1,720,960 research outputs found
Design of a Partial Discharge Test Platform
No full textDesign of a Partial Discharge Test Platform author: Daniel Harmsen thesis advisor (mentor): Dr. Armando Rodrigo Mor abstract: Partial discharge (PD) measurements are an effective tool for insulation diagnostics and assessment. Therefore, a good understanding of these PD measurements is an essential part of an electrical engineer’s background knowledge. During this research project a PD test platform was designed and build for electrical PD detection. The setup included artificially created defects for six different types of PDs, with origins in positive and negative corona, internal discharge, floating electrodes, free-moving particles and surface discharge. These defects were designed to have a partial discharge inception voltage (PDIV) of around 10kV, and could easily be connected or disconnected from the setup. Therefore, it was possible to measure individual defects or a combination of them. This PD test platform was used during this research project to characterize the different PD types (single and multiple), and as a check for testing new clustering and pattern recognition techniques. In addition, the platform could also be used as a test platform for educational purposes and to train people and test equipment. In this thesis research project, the “initial step” towards PD defect origin recognition for AC voltage without any phase dependency was conducted with the use of time-resolved partial discharge (TRPD) analysis. This thesis shows that it is possible to conduct the time analysis and recognition for AC voltage for the artificially created defects. From the analysis in this thesis, it can be concluded that the TRPD analysis for PD recognition under AC voltage is as good as, or even better than, phase-resolved partial discharge (PRPD) analysis. For most of the data analysed, the TRPD analysis provides the same results compared to the PRPD analysis. However, further checking is needed, such as validating the findings with mathematical models. The thesis goals are to build a setup suitable for the research, determining the optimal combination of hardware/software to discriminate among different types of defects, and to realize experiments to validate the design.Electrical Engineering, Mathematics and Computer ScienceDC&E
Partial Discharge Analysis and Recognition in Cables with Medium Voltage DC
No full textWith the current state of power electronic conversion operating at Direct Current (DC) can in some cases be more efficient than ordinary Alternating Current (AC). DC voltage energy transmission and distribution is, thus, playing an increasingly important role. The continuity of the electrical energy supply is essential for a well-functioning society. At AC voltage problems with cables can in most cases be prematurely detected with Partial Discharge (PD) measurements. Partial discharges represent defects in the insulation system of electrical cables and devices. They can be categorized in three groups: corona, surface and internal discharges. By knowing the source of the partial discharges and quantifying the discharges, the dielectric condition of a cable can be estimated. At AC voltage the various patterns of partial discharges, also known as fingerprints, can already be recognized and the source of the defect can be determined. The trend for electrical power distribution is, thus, to use DC voltage instead of AC voltage. However, one problem that should be tackled is that partial discharges under DC voltage form a challenge in recognizing the source of the discharge. Therefore, it is still difficult to properly estimate the dielectric condition of the cable based on DC voltage partial discharges. To help overcome this challenge this master thesis research will try to find a relation between measured medium voltage DC partial discharge patterns and the actual source of the discharges. The influence of noise and data segregation of the measurements will be investigated. A method to separate multiple types of partial discharge from a single measurement will also be discussed. Furthermore, limits will be determined in how long a measurement needs to take in order to reliably detect the source of a certain defect. Four artificial PD defects were used to acquire specific data on the individual types of discharges at DC voltage. PD analysis has been done with a self-written Matlab program. By creating classification figures trends have been found that help recognizing the type of defect in a DC PD measurement. The influence of noise and data segregation on DC PD measurements has also been evaluated. Noise can significantly influence the classification figure. Therefore, noise should be prevented or filtered out prior to the classification process. A single noise waveform can already cause a large standard deviation in the classification figures. However, the calculated average values keep displaying the same trend. Thus, a single noise waveform does not hinder the recognition of the PD source. If due to high background noise lower amplitude PDs are lost, data segregation occurs. The physical relationships of time and charge between succeeding discharges will be distorted. To achieve a successful classification a minimum amount of PD waveforms is necessary, which has been investigated. For positive corona at least 250 PDs should be acquired to get the same trends in the classification figure as with 1000 PD waveforms. To be certain of a negative corona discharge, at least 300 PD-pulses should be recorded, instead of the reference measurement, which contained 903. The reference measurement with the internal discharge sample comprises of 578 waveforms. For proper classification a minimum of 300 discharges should be obtained. In order to be certain of surface discharges, 450 out of 999 waveforms are sufficient to create the same trends in the classification figure. To separate and classify individual discharge types from a multiple PD source measurement, cluster techniques are used. The cluster techniques used in this thesis are based on the (Energy versus Charge) and (Equivalent time versus Equivalent bandwidth) of a waveform. It has proven to be possible to classify and identify individual discharge sources. A classification of a certain cluster showed the same trends as in a reference surface discharge measurement. For negative and positive corona clusters 3 out of 4 classification figures comply with the reference measurements.Electrical Sustainable Energy trackElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Condition Assessment of Water in High viscosity Insulating Cable Termination Oil
No full textOil-filled terminations for high voltage XLPE insulated cables have been used for four decades in the Netherlands with a good service record. Prysmian would like to gain better insight into the effects of water contamination in insulating oil, to further extend the in-house experience and potential related failure mechanisms. High voltage termination is contained within a bushing that is filled with insulating cable oil. The insulating cable oil is a containment medium for the electric field lines and should have low dielectric losses, chemical inertness against the construction material, non-flammability and stable electrical property during prolong heating. The insulating oil is also self-healing, leaving no permanent conductive path in the fluid. The containment should be well-sealed to prevent any forms of leakage from the surroundings. The initial stages of the thesis seeks to inventory and address a few topics, mainly regarding water polluting oil. Studies will be done into the phenomena surrounding water within oil, the influence of water particles on the electrical performance of the oil, movement of water within the termination during temperature gradients and movement of water within the termination during electrical gradients. The next step is to inventory the current on-line and off-line tools available for measurements of water contents in oil. They would be AC voltage breakdown test, dielectric loss measurement, partial discharge detection, permittivity measurement and humidity check. Finally, the last phase would look to find mitigation techniques integrating the given inventories and observations, so as to formulate non-intrusive diagnostic methods to ascertain polluted terminations.Electrical Engineering, Mathematics and Computer ScienceElectrical Sustainable EnergyDC systems, Energy conversion & Storag
Partial Discharge Recognition of Defects in Gas Insulated Systems under DC Voltage
No full textThe thesis consists of 7 chapters. The first chapter will explain the background, motivations and the general overview of the thesis. Chapter 2 is a literature review describing the physics behind the creation of PDs. The conditions necessary for the occurrence of PDs are covered in addition to an analysis of the different types of PD in GIS ranging from corona, internal, surface and discharges due to electrically floating components for both AC and DC voltage. Chapter 3 presents the equipment available at TUDelft HV laboratory to create the set-up used for applying AC and DC voltages to the test object. The PD monitoring configuration are covered categorizing conventional and unconventional methods. Chapter 4 deals with signal processing of the PD data for classification of PD sources. Some quantities on which the analysis can be based, are discussed. Furthermore a distinction of quantities which are directly measurable by detection systems as direct data and the quantities or derived data derived through combinations or data analysis, will be made. In chapter 5, PD measurements using the conventional method of created defects in the HV laboratory are discussed. The defects are used to simulate insulation defects and the measurements in DC are analysed resulting in recognition graphs used for differentiating between the possible defects. Chapter 6 discusses the results of simultaneous measurements of PDs using the conventional method and RF techniques. The combined PD measurements on multiple defects are used to create plots of RF quantities to apparent charge. These plots are used for quantification of the relationship between the different techniques. Lastly, chapter 7 concludes the study and suggests future research related to the measurement of PDs in HVDC GIS using electrical partial discharge detection.DC Systems and Storage GroupElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Comparison of measurement methods for partial discharge measurement in power cables
No full textNowadays there are many partial discharge (PD) measurement systems on the market. There are systems that measure according to the IEC60270 standard (conventional measurement) and systems that don’t, the so called ‘’unconventional measurement systems’’. For PD measurement in power cables, measurement according to the standard has some shortcomings. Therefore development of unconventional measurement systems have taken place. Because there is no standard for these unconventional measurement systems, different manufacturers have developed different systems that use sensors with different bandwidths. Measurement with different systems could lead to different PD measurement results. Comparability of measurement results of different systems is desired in order to obtain an unambiguous result from different measurement systems for PD activity in the cable. Therefore there are investigated methods that create the possibility to compare measurement results of different systems that are used for PD measurement in power cables.DC and storageElectrical Power EngineeringElectrical Engineering, Mathematics and Computer Scienc
AC Electrical Breakdown Strength of Solid Solid Interfaces: A study about the effect of elasticity, pressure and interface conditions
No full textIn several electrical insulation components, such as cable connectors, joints and penetrators, various solid insulating materials are usually brought in contact, forming interfaces. The dielectric strength of these solidsolid interfaces is critical for the strength of the overall system. Especially in cases that the applied field has a tangential to the interface component, the solidsolid interface is regarded as a point of major weakness. Furthermore, these components are usually used in subsea applications and therefore the presence of water at the interface should be considered. The primary objective of this work is to examine how the elasticity of the solid material, the applied pressure and the interface condition is influencing the 50Hz/AC breakdown strength of the interface with a tangentially applied field. First, an prediction of the effect of varying elasticity modulus on the breakdown strength is attempted through theoretical modelling, adding to existing work. Following, the assumptions are verified by experimental testing in the High Voltage Laboratory of the Norwegian University of Science and Technology (NTNU). In order to facilitate the execution of the tests, a customised setup is built in the laboratory and identical test-samples are produced and prepared. Different pressure levels are applied for each material combination (XLPEXLPE, SIRSIR or XLPESIR) and for each interface condition (dry, wet or lubricated). The test data are treated using the Weibull distribution and are compared based on the minimum, mean and percentile value. It is seen that, generally, the minimum or the mean value is adequate to qualitatively compare the strength of different interfaces. Through the tests, it is also seen that the softer the materials that form the interface are, the lower is the elasticity modulus and thus the higher the breakdown strength. The influence of water and insulating oil at the interface is also explored through experimental testing in the lab. Therefore, the breakdown strength of wet and lubricated (oily) interfaces is examined and compared. Through analysing and accordingly presenting the test results, it becomes evident the the wet interface behaves poorly while the lubricated facilitates higher breakdown strength values. Further, the behaviour of an interface comprised by two materials with different elasticity is investigated (hybrid interface). The hybrid interface appeared to be the least affected by water, despite the low applied pressure.MSc Electrical Engineering - EWEMElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Control and Protection of VSC-based Multi-terminal DC Networks
No full textThe increasing global energy needs and the high integration of renewable energy generation have changed the requirements for the electricity grid. Countries are becoming unable to cover their energy demands with their own means and the need for power exchange between neighboring countries has increased. Consequently, power needs to be transmitted over longer distances and multi-terminal complex grids need to be created to facilitate the energy evolution. Contrary to the existing AC grids, HVDC is an appealing alternative for future grids. VSC technology has been the focus of recent HVDC research due to its inherent advantages. However, the use of fully-controllable switches becomes a disadvantage in case of DC contingencies. Thus far, opening the AC breakers has been the only way to clear DC faults, by completely de-energising the system and interrupting the power transfer with significant economic and societal consequences. Other protection concepts include multi-level converters with full-bridge submodules, which are able to limit the fault current; and control methods which identify the faulty lines. However, DC switch breakers are necessary to isolate the faulty line from the network, allowing normal operation to be resumed. The main contributions of this thesis are the comparison of different grid operating topologies under fault cases; and the impact analysis of different current limiting measures and control strategies on the developing DC fault currents. A four terminal grid in radial configuration was simulated using Matlab/Simulink®, and the natural fault response of the stations in most common HVDC grid topologies was studied. Additionally, two selective fault detection methods are proposed, which take into account the current direction on DC lines and the rate of rise of the fault currents. Four DC breaker technologies were simulated for all analysed grid topologies, and compared on the basis of the total DC fault interruption time and their influence on the system post-fault coordination and operation restoration. With the concepts analysed in this thesis, MTDC network system designers will be able to understand and tackle DC contingencies to facilitate an uninterruptible power flow between the different interconnected AC grids.Electrical Power ProcessingElectrical Sustainable EnergyElectrical Engineering, Mathematics and Computer Scienc
Partial discharge behavior of mineral oil based nanofluids
No full textA previous study showed that both mineral oil based nanofluids with 0.01% silica mass fraction and with 0.1% fullerene mass fraction have a higher AC breakdown strength than mineral oil. Breakdown occurs following discharge initiation and propagation in the oil. The breakdown strength value alone provides little information on the discharge process. Therefore, it is important to investigate the details of the discharge mechanisms in mineral oil and in nanofluids. Hence, this study focuses on the partial discharge (PD) behavior of mineral oil, silica and fullerene nanofluids. The total charge, voltage and pulse shape were recorded with the help of a high bandwidth PD measuring system. The discharge mechanism in mineral oil appeared to depend strongly on the polarity of the applied DC voltage. Under positive DC voltage, the silica and the fullerene nanofluids show increased inception voltage and a reduction of the total discharge magnitude compared to the reference mineral oil. Under negative polarity, inception voltage and discharge magnitude of the nanofluids and the reference mineral oil are virtually the sam
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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