1,721,091 research outputs found
The current interruption process in vacuum analysis of the currents and voltages of current-zero measurements
No full textThe circuit breaker helps protecting vulnerable equipment in a power network from hazardous short-circuit currents by isolating a fault, when it occurs. They perform this task by extinguishing a plasma arc that appears as soon as the breaker's contacts separate, and through which the short-circuit current flows. In an AC network, the current's value runs periodically through zero, and each current zero provides the breaker with an opportunity to quench the arc, because here, its energy input is temporarily zero. Due to the inductive nature of most short-circuit networks, the voltage tends to rise immediately to its maximum value after the current interruption. This complicates the current interruption process for breakers, because just after they have been loaded with the arc, they have to cope with this recovery voltage as well. To ensure their reliability, new circuit breakers are subjected to tests with artificially generated short-circuit currents and recovery voltages, with values that are appropriate for the network in which they are intended to use. These tests follow strict rules, recorded in standards such as the IEC 62271-100, about the size and shape of the current and voltage waveforms. Specialised institutes, such as the High Power Laboratory at KEMA, perform such tests and hand out certificates to breakers that pass all tests. The certification process usually provides little more information than that the breaker passed a test, or not, and it would be beneficial for both the certification institute, and the breaker's manufacturer, to obtain more information form the tests. Such analysis on SF6 breakers has already taken place with success in the past, and this work applies it to vacuum circuit breakers. Vacuum circuit breakers (VCBs) are the most widely used type of breakers to protect distribution level networks, with operating voltages of up to 72.5 kV. This thesis analyses the electrical signals from short-circuit interruptions in vacuum, to detect trends and indicators on the breaker's performance. For this purpose, it describes the test circuits and the measuring techniques, used to obtain the electrical behaviour of the vacuum circuit breaker just after current zero. This includes the efforts to reduce the distortion from the strong electric and magnetic fields that inevitably involve a short-circuit test. After its extinction, the vacuum arc leaves residual plasma behind, which provides a conducting path through which a post-arc current can flow. Since the post-arc current is the most distinctive electrical signal in a vacuum current interruption, the analysis mainly focusses on this phenomenon. The residual plasma decays within microseconds, thereby finishing the breaker's transition from a near perfect conductor to a near perfect insulator. The thesis pays special attention to the measuring equipment that was used to track these fast changes in the signals (sub-microsecond), and its large dynamic ranges (from kilo amperes to tenths of amperes, and from volts to kilo volts). In addition to the post-arc current research, the thesis analyses the VCBs reignition behaviour. Since VCBs are created to prevent reignition, they had to be subjected to much higher currents and voltages than their rated values, to force them to reignite. These results, and the results from the post-arc current research, provide new insight in the current quenching mechanism in vacuum. Finally, this thesis also pays attention to the interaction between the electrical circuit and the VCB after current zero. To this end, it describes how existing models are extended with theories and insights that emerged from this research. The result has been implemented as a function block in Matlab's SimPowerSystems, which facilitates the incorporation of the model in different electrical circuits.Electrical Engineering, Mathematics and Computer Scienc
Bouwmethodiek voor high-rise woongebouwen: De ontwikkeking van een beslismodel om vroeg in het ontwerpproces de keuze te kunnen maken voor de meest economisch bouwmethode
No full textHigh-rise residential buildings can be built in a broad variety of manners. The creation of a decision model with which the most economic construction methodology for a specific project can be obtained, was the goal of this research project. It has been carried out in cooperation with the Dutch contracting firm Boele & van Eesteren. Problem definition The choice for the construction method of a building is often based on a contractor’s knowledge, culture, equipment and thoroughness in which a project- and process analysis is carried out. Whether the selected construction method is the most economical is not always analyzed in an integral manner. Furthermore, in case alternative construction methods are analyzed, excess risks on construction costs and construction time are not always explicitly taken into account. Research My research is carried out by answering the following research questions: 1. How is the development of high-rise residential buildings in the Netherlands and which construction methodologies are used? 2. Which construction methodologies are essential for integration into the decision model? 3. In which manner can social developments in the Netherlands influence the choice for a construction methodology? 4. What are, as seen from the building practice’s point of view, the most important project related influence factors on the choice for the construction methodology, and how can these be integrated into a decision model? 5. In which manner can excess risks on construction costs and construction time be efficiently integrated into a cost and time estimation? Results 1. Since 2000, 27 high-rise residential buildings were built and in the coming years another 27 projects are being realized. The construction methodologies that are mostly used are ‘tunnelen’ (48%), ‘prefab’ (24%), ‘klimmen’ (10%), ‘staal’ (5%) and ‘traditioneel’ (2%). 2. Because of the their high degree of repetition, concurring building costs and relatively high building speed, ‘tunnelen’, ‘prefab’, and ‘klimmen’ are essential for integration into the decision model. 3. Working with social responsibility is something that is being done by more an more contractors in the Netherland, but as long as there will not be a financial incentive for this, it will not be a part of the decision model. 4. Influence factors: building time, building costs, contractors expertise, design, market, location and logistics. They can be integrated to select technically possible methods and carry out a design related optimization. 5. Carry out a quantitative risk analysis based on a risk database providing statistical data. Conclusions and recommendations The market for high-rise residential building is growing. A few construction methodologies are leading in use and should always be analyzed in a project analysis. Working with social responsibility is growing but not always integrated as policy. It deserves further research in which way this can be integrated into companies policies. Integrating a quantitative analysis of excess risks can add to choosing the most economic construction methodology. It deserves further research into how this integration can be obtained as well as research into the creation of a risk database.Design and ConstructionCivil Engineering and Geoscience
Schakelen in energienetten: techniek, gevolgen en beheersaspecten : handboek PATO cursus, Technische Universiteit Eindhoven, Elektrum Arnhem, 10-11 juni 2004
No full textSchakelen in energienetten: principes van moderne schakelende componenten en hun toepassing in elektriciteitsnetten : handboek PATO cursus, Technische Universiteit Eindhoven, 13-14 juni 2002
No full textFault Current Control in the Transmission Network: An Electromagnetic Transient approach
No full textTransmission System Operators (TSO's) are facing an increase of fault current levels in their networks due to the expansion of generation capacity. This thesis investigates three possible fault current limiting measures in the Dutch transmission grid which is operated and maintained by TenneT TSO. In order to evaluate the behavior of the fault current limiting measures, two independently operating grid models were established and validated. The examined fault current limiters consisted of a current limiting reactor (CLR) and a superconducting fault current limiter (SCFCL). The possibility of substation splitting was also investigated. All three measures reduced the short-circuit levels successfully to values within the electromechanical and thermal withstand levels of the power system. Simulation results revealed that the SCFCL has a significantly lower impact on the rate-of-rise-of-recovery-voltage (RRRV) of the circuit breaker (CB) as compared to the CLR. Additional measures were presented to keep the RRRV of the CLR within the dielectric withstand levels of the CB as specified in the IEC 62271-100.Track Electrical Power EngineeringElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Schakelen in energienetten:principes van moderne schakelende componenten en hun toepassing in elektriciteitsnetten : handboek PATO cursus, Technische Universiteit Eindhoven, 13-14 juni 2002
Get PDFSimulation of lifetime arching stresses on high-voltage circuit breakers by testing
No full textText in Russia
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