolar models.