One of the world’s largest energy user is the building sector, where much of the energy goes to cooling of buildings. There is need for novel technology to reduce this energy usage, and one way is to install electrochromic windows. They have the ability to vary the transmittance of visible and infrared light by the application of a small electrical voltage, and hence to save large amounts of energy and money and to increase indoor comfort by avoiding strong glares from sunlight. This study concentrates on thin-film electrochromic devices that are based on flexible polyester foils. The conventional design is to make rectangular devices with contacts placed on transparent conductor layers opposite of each other. An electric potential is applied between the contacts, generating an electric field which causes ions to move between films of electrochromic active materials. Since there is an interest on the market for electrochromic windows of other geometries, such as triangular, there is a need to know how to place the contacts in order to obtain a rapid and uniform colouring and bleaching of the device. In order to investigate this, a mathematical model describing the current distribution over the device is a great tool. The model used in this study takes secondary current distribution into account, which includes ohmic effects and electrode kinetics, but neglects diffusive effects due to the assumption that the electrolyte is homogeneous. It describes the two dimensional ohmic flow through the transparent conductor films, the local current due to electrochemical effects in the electrochromic active materials, and a correlation between the optical properties and the injected charge over time. The model is simulated using FlexPDE, which solves the system of differential equations using a Finite Elements Method (FEM). To adjust model parameters, model simulation results are compared to experimental data from rectangular electrochromic devices. Initially, experiments are done on small are devices on which current distribution effects are small. The model is then further developed and validated using large area rectangular devices with 67 cm between the contacts. The model is shown to meet the aims of this study, which is to obtain a simulation tool which can predict the trend in the transmittance distribution. The strength of having this model at hands is that it becomes possible to simulate the transmittance behaviour over time for full size electrochromic windows of different geometries, without having to manufacture expensive devices for experiments. It provides a great design tool for optimizing a rapid and uniform colouring and bleaching, and to investigate how to reduce material costs without affecting performance too much. In this study an example which shows the strength of the model is given. The placement of contacts and its effect on the transmittance distribution in triangular electrochromic windows is examined. It shows that the current distribution model enables time-efficient and cheap design of electrochromic windows.

Lightning constitutes a serious threat to the electrical grid. If not protected against, lightning can cause comprehensive damage, harm to humans and lead to disruption in the electricity supply. Modeling of lightning protection is hence an important part of operating the grid. The amplitude of the lightning current is a decisive factor in the induced overvoltage in electrical systems. Knowledge about which peak current amplitudes one can expect in a lightning event, and how often such events occur, form the basis in modeling and evaluating the lightning protection system. Today, the Swedish authority Svenska kraftnät models the lightning protection system based on current distributions recommended by CIGRE. The aim of this thesis is to examine lightning data gathered by the Swedish lightning location system (LLS), owned, and operated by the Swedish Meteorological and Hydrological Institute (SMHI), to derive statistical distributions for the lightning peak current. This is done at a national and a regional level for the years 2006-2020, the focus being on the period 2015-2020. The results are then compared with the distributions recommended by CIGRE, to evaluate whether the protection levels used today are justified. Lightning is a complex phenomenon whose properties need to be understood to measure its features and interpret the measurement results. Similarly, the quality and the shortcomings of the LLS must be addressed and considered when analyzing the results. The peak current estimation done by the LLS tends to be an underestimate, as the system is only validated for the subsequent strokes of negative lightning. Nevertheless, the LLS offers a large data set which, while individual measurements are not fully accurate, provides a representative statistical distribution exhibiting the tendencies of lightning peak current amplitude. The results show that the current distribution fits a lognormal and generalized extreme value distribution, the latter yielding a slightly better representation. A small regional variation in median peak current is seen, where somewhat higher amplitudes are found in Northern rather than Southern Sweden. The national analysis shows a significantly lower median peak current in Sweden compared to the reference median peak current recommended by CIGRE. Calibration of the LLS can be assigned a portion of this difference, the remaining is thought to represent a difference in lightning peak current. Unfortunately, there is no reliable way of knowing how large the calibration error is without further studies comparing data from the LLS with direct measurements. Consequently, deviating Swedish lightning conditions cannot be stated, although tendencies towards lower peak current amplitudes are seen.

Med behovet på allt större transformatorer på hög- och mellanspänningsnivå krävs i mångafall flera parallella kablar på nedsida transformator, ibland ända upp till 6 parallella förband. Detta ställer särskilda krav på förläggning av förbanden för att undvika ojämn strömfördelning i ledarna. Karlstad Kraftteknik har observerat flera stationer med stora problem att upprätthålla en jämn strömfördelning i ledarna mellan samma faser. Detta beror delvis på att kabelschakten är breda och har svängar, vilket skapar skillnader i längd mellan inner- och ytterförbanden, men även där förläggningen i triangel är viktig att hålla så långt som möjligt. Syftet med examensarbetet var att fokusera på hur flera parallella triangelförband förläggas för att minska ojämn strömfördelning, och vilka metoder som krävs för att säkerhetsställa en jämn strömfördelning innan ställverket är redo för spänningssättning. Tillvägagångssättet har varit att analysera hur olika förläggningsmetoder påverkar strömfördelning. Genom mätningar, utförda tester, simuleringar och fördjupad litteraturstudier. Rapporten resulterade i att det är viktigt att förlägga de parallella kabelförbanden med lika längd, eftersom längden har en stor påverkan på strömfördelningen inom korta ledningar. Det är även viktigt att ta hänsyn till avståndet mellan de parallella förbanden, då ökat avstånd mellan förbanden kan öka självinduktansen och påverka impedansen i kablarna. Förbanden bör även läggas med så lika och jämnt avstånd som möjligt för att undvika olikheter i magnetiska flödestätheten som kan orsaka ojämn fördelning mellan de parallella ledarna.