@phdthesis{Samborsky2017, author = {Samborsky, Michael}, title = {Conceptual aspects of future High Voltage Direct Current (HVDC) electrical power transmission networks}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-43658}, school = {BTU Cottbus - Senftenberg}, year = {2017}, abstract = {A continually growing demand for reliable energy supply makes existing power systems more heavily loaded and evokes engineers and experts to look for feasible immediate solutions in power energy transmission. One of these solutions might be a bulk power transmission network at extra high voltages based on direct current. Currently, high voltage direct current (HV DC) transmission has been only realized in point-to-point systems and back-to-back arrangements. Thus, the next logical step in this development would be an HV DC network. In principle, it might have certain advantages over a conventional high voltage AC system, as it could be less closely meshed covering larger areas and transmit higher electric power with lower losses. However, no well-grounded investigations concerning possible layout and operation of an HV DC network are publicly available. Experience from the HV DC lines does not allow to make substantial conclusions regarding the requirements for an HV DC network. Therefore, some basic questions on the operation of an HV DC network need to be answered mainly from systems simulations.}, subject = {HVDC; Power transmission; Transient process; Energy system; High voltage; HG{\"U}; Energie{\"u}bertragung; {\"U}bergangsprozess; Energiesystem; Hochspannung; Elektrisches Energiesystem; Hochspannungsgleichstrom{\"u}bertragung}, language = {en} } @phdthesis{Venna2015, author = {Venna, Karthik Reddy}, title = {A Simulation analysis to improve the dielectric strength inside High Voltage Vacuum Interrupters}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-33551}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {Vacuum circuit breakers are expected to be one of the possible alternatives for SF6 circuit breakers in transmission voltages up to 230kV because of the excellent insulation as well as environmental friendly characteristics of vacuum. But for higher voltages, maintaining the electrical insulation inside and outside the interrupter tube is very important and becoming a challenge for the design engineers. Normally a vacuum interrupter consists of metal shields sandwiched between the ceramic insulator blocks inside the tube. The primary purpose of these metal shields is to protect the insulator walls by avoiding metal vapor deposition during the arcing process. On the other hand, these metal shields also influence the electric field distribution inside the interrupter tube. The presence of the metal shields may reduce the dielectric strength of the interrupter tube if proper measures are not taken. This research is devoted to provide the information about the possible areas inside and outside the interrupter tube that are considered as critical in terms of dielectric strength because of the presence of metal shields. Possible solutions are also given in this thesis to overcome the high field stress in these critical areas with the help of 2D simulations that are simulated in ANSYS Maxwell. The critical areas and their respective solutions presented in this work are (1) unidentified edges outside the interrupter tube which are formed by the metal shields that are inserted between the ceramic blocks. These edges, at high field stress, may act as a source of discharges between the interrupter tube and the outer insulator. This problem can be reduced by the combination of using a pressurized insulating gas (which is in this case N2) between interrupter tube and outer insulator and by extending the unidentified edges and covering them with field grading rings which are conductive in nature. (2) Triple junctions (Vacuum-Ceramic-Metal shield) are the sources of high field stress inside the interrupter tube and are considered as a primary source of Secondary Electron Emission Avalanche that takes place on the (3) ceramic surface. The triple junction emissions can be avoided by properly designing the insulator geometry at point of contact with the metal shield. In addition, inserting metal parts of certain depth at the both ends of the ceramic insulators can also reduce the field stress at the triple junctions and avoid surface flashovers on the ceramic surface. (4) The gap between the metal shield and the contact rod is also considered to be a critical area which can be highly stressed (field) if the geometry of metal shield curvature is not properly designed. Various metal shield curvatures are proposed and simulated and an optimum geometry is suggested that reduces the electric field stress between the metal shield and contact rod. Using this optimized metal shield curvature, the diameter of the interrupter tube can be reduced considerably which in turn reduces the size of the interrupter tube.}, subject = {High voltage vacuum interrupter; Triple junctions; Field grading rings; Metal shields; ANSYS maxwell; Triple-Punkte; Feldsteuerringe; Elektrische Feldst{\"a}rke; Hochspannungs-Vakuumschaltr{\"o}hre; Metallabdeckungen; Vakuumschalter; Hochspannungsschalter; Durchschlagsfestigkeit}, language = {en} } @phdthesis{Challagondla2015, author = {Challagondla, Naresh Kumar}, title = {Behaviour of water drop on the insulator surface and study of electric field distribution on parallel insulators under DC}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-33718}, school = {BTU Cottbus - Senftenberg}, year = {2015}, abstract = {With the recent developments in electrical transmission system, HVDC transmission for long distances has become feasible. With this development, many insulators are being used in HVDC system. Different kinds of insulators are situated at different places (example: desert, near to sea, agriculture area, etc.) so they will get expose to different types of pollution. Pollution affects the behavior of insulation in terms of breakdown and withstand capability. The application experience of insulators under HVDC conditions is limited. There is a necessity to understand the flashover performance and to recognize key parameters in the design and dimensioning of insulators used under HVDC conditions. This dissertation presents the difference between the analysis of partial breakdowns at AC and DC. The dissertation explains the behavior of a water drop on insulator shed surface energized with DC. It deals with the moving water drop and hanging drop at the edge of the shed. There are many situations where insulator structure should be in parallel. For example, the structure of insulators in vertical disconnector equipment often is parallel. If insulators are arranged in parallel, then the behavior of the electric field is totally different. It is important to know the behavior of these insulators used in HVDC system. This report also explains the pollution and non-pollution behavior of parallel insulators energized with DC. The results can be a source of information to optimize the design and dimensioning of HVDC insulators, especially in pollution conditions.}, subject = {HVDC; High-Voltage insulators; Pollution performance; Water drop behavior; Parallel insulators; Ansys Maxwell; HG{\"U}; Hochspannungsisolatoren; Verhalten bei Verschmutzung; Verhalten von Wassertropfen; Parallele Isolatoren; Hochspannungsisolator; Wassertropfen}, language = {en} }