The grid in the northern part of Sweden is characterized by long radial lines with just a few customers. To secure electricity supply it is necessary to have a redundant feeding alternative. A loop structured grid which is used in the more populated urban area is a poor solution in the rural areas both regarding economy and technology due to the long distances. To feed the northern grid in Sweden a battery energy storage system (BESS) is therefore a solution that could secure the power delivery. An important aspect to investigate is how the electric power quality changes with the new feeder, but more importantly to secure disconnection of supply at fault occurrence.   This thesis investigates how a battery storage system installed at the end of a mid-voltage line affects the electric power quality and the protection system compared to a reference case which represents the line today. The mid-voltage line is an existing line in the northern grid and is a good representation of the general northern grid.     The results obtained from this study show that the loop impedance does not necessarily have to deteriorate with the new feeder, which means that the voltage quality in this aspect does not change. This is only true for this particular grid when the impedance contribution from the mid-voltage grid is small and the contribution from the low-voltage grid is large because of long and weak distribution low-voltage lines.     The inverter is the limiting factor for the short circuit currents, and the short circuit power and current decrease with the new feeder. At fault occurrence in the low voltage grid the short circuit current does not affect the fuse blow. However the inverter will disconnect for all fault occurrences in the mid-voltage grid, and for faults with high short circuit power in the low voltage grid. This means that the selectivity will decrease, but the system will have a high security level.   For this particular grid the results show that the transformer can be isolated from the ground. A residual overvoltage relay is enough for disconnection of grounding faults. Directional ground fault protection is not necessary for this line with this particular characteristics. If the sensitivity for the disconnection of grounding faults with high transition impedances is adjusted according to ground fault currents in island operation, the sensitivity then decreases at the event of a fault during normal operations when the battery storage system is charging. The sensitivity might also be tuned according to normal operation, which then results in a higher sensitivity than necessary during island operation.

Den här rapporten utreder förutsättningarna för att konstruera om ett mindre distributionsnät på 10 kV i Stockholms skärgård till ett så kallat smart nät med självläkande funktion. Nätet är avlägset och har haft många fel de senaste åren, därför är det önskvärt att kunna lokalisera fel i nätet och automatiskt koppla om till rundmatning direkt ifrån driftcentralen för att minska avbrottstiden för de boende på öarna. Rapporten fokuserar speciellt på att utreda lämpligheten med att använda feldetekteringsutrustningen SICAM FCM i nätet och hur dessa bör ställas in. Information om det aktuella nätet och problemet beskrivs tillsammans med en teoretisk bakgrund. Resultat ifrån tester och felsimuleringar på SICAM FCM med fokus på känslighet kring tröskelvärden presenteras och analyseras. Utifrån testresultat och information om nätet har rekommenderade inställningar för SICAM FCM tillsammans med andra rekommendationer för implementeringen av det självläkande nätet tagits fram. / This report has investigated the conditions for reconstructing a small 10 kV distribution grid in the Stockholm archipelago into a so called smart grid with a self-healing function. The grid is in a remote location and have had a lot of faults during the last years, therefore it is desirable to be able to locate the fault and automatically section it and restore service through a back-up feeder (if needed) to reduce downtime for customers. This report focuses especially on the suitability to use the fault detection equipment SICAM FCM in the grid and to propose how it should be configured. Information about the grid and problem is described together with a theoretical background. The results from tests and fault simulations on the SICAM FCM focused on sensibility around threshold values is presented and analysed. From test results and information about the grid recommended settings for SICAM FCM together with other recommendations for implementation of the self-healing grid has been produced.

The Swedish energy power system is in the middle of a paradigm shift where the increased share of intermittent energy sources place higher demand on the ability to regulate and balance the generation and consumption of electricity. Demand flexibility, which means that consumers can adjust their energy consumption, is a promising solution to manage the imbalance in the power system. Electric heat pumps in residential buildings are recognized to have potential to serve as a flexible load. In this thesis, an aggregated multi-family residential building model is developed to generate heat load profiles for a larger number of buildings which facilitate an assessment of the heat pump flexibility. The flexibility assessment is performed for a local distribution grid area with 174 buildings and an electricity price region in Sweden with 10 146 buildings with heat pumps. The flexibility assessment analyses the heat pump load deviation between a base load case and a case where the heat pumps receive an off-signal. The assessment takes into consideration seven flexibility parameters and is conducted for ambient temperatures between -20°C and 15°C. The thermal inertia of multi-family residential buildings facilitates a load shift with a duration of 4.4 to 9.8 hours depending on the ambient temperature. The maximal average power reduction for one hour of 10 MW in a distribution grid and 169 MW in an electricity price region illustrates the potential of using heat pumps as a demand flexibility solution in the electricity grid.

The Paris Agreement was formed in 2015 to reduce the environmental impact and limit the increase in temperature to 2°C compared to pre-industrial levels. It is believed that an electrification of the transport sector will reduce its negative environmental impact. To reach the goals set by the Paris Agreement we are in need of quick development towards an electrified fleet of vehicles. Despite this urgency electric vehicles (EVs) have failed to reach the majority of the market, instead it has stuck in the chasm between the early adopters and the early majority of the markets. This is due to three main challenges; EVs are relatively expensive compared to conventional petrol- and diesel-powered vehicles, EVs have an inadequate driving range, and the access to a functional charging infrastructure is limited. This thesis focuses on the third challenge regarding charging infrastructure. The charging infrastructure is dependent on the existing electricity distribution infrastructure, i.e. the grid. It is rather time-consuming and costly to strengthen the grid, which is deemed necessary for enabling a roll-out of a charging infrastructure that meets the needs of current and near-future EV operators. This research provides an alternative way of approaching the issues. Instead of strengthening the grid by digging up old cables it looks into the opportunities of incorporating stationary battery storages as a buffer between the EV charging stations and the grid connection point. This battery solution can reduce the power outtake and smoothen out the load from EV charging, thus limiting the impact of EV charging from a grid perspective. The research assesses what type of pathways this solution could follow to successfully drive the adoption of EVs. Furthermore, the study tries to understand how these solutions could be designed to deliver the necessary values regarding EV charging and reducing the overall power outtake from grid connection points. The thesis is carried out by analyzing collected quantitative and qualitative data through the lens of three main theories. These are transition theory, theory on eco-innovations, and theory on the diffusion of innovations. The thesis finds that the two pathways for a battery supported charging infrastructure that will be most efficient in speeding up the adoption rate of EVs is within a workplace and public charging setting in city and urban environments. For both pathways it is expected that a centralized concept, with one battery solution connected to several charging points, will be most feasible in the short-term, which is important as the need for developments are very urgent. The workplace charging will provide 3,6 kW AC-charging while the public charging provides 150 kW DC-charging. The solution is expected to be cost-efficient for specific locations, especially for public charging in city environments with strained grid infrastructures. The study provides an initial assessment for the city of Stockholm which indicates that the power outtake can be reduced by 63,5–112,2 MW in 2030. This means that the current grid infrastructure could support a larger number of EVs, thus reducing the greenhouse-gas emissions from the transport sector and bringing us closer to reaching the goals set by the Paris Agreement. / Parisavtalet utformades år 2015 för att reducera vår klimatpåverkan och begränsa temperaturökningen till 2°C jämfört med nivåerna som rådde innan den industriella revolutionen. Förhoppningen är att en elektrifiering av transportsektorn kan reducera dess negativa klimatpåverkan. För att nå målen i Parisavtalet behövs en snabb omställning mot en elektrifiering av fordonsflottan. Trots situationens brådskande karaktär har elbilar fastnat i en klyfta mellan den begränsade tidiga marknaden och den sena marknaden, vilken utgör majoriteten av kunderna. Det finns tre primära anledningar till detta; elbilar är dyra jämfört med bensin- och dieseldrivna bilar, räckvidden för elbilar är otillräcklig, och det råder begränsad tillgång till en funktionell laddinfrastruktur. Den här studien fokuserar på den tredje anledningen kring otillräcklig laddinfrastruktur. Laddinfrastrukturen är beroende av det existerande elnätet och dess distributionskapacitet. En förstärkning av elnätet är i många fall nödvändig för att möjliggöra en utrullning av en laddinfrastruktur som möter dagens och morgondagens behov. Istället för att förstärka elnätet genom att gräva ner tjockare kablar så fokuserar denna studie på en alternativ lösning kring laddinfrastruktur sammankopplat med stationära batterilager. Batterilagret agerar som en buffert mellan anslutningspunkten till elnätet och laddningspunkten för elbilar. Genom att reducera effektuttaget och jämna ut lastkurvan för elbilsladdning kan en batterilösning begränsa den negativa påverkan det förväntas ha på elnätet. Studien undersöker vilka vägar denna batterilösning kan ta för att öka antalet elbilar i fordonsflottan. Efter att ha förstått vilka dessa lösningsvägar är så analyserar studien hur dessa lösningar kan vara uppbyggda för att erbjuda de efterfrågade och nödvändiga värdena för elbilsladdning och elnätets fortsatta funktionalitet. Studien bygger på analys av kvalitativa och kvantitativa data. Analysen utförs genom att applicera koncept hämtade från teorier kring teknologiska övergångar, miljöinnovationer och spridning av innovationer. De två lösningsområden som förväntas vara mest effektiva i att driva en ökning av antalet elbilar i Sverige är arbetsplatsladdning samt offentlig laddning i stadsmiljöer. En lösning med ett centraliserat batterisystem där en batterilösning är kopplat till flera laddstationer antas vara mest genomförbar på kort sikt, vilket anses vara centralt på grund av utmaningarnas brådskande karaktär. För arbetsplatsladdning tillhandahålls 3,6 kW AC-laddning och för offentlig laddning tillhandahålls 150 kW DC-laddning. Lösningarna förväntas vara kostnadseffektiva for specifika platser och användarprofiler, speciellt för offentlig laddning i stadsområden med ansträngda elnät. En initial uppskattning visar att en laddinfrastruktur kopplat till stationära batterilager inom de två lösningsområdena kan minska Stockholms effektuttag för elbilsladdning med 63,5–112,2 MW år 2030. Detta betyder att dagens elnät kan tillgodose ett ökat antal elbilar, vilka genererar färre utsläpp av växthusgaser och ger oss en bättre chans att nå Parisavtalets mål.