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During the past years, wind turbine technology has improved and the demand for new installations is increasing. The transmission system operators have looked into different technologies. Three technologies are discussed in this Masters thesis. The first is the simple induction generator, which is one of the oldest technologies, but is becoming installed less because of increasing requirements of grid codes in Europe. Doubly fed induction generator (DFIG) technology is also examined, and the impact of two features, the crowbar and the chopper. Lastly direct drive synchronous generator (DDSG) technology is discussed. The disconnection of wind farms due to fault in the western part of France is examined. The volume of shed wind power is highly dependent on the voltage level at which the fault occurs. The higher the voltage, the more wind farms are shed. The topology of the grid is also an important factor with regard to wind power shedding. A study has been performed on the fault behaviour of a large DFIG wind farm installed near some nuclear power plants. If the fault occurs near these generating units, the wind farms will affect the stability of the power system, and the critical clearing time will decrease. The installation of active power regulation in the wind farms can reduce this effect.

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Access to electricity is a key factor of improving the living standard in a country, as it enhances the quality of services such as education, health care and productivity. The rural population of Uganda is however only supplied with electricity to a degree less than three percent. There are large financial issues in extending the national electricity grid why small stand alone systems are sometimes a more valuable option. Even then, there are large investment costs that need to be covered by the sale of electricity. Due to the limited buying power of rural consumers, the end-user tariff setting becomes of great significance of the financial outlook. If the tariff is set too high, the consumption will most likely be lower than what it could be, resulting in a loss of revenue as well as inhibiting the improvement of living standards for the consumers. On the other hand, if the tariff is set too low, it could lead to excessive consumption, resulting in power failures. In view of the above, the main aim of this study has been to investigate the consequences of different tariffs in an isolated rural power system. This was done by studying the electricity consumption in two already electrified rural networks in order to find information on demand behavior and load profiles. Interviews with electricity consumers were conducted to investigate how their demand would change if tariffs were altered. Demand as a function of price was shown by linear curves indicating the price sensitivity and demand factor, the latter being the theoretical maximum demand when price is zero. These parameters were modelled in Monte Carlo simulations with the aim to predict the demand behavior of a site that is not yet electrified and find the tariff that should be applied to this site. The simulations were based on two potential economic objectives of how to operate the system; by altruistic or profit maximising means. Depending on whether the system is altruistic or profit maximizing, the optimum point of tariff differs. In the altruistic case, this tariff should be set where the costs are covered by the revenues. The profit maximizing system instead requests the tariff where profit is as high as possible. Furthermore, two different structures of tariff setting were tested for the system; a structure with time-of-use levels where the tariff should be higher during the peak demand hours of the day, and a flat rate structure where the tariff is constant throughout the day. The field study showed that, on average, the price sensitivity factor of domestic consumers were slightly higher than of the commercial consumers. The results also showed that the majority of the commercial consumers reside in the same building as their business. Furthermore, rural consumers exhibit low awareness of their consumption patterns and the price of electricity. Extensive information from the distribution companies to the customers is therefore essential to maintain a sustainable electricity consumption, as it enables consumers to make rational decisions about their electricity consumption and opt for more efficient alternatives. A financial analysis for the specific case study was also conducted from simulations. The analysis found for an altruistic system a tariff slighly lower tariff than the tariff applied in the national grid today. However, the system will require an additional financing to cover the payments before the year when revenues exceed expenses, but can be paid back within eight years. The tariffs found by simulating with a profit maximizing system operator are more than twice as high as the current tariff applied in the national grid today. On the other hand, the system requires a very small additional loan or subsidy compared to the altruistic simulations and has a pay-off time within six years.

Numerical simulations play a vital role in both static and dynamic stability assessment of electric power systems and the foreseeing of voltage collapse. Simulations performed by Svenska Kraftnät (SvK) are mainly done in the specialized voltage collapse predicting software tool, SPICA and the more all‐purpose software tool, ARISTO. The grid operators at SvK use SPICA to predict the maximum transfer limit at specified sections (in this report the section in concerns is the southern part of Sweden i.e. interface1 4). SPICA is mainly used as an online application by using actual states from the grid, these states update every quarter of an hour. This thesis is a continuation of the master thesis SPICA – ARISTO JÄMFÖRELSE by Jakob Katzman and Johan Fält. Royal Institute of Technology, Stockholm, May 2004. The task in this thesis is to seek alternative applied methods that can enhance the existing methodologies that are used by SPICA and ARISTO, to make the power system more efficient and reliable. The alternative methods involve alternative load modeling, voltage control capability of the sub‐transmission network and its impact on voltage stability and changing of SPICA parameters. Investigation was done in SPICA and the results were later validated in ARISTO. As it will show in this thesis the different load characteristics did not have an impact in SPICA due to SPICA’s Load Tap Changer model which keeps the voltage at the sub‐transmission level constant. On the other hand due to different load models and ARISTO’s time delay dynamic model ability, a lot of dynamic phenomena were presented in the ARSTIO simulations, phenomena like rotor angle instability. It is also shown that a voltage insensitive load model for both the reactive and active load power is not a recommended load alteration in ARISTO. An analysis is made to enhance SPICA calculations by tuning the programs parameters and later validate the results in ARISTO. The results show that by changing some parameters, divergence in SPICA calculations, which is a huge problem for grid operators, can be avoided. Also the load model has a role in SPICA’s ability not to diverge from a solution. Other parameters that had an impact on the SPICA calculations were where the geographical positioning of the continually increasing loads. Export to other countries is a common operation. This thesis has studied transmission capacity when only the export is increased. The results differ between SPICA and ARISTO. In SPICA the transmission ability to other systems remains basically the same as for load increase in company 4 for intact grid albeit when the grid is weakened2 there is quite a difference between the two increasing methods. Note that the results are independent of the load model. Where as in ARISTO if only the export is 1 The word ”interface” is used as the English translation of ”snitt” which is a term used to describe a set of transmission lines (or transformers) that carry the main power transfer between two areas, thus, snitt 4 is translated to interface 4. Also, the area between two interfaces is called “company” which is the English translation of “snittområde”. 2 A grid fault that has the most impact on the transmission capacity is applied to the system. increased then the system has an increased transmission capacity compared to if the loads are onlyincreased in company 4 independent of the condition of the grid, the transmission capacity differswith the load model. Note that neither of the tools have a complete DC‐link model or transmissionsystem model for the neighboring countries. During the simulations, weak system buses could be identified at the south‐west part of Sweden, this comes as no surprise to the people at SvK. Other conclusions that are presented are the actual operator process when using a SPICA calculated limit. It is important that the operator is aware of the reactive state of the system, that is, how much reactive power reserve in the form of not activated reactors, condensers, generators and other voltage regulator devices there are in the system. If there are a lot of reserves left then one has to be very careful of the transmission limit predictions made by SPICA calculations.

This master thesis project aims at improving a train power system program which simulates the interaction between a predefined train power supply system structure and a train traffic schedule. The simulator, called TPSS (Train Power System Simulator), is used for training TPSA (Train Power System Approximator) which is included in a larger investment planning program where the welfare of the society is to be maximized. The development of the railway power system implies wise investments that should last a long time. In order to make the good decisions, the consequences of different power system configurations related to the future train traffic demands have to be studied. Aiming at an investment planning in the long term, models and methods used by the simulator for the railway power system and the electric traction devices are of great importance. In this thesis electrical and mechanical models are presented and improvements are discussed thereafter. Moreover methods were modified to improve the accuracy and reduce the simulator running time. Indeed reduction of the computation time is really important when a great variety of cases are studied. In addition some further controls are implemented to obtain more workable and more realistic outcomes. Some bugs are fixed and the former models are changed aiming at a faster computation time and a better quality of the results. Comparisons between the different simulator versions are presented along the report to illustrate the benefits of the changes. Finally a global examination showing impacts of all improvements is performed. As explained the program TPSS intends to participate in a long term investment planning suggestion. The program.s outcomes of several simulations would be extracted to train a Neural Network. The latter will aim at approximating outcomes for other cases avoiding too many simulations and thus saving time.

In this thesis an investigation of voltage stability improvement for power systems with VSCHVDC has been demonstrated. This investigation has been made by controlling active power flow through VSC-HVDC. The present work is demonstrated by comparing the VSC-HVDC to decrease and increase of active power transmission through VSC-HVDC, where VSCHVDC is one such device that can be used to quickly supply reactive power if the voltage goes below a certain level.

Questions raised on the basis of this work are, witch loads are there at the stations, how big are the loads, are there nonlinear loads, are there motor loads with high starting currents, how do the rectifiers interact with batteries? The diesel unit starts about 10 minutes after a regional or national interference in a transformer station. The station’s DC power system is then fed during that time from batteries. The question of how rectifiers interact with the batteries is of importance because rectifiers are large instantaneous loads after some discharge of the battery. The loads that occur at the stations is heat in the control building, server room cooling, lighting inside and out, cooling the reactor, electrical engines, PTO, heating for high voltage circuit breakers etc. These loads will not be active simultaneously and each will not consume a maximum power all the time. This means that you must find the tools to handle these loads. The present report presents developed load factor of the various components involved. A diesel generator model has been developed consisting of a diesel engine coupled to a synchronous generator in operation through two control systems to regulate voltage and rotor speed. Based on measurements at stations with diesel power, steering systems have been modified for the unit to conform to reality as much as possible. Based on the model, simulations have been done to see what the start-up currents from the motor loads have for effect of voltage and frequency with different sizes of diesel generators. Calculations have been made to examine the size of short circuit currents in different levels of the station's electrical system. This is to analyse if the fuses can be broken if necessary. Duration curves of station loads are presented from various measurements to get a better picture of how the total load actually behaves. From there, appropriate diesel unit size is developed and also EENS and LOLP are calculated. Duration curves are also simulated based on the load factors that have been worked out and the actual duration curves made. The idea is that the simulated duration curve should conform to reality for engineers to be able to examine the probability of power shortages in emergency use in a planned station. The results of the report are guidelines and instructions for an easy way to make good diesel units dimensioning of a reserve and emergency operation. It turned out that the rectifiers have to be started in sequence to avoid to large fast charge cycles. Also a safety factor is multiplied to the rectifier continuous operation to avoid harmonics in the system at emergency operations. Start currents from reactors cooling system must be analyzed separately and the generator requirements for those is determined from calculations found in the guide. It also turned out to a certain station can get by with a diesel unit at 100kVA instead of the current 400kVA.

This thesis analyzes the generator loss of excitation fault and describes an investigation on existing loss of excitation protection schemes. In addition, a simulation model is established in PSCAD to simulate the loss of excitation fault and external faults. According to the simulation results, this thesis compares the speed of different protection schemes on loss of excitation fault detection and finds the drawbacks of some protection schemes on fault detection during special operation condition. What’s more, this thesis also compares the stabilities of different loss of excitation protection schemes during generator external faults. Finally, this thesis summarizes the advantages and disadvantages of different schemes and serves as a reference for selecting the loss of excitation protection scheme.

As the mobility of people increases, so does the density of vehicles on road networks. This comes at a cost, causing traffic congestions and raising the number of casualties. Wire- less communications  between vehicles will enable the development of Intelligent Transport Systems (ITS), which are expected to assist and manage road transportation.  The aim of  ITS is to enhance safety, road network management,  but also personal comfort for drivers and passengers.   IEEE 802.11p has been chosen  as the standard for the Physi- cal Layer (PHY)  design for wireless vehicular communications. Unfortunately, vehicular channels are challenging for communications. While the dispersive nature of the channel has  advantages, such as the possibility to communicate in the absence of line-of-sight, time variations present in high mobility scenarios lead to doubly selective channels. The systems are expected to allow reliable communications despite those conditions. In this thesis we focus on PHY  design for the receiver.  We  aim at implementing receivers  able to perform channel estimation in the case  of doubly selective  channels, with minimal information from training sequences.  The solutions considered all involve joint channel estimation and decoding, characterized by the use of an iterative structure. As limited knowledge of the channel is available at the receiver, only a coarse estimate can be performed in the first place. Iterative structures allow the channel estimator to benefit from feedback produced by the decoder, used to refine the channel estimation and ultimately  resulting in a smaller error rate.  Different  algorithms are considered, either based on Minimum Mean Square Estimation (MMSE), or Maximum A Posteriori (MAP)  estimation.   The latter  requires a recursive description of the channel introduced as a Markov chain.  Using these powerful methods to perform channel estimation, we decrease the error rate, despite the varying nature of the channel. However, improving the channel estimation comes at the cost of a higher complexity. An analysis on the trade-off between performance and complexity is also provided.