Examensarbeten på grundnivå // Basic Level Theses
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- PostCell characterization and modeling of lithium ion batteries(2016) Strängberg, Victor; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe purpose with this thesis was to estimate the parameters from one of the electrical equivalent circuits that are used for batteries. Two different batteries with different chemistries have been tested. First measurements at different frequencies have been performed to obtain the impedance at a specific frequency. When the impedance is known, the information can be used in a Nyquist diagram, where two parameters can be estimated, then the rest of the parameters are calculated from transfer functions. Two methods have been tested to achieve the parameter values. This thesis has tested two batteries at different State of charge and temperatures. The State of charge have been tested from either 0 - 100 % or 100 - 0 % State of charge and the temperatures have been tested between 0° C and 40° C.
- PostDistribuerad genererings påverkan på dimensionering och planering av lågspänningsnätet i Halmstad(2016) Tahir, Soran; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentA study about how micro production from photovoltaic cells affects a low voltage network was conducted at Halmstad Energi och Miljö Nät AB, where a fictive residential area working as a test network was built up in the programme dpPower with help of theory collection and the knowledge of planning and power engineers at Halmstad Energi och Miljö Nät AB. The fictive network was divided into two areas, each with its own secondary substation, one with 41 loads and the other with 171 loads in form of detached houses/ town houses, kindergarten / schools and blocks of flats. Studies on the fictive network were done when the loads had minimum power consumption and the power from the micro production of detached houses/ town houses varied in the ranges 8 kW, 20 kW, 32 kW, 43, 5 kW, whereas kindergarten/schools and blocks of flats had constant micro production. The result showed, as the share of micro production and the power of micro production was increasing the number of loads with overvoltage in the recommended level (5 % of the nominal phase voltage) and critical level (10 % of the nominal phase voltage) where increasing. The transformers’ rated power are exceeded when micro production power in each detached house/ town house was 8,5 kW in the larger area and 20 kW at the smaller area, in the case when every load had micro production connected.In planned residential areas with a high potential of micro production, the numbers of loads connected to the substation should be considered compared to areas without micro production. The number of loads connected to the substation compartment should be considered in order to prevent over voltages at the cable cabinets and at loads. The thesis is concluded with a recommendation on numbers of loads connected to the substation compartment at the different micro production levels.
- PostElkvalitet på Ringhals(2015) Carlund, Olof; Johansson, Johannes; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentDue to upcoming modernization projects, Ringhals desires an estimation of the current power quality in their local power supply. The purpose of this thesis is to initially, clearly describe, the meaning of the term power quality and what it is that might affect it. As part of the basis for the analysis part of this project lays existing measurement data from an earlier project within Ringhals. There is also an additional measurement carried out within this project of a potential source of harmonics, the thyristor rectifier. This project focuses on phenomena in form of voltage dips, transients and harmonics. When analyzed during normal operation there is no sign of notable levels of either of these phenomena with one exception for the measurement at the 21.5 kV-level, where there is a clearly visible third harmonic, approximately 3.65 %. However, it is isolated to this level in the plant due to the delta coupling of the transformers and the source is probably the main generator. In addition, the loads are connected between phases, so this means they are unaffected by the 3rd harmonic. When measuring the thyristor rectifier the magnitude of the fifth harmonic increased with the load, but due to limited loading options it was not possible to investigate it further. When analyzing data from triggered events, there was a distinct voltage dip at all measured levels in the plant due to a lightning event in the national 400 kV transmission grid at some distance from the plant. At the lowest mark the remaining phase voltage was approximately 67 %, this at the 400 kV-level, which is just under the limit that the plant shall be able to handle momentarily (70 %). The voltage dip is reduced a bit when propagating downwards in the plant and at the lowest point of measuring; the remaining phase voltage is about 76 %. The measurements also showed a heavy motor start and compared to the calculations done in the hypothesis, the voltage dip obtained through theory matches the measured values, 15.7 % respectively 15 %. The main conclusion of this thesis is that Ringhals local power supply is very solid and the only time during this project that there was anything close to a problem, was the voltage dip due to the lightning event.
- PostMätning av egenskaper hos elmotor och transformatorplåt(2013) Bajra, Mernis; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentCore loss measurements have been done. Because of the low magnetization current of the toroid the current was measured with a current transducer of model LA 100-S/SP1 and the voltage was measured with a voltage probe of model TT-SI9101 for better accuracy. The knowledge of the current and voltage made it possible to calculate the magnetic field strength and the magnetic field density and further with that the core losses. The obtained losses did not match with the losses given by the datasheet. The reason for the mismatch can be that the dimensions of the toroid core contribute in measuring the B-field value wrong.
- PostOmriktare för solceller med energilager(2017) Olofsson, Simon; Johansson, Markus; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentBox of Energy is a company in Gothenburg who offers battery storage in connection to both solar energy and wind energy and direct connection to the electric grid. They are working to raise the output power that their battery storage can deliver. One way to solve that is to find a new inverter. The company have also received a project to calculate how much battery storage is needed for a row of garages in a residential area where plug-in hybrid and electric cars will be charging. The purpose of this essay has been to find a new inverter for Box of Energy. This, so the company would be able to increase the output power of their battery storage. A market research was made by going to different inverter manufactures homepages and go through their datasheets for the inverters they offered. The project then went on to compare different providers of battery storages on the market. This was also done by visiting their homepages and going through datasheets. Then, lastly, calculation of the charging power for hybrid and electrical cars in a residential area was carried out. The area consisted of 150 houses and rows of garages with 16 garages on each row. The charging of the cars is assumed to happen simultaneously and that leads to very high load on the electric grid. By installing battery storage between the electric grid and the cars the load will be lower. Through the market research it was established that there is a big range of different inverters. They vary in both capacity and physical size. The inverter that was considered the most interesting one was SG10KTL-EC and is delivered by Sungrow power. When it comes to the residential area it could be established that the amount of battery storage was linked to the charging power that the cars demanded. If the garages only contained electric cars and not plug-in hybrids the load would be the highest and demand the biggest amount of battery storage units. At the same time, it could be established that the effect of not using any battery storage would lead to the need of changing the fuse since the original one would be too low. It would also be needed to install new cables. Should, on the other hand, a currently theoretical software be implemented that can distribute the charging of the cars evenly during the night, the load becomes significantly smaller and then battery storage would not be a necessary solution.
- PostStröm- och spänningsripplets påverkan på DC-ledet i ett elfordon. Verifikation av teoretiska resultat genom mätningar.(2015) Enqvist, Mikael; Hellberg, Emil; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThis thesis work examines the current and voltage ripple present in the DC link when an induction machine is powered by a battery source through a three phase inverter. The project evaluates the ripple at different frequencies that is generated due to the combined working principles of the induction machine and the switching of the inverter transistor. An available electrochemical impedance spectroscopy measurement of one battery cell identical to the type used in this project is used in a computer model to simulate and verify the ripple components against the measurement results from the physical model. The measurements show that sigificant levels of ripple in DC link voltage and current are present. Frequency analyses of the resulting waveforms show that the sixth harmonic component as well as multiples of the inverter switching frequency and their sidebands dominate the ripple waveforms. Simulations of DC link voltage and current ripple show that the characteristics and magnitude of the measured ripple components can be verified, however, with some deviation. A possible cause for deviation is due to the fact that some unknown impedances present in the physical battery system could not be measured and therefore are not represented in the computer model.
- PostUtredning av hållbar elnätstruktur för tät blandstad(2016) Lind, Philip; Malmqvist, Joakim; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentWhen building a new area in a modern dense city with a mix of residential and commercial buildings, it can be difficult to use the traditional type of distribution grid with a large part of low voltage level for various reasons. The main purpose is therefore to investigate under what circumstances it is more beneficial to build the power grid with mainly medium voltage level and built-in substations instead of external substations. The investigation is being done considering the distribution grid of Göteborg Energi and investigates the possibilities of building medium voltage level regarding some given variables such as cable length, transformer size and load density, i.e. power per area. The characteristics which are being investigated are reliability, space efficiency, environmental impact, cost of investment, operation and maintenance and also losses. Calculations are made based on three different distribution alternatives, low voltage, medium voltage loop distribution and medium voltage radial distribution. To perform the calculations and comparisons a model has been created which calculates the combinations of the given variables. Distribution with mainly medium voltage level gives less losses, takes up less space and causes less CO2 emissions. It also has better reliability than low voltage, especially the case with loop distribution. The built-in substations have a downside of having a big cost to reduce the electromagnetic field exposure, this extra cost can make this alternative more expensive. There may also be an additional cost for obtaining the rights to place lines. What determines the best distribution alternative, besides the cost, is how difficult it is to find places for external substations and extensive placement of low voltage cables. Therefore, it is hard to give an exact answer to at what load density the built-in substations are better, because a certain figure on load density may refer to higher buildings, but still with enough space in between them for external substations, or it can refer to lower buildings with tighter placement where there is no room for external substations.
- PostUtveckling av mätsystem för termisk studie av transformator(2013) Johnsson Hjort, Marcus; Örnberg, Erik; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentThe main limiting factor with respect to continuous power handling in electrical machines and transformers is the temperature rise in the windings. Thermal models are therefore a valuable tool in the design process to be able to predict the operational temperature at certain operating points. To be able to construct such models, an accurate measurement system is needed to obtain the temperature in several positions over the test object. This report describes the construction, calibration and evaluation of such a system. The system has eight channels where each channel is made up by of resistance thermometers, wheatstone bridges with amplification and separate data handling process. All testing are done on an ETD ferrite core with only one winding connected to a DC voltage supply. As a part of the objective of this report, the results from the measurements shall then be analysed to obtain thermal properties for the test object. Regarding accuracy, the system performs well and the temperatures registered can be trusted. Due to very similar temperature levels in windings, they can be modelled as one part. The most important thermal resistance is between the surface of the object to the ambient air. A simple model is then constructed and tested.
- PostVerifiering av mätsystem i 132 kV matarledningssystem för Trafikverket - En undersökning av effektstyrning och dess energibesparing(2017) Bierich, Carl; Magnusson, Emil; Chalmers tekniska högskola / Institutionen för energi och miljö; Chalmers University of Technology / Department of Energy and EnvironmentEtt nytt mätsystem har implementerats på en delsträcka i Trafikverkets matarledningssystem på 132 kV i syfte att mäta upp förluster på delsträckan. Kraftöverföring till tågtrafiken i norra och mellersta Sverige sker med ett matarledningssystem på 132 kV som via transformatorstationer är anslutna till kontaktledningsnätet utefter banan. Matarledningen försörjs via omformarstationer som omvandlar elkraften till frekvensen 16⅔ Hz och är anslutna till det svenska elnätet. Den fallande vinkeln för spänningen från norr till söder i, det svenska elnätet, på grund av produktion i norr och konsumtion i söder medför oönskade effektflöden i matarledningssystemet om inte spänningens fasläge i omformarstationerna kompenseras för detta. Trafikverket har utvecklat ett effektstyrningssystem, med vilket det är möjligt att kompensera för den fallande vinkeln i det svenska kraftnätet, genom att styra vinkeln och spänningen i omformarstationerna. Därmed fördelas lasten mellan omformarstationerna mer effektivt och överföringsförlusterna minskar. Syftet med examensarbetet är att genom mätningar med ett nytt mätsystem fastställa hur stor energibesparing som åstadkoms av effektstyrningssystemet på en delsträcka i matarledningssystemet. Det befintliga mätsystemet som främst används för övervakning har inte tillräckligt god precision för analys av energiflöden. För att verifiera det nya mätsystemet ställs det i jämförelse mot det äldre med olika beräkningsmodeller för effektförlusterna, utifrån de parametrar som tillhandahålls från mätsystemen. Mätperioder har utförts veckovis för att jämföra energiflöden då effektstyrningssystemet är av respektive på. Resultaten visar på att effektbesparingen beräknas med störst precision genom att använda en π-ekvivalent modell för ledningar samt mätdata hämtat från det nyare mätsystemet. Detta eftersom det nyare mätsystemet påvisar bättre noggrannhet än det äldre, även om vissa förbättringar är möjliga. Den estimerade årliga energibesparingen med effektstyrningen påslagen, för den undersökta delsträckan, är 208,7 MWh, vilket är en minskad energiförlust på 33,2 %.