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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Analys av elkvalité vid en mindre industri i Norrlands inland / Analysis of power quality at a small industry in middle of Sweden

Frisk, Tord January 2016 (has links)
Från den elektriska likströmsmotorn, till dagens komplexa trefassystem med motorer styrda av frekvensomformare, skapas det idag mer ”skräp” på elnätet än någonsin. Det har givit oss ett modernt problem som ofta är osynligt, men som kan ställa till med rejäl oreda om man har otur. Permascands fabrik är belägen i Ljungaverk och har problem med ljud i ett ställverk. Mätningar görs därför i anläggningen för att samla in mätdata och utifrån dessa skapa en nulägesbeskrivning när det gäller elkvalité. En tidigare mätning av anläggningen på grund av de upplevda problemen refereras i stora drag, som en bakgrundsgenomgång och förståelse för problemet. Ett steg i att upplysa personalen om begreppet elkvalité görs i samband med en studie i form av en enkät med en inledande text och några enkla frågor. Slutligen görs en jämförelse mellan fabriksanläggningen och en liknande anläggning på samma elnät, där uttaget av reaktiv effekt i förhållande till aktiv effekt studeras över tid. Under de mätningar som gjorts vid transformatorns nedsida visade det sig att det i förhållande till standarden EN 50160 finns för höga nivåer av flimmer. Utifrån den enkät som personalen vid fabriken fått besvara visar det sig att många inte känner till så mycket om begreppet elkvalité, men att man upplever att det är bra elkvalité vid fabriken. En rekomendation är att fortsätta arbetet med att söka efter ursprunget till kraftiga strömvariationer och de höga strömövertonshalterna då de påverkar transformatorn. Även att man på sikt budgeterar för att höja kunskapen om elkvalité bland de anställda för att kunna ta adekvata beslut vid inköp av utrustning. / From the electric DC-motor to today’s complex three-phase systems with motors controlled by frequency converters, more "junk" is created on the electric grid than ever. This has given us a modern problem that is often invisible, and can cause a substantial mess if you are unlucky. Permascand plant is located in Ljungaverk and has problems with sound in one of their switchgears. Measurements are therefore made in the plant to collect data and create a status report for power quality. A previous measurement of the plant, which was done because of the perceived problems, is refered in broad terms as a background review and understanding of the problem. One step to educate staff about the concept of power quality is done with a study in the form of a questionnaire with an introductory text and a few simple questions. Finally, a comparison is made between the plant and a similar factory on the same electric grid, where the reactive electrical energy is compared to the active electrical energy over time. During the measurements that were made at the transformer downside, it turned out that in relation to the standard EN 50160, there are high levels of flicker. Based on the questionnaire that staff at the plant had to answer, it turns out that many do not know much about the concept of power quality, but they feel that there is good power quality at the factory. A recommendation is to continue the work to find the origin to strong variations in the current and the harmonic current, because they affect the transformer. It is also recommended, that the budget in the long term is made to raise awareness of power quality among the employees, to be able to take proper decisions when purchasing new equipment.
2

Cost-Benefit Assessments of Some Power Quality Improvement Options

Leou, Chian-Shian 03 July 2001 (has links)
With the increase of sensitive loads in industrial and commercial customers, more attention has been paid to the power quality problems. Voltage sag is among the major power quality problems that cause interruptions in production lines that result in significant losses. Power quality mitigation devices, that provide different protection levels, can be adopted to match individual customer¡¦s special needs. This thesis presents a cost-benefit assessment of various voltage sag mitigation options at locations with different types of distribution feeders and customers. Simulation results have revealed that using the assumed power quality cost data, the installation of small capacity and low cost UPS has the highest benefit/cost ratio in all the options tested.
3

Identification of weak areas and worst served customers for power quality issues using limited monitoring and non-deterministic data processing techniques

Woolley, Nick C. January 2012 (has links)
The current international trend in distribution networks is towards increased monitoring. This trend is being driven by distribution network operators (DNOs) who hope that through increased monitoring, they will be able to optimise capital and operational expenditure and thus operate a more efficient networks. One of the key areas of focus relating to the increased interest in distribution network monitoring is power quality. Power quality disturbances affect consumers by interrupting equipment or halting industrial processes and can result in very significant financial losses. DNOs are also financially impacted by power quality issues if they breach regulatory limits or contractual arrangements. To extract value from power quality monitoring, DNOs must process and then interpret data from a variety monitoring devices placed at different locations all potentially measuring different quantities. The challenge of how best to extract useful and practical power quality information from disparate monitoring devices is the subject of this thesis. This thesis describes and develops monitoring techniques for two power quality phenomena: voltage sags and unbalance. The research presents new techniques which can graphically identify the weakest areas and the worst served customers for voltage sags and unbalance. All the developed techniques utilise non-deterministic methods (such as statistics and artificial intelligence) to deal robustly with network and measurement uncertainties. This thesis can be dissected into four areas: voltage sag monitoring, optimal power quality monitor placement, voltage unbalance monitoring and identification of the weakest areas and worst served customers for both issues. The first section of this thesis is dedicated to voltage sags. This section introduces a multi-step process to identify and estimate the impacts of voltage sags within networks. The first stage in this process is classification and detection where several different classification methods (including immune inspired techniques) are compared to determine which algorithms work best under the context of limited monitoring. The research then proposes a novel robust method for performing fault location and voltage sag profile estimation using multiple monitors. The method pays particular attention to the errors in measurement inputs and identifies the most likely location for both the fault location and the voltage magnitude using statistical methods. The voltage sag monitoring research concludes by defining the probable impacts of voltage sags on customers, and by introducing a new measure known as the sag trip probability. The second major section covered by this thesis is optimal monitor placement. This thesis presents a comprehensive methodology which enables network operators to place monitors in locations best suited for voltage sag monitoring based on future likely topological and loading changes. The third major section covered by this thesis is unbalance monitoring. A three phase distribution system state estimation model is developed which can estimate the location and impact of unbalance within the network, without assuming the loading is balanced. The final section of this thesis shows how the worst served customers and the weakest areas of the network can be identified presents for both voltage sag and unbalance using limited monitoring and the developed techniques. The results are presented graphically using a series of topological heat maps, and these show visually how the techniques could work to monitor a distribution network.
4

Power quality programme awareness : framework for developing countries

Sultan, Saad Saleh January 2013 (has links)
In recent years, Power Quality Programmes (PQPs) have become one of the most recent services offered to electrical distribution companies, both private and state suppliers. This is due to the sudden increase in the number of concerns over power quality (PQ) problems. The aim of this research is to study the implementation of a PQP framework, and the obstacles and barriers faced by Libyan Distribution Networks (LDNs) in implementing a PQP. Firstly, to identify the most critical success factors that would have a major impact on PQP implementation in LDNs. Five Critical Success Factors (CSFs) for PQP were identified to examine the level of power quality in LDNs. They are PQ awareness, PQ disturbances, PQ management commitment, PQ employee’s participation and training and PQ customers’ satisfaction. It revealed that all five CSFs were significantly affected by the level of PQ awareness, and the suspension of PQP implementation. An appropriate PQP framework was developed for the purpose of this study to guide LDNs as a case study in developing countries. The proposed PQP framework model was validated based on the identified CSFs, and the barriers and benefits of PQP, which were analysed using different techniques based on both SPSS and NVivo software. The PQP framework was developed from the findings based on the responses of 397 PQ survey participants, and supported by 44 face-to-face semi-structured interviews conducted with professionals and expert LDNs staff. Out of the 16 PQP barriers, 13 were statistically significant, which indicated that Libya distribution systems have already surmounted various barriers to implementing a PQP effectively. The developed PQP framework consisted of three essential phases. Phase one is designed to increase the level of awareness, while phase two involves preparation for PQP, which contains seven crucial requirements. Phase three, which is the implementation, is designed to determine both the weaknesses and obstacles, and is designed to increase the awareness level. This framework encourages and guides the implementation teams to have an obvious and clear awareness and vision of how to prevent existing obstacles from reappearing in different forms, leading to long-term PQP improvements. There were 11 overall benefits of PQP implementation, which would have a positive impact on LDNs.
5

An Analytical Framework for Power Quality Monitoring in Enterprise-level Power Grid

Ali, Sardar 21 December 2015 (has links)
Due to the high measuring cost, the monitoring of power quality is non-trivial. This work is aimed at reducing the cost of power quality monitoring in power networks. Using a real-world power quality dataset, this work adopts a learn-from-data approach to obtain a device latent feature model, which captures the device behavior as a power quality transition function. With the latent feature model, the power network could be modeled, in analogy, as a data-driven network, which presents the opportunity to use the well-investigated network monitoring and data estimation algorithms to solve the network quality monitoring problem in power grid. Based on this network model, algorithms are proposed to: 1) intelligently place measurement devices on suitable power links to reduce the uncertainty of power quality estimation on unmonitored power links, 2) estimate the power quality in unmonitored segments of a power network, using only a small number of measurement points, and 3) identify a potential malfunction device in the network. The meter placement algorithms use entropy-based measurements and Bayesian network models to identify the most suitable power links for power quality meter placement. Evaluation results on various simulated networks including IEEE distribution test feeder system show that the meter placement solution is efficient, and has the potential to significantly reduce the uncertainty of power quality values on unmonitored power links. After deploying power quality meters on selected links, a MaxEnt-based approach is presented to estimate the power quality on the unmonitored lines. Compared to other existing methods such as MCEM, the MaxEnt-based approach is much faster while maintaining similar estimation accuracy. Convergence time of the MaxEnt algorithm is particularly important when the network size increases and we need to do the estimation in real time. Finally, using readings from our metered locations, we propose a prediction model that derives an acceptable device behavior to identify a potential malfunction device in the power grid. Simulation results show that our predictive model accurately detects the malfunction devices in the power network and can be used to make proper recommendations of device maintenance and replacement. / Graduate
6

Power Quality Analysis of a Three-Phase Cycloconverter Under Variable Operating Conditions

Palani, Kevin 01 June 2010 (has links) (PDF)
The objective of this study is to observe the correlations between variable operating conditions and power quality parameters for a three-phase to single-phase cycloconverter. The cycloconverter is examined in its most straightforward form without additional output filters or elaborate control methods. Variable operating conditions include input frequency, output frequency, and resistive load size. The power quality parameters of interest are power factor, input current total harmonic distortion (THD), output voltage THD, and efficiency. The scope of the project includes analytical calculations, PSpice simulations, as well as a hardware implementation. The results show that output frequency has minimal effect on power quality. High input frequencies tend to yield less efficiency and larger loads yield higher efficiency. Total harmonic distortion undesirably peaks at a combination of low input frequency and high output frequency. Extrapolations can be made for the cycloconverter operating at different frequencies and loads based on the trends observed within the test matrix.
7

Variable speed drives for power factor correction in the water sector

Keys, Erin Marie 07 October 2014 (has links)
While solar photovoltaic (PV) panels can offset fuel, emissions, and water use at the power plant, high levels of installed rooftop PV capacity can have negative impacts on the stability and efficiency of the local grid because of power factor (PF) degradation. Specifically, electric utilities have noted voltage fluctuations from solar PV that occur more dynamically than legacy, electromechanical voltage regulation solutions like capacitor banks are designed to correct. At the same time, distributed power electronics devices like inverters can provide the type of dynamic voltage support that utilities seek to maintain reliability while juggling load growth and a greening grid. Using data from Pecan Street Inc. Smart Grid Demonstration Project in Austin, Texas and Austin Water Utility (AWU), this research examines the potential for a three-phase, four quadrant variable speed drive (VSD) in the water sector to provide PF correction to a load pocket of 63 homes experiencing varying levels of PV penetration. In the analysis, the VSD is not reserved for voltage support; instead it is predominantly used to drive a 30 kilowatt (kW) centrifugal sewage pump. The simulation determines the degree to which the VSD can restore PF to a threshold of 0.95, slightly below the targeted value for Austin's electric utility. Further, the economic viability of using the VSD as a grid device is explored by comparing the per unit cost of the PF correction it provides to a current utility solution for dynamic voltage regulation. / text
8

Impact of decentralized power on power systems

Morales, Ana A B 28 September 2006 (has links)
Wind generation is one of the most successful sources of renewable energy for the production of electrical energy. Wind power offers relatively high capacities, with generation costs that are becoming competitive with conventional energy sources. However, a major problem to its effective use as a power source is the fact that it is both intermittent and diffuse as wind speed is highly variable and site-specific. This is translated in large voltage and frequency excursions and dynamically unstable situations when fast wind power changes. Very high wind speeds will result in sudden loss of wind generator production. The requirement to ensure that sufficient spinning reserve capacity exists within the system to compensate for sudden loss of generation becomes crucial. From the utilities operators’point of view, the primary objective is the security of the system, followed by the quality of the supplied power. In order to guard the system security and quality of supply and retain acceptable levels, a maximum allowed wind power penetration (wind margin) is normally assumed by the operators. Very conservative methods are used to assess the impact of wind power and the consequences turn to under-exploitation of the wind power potential in a given region. This thesis presents the study of actual methods of wind power assessment, divided into three parts: 1. Part I: Impact on the Security of Power Systems 2. Part II: Impact on the Power Quality 3. Part III: Impact on the Dynamic Security of Power Systems
9

Power Quality State Estimation

Farzanehrafat, Ali January 2014 (has links)
Traditional state estimation whereby the state of the system is assessed based on a limited number of measurements is a well established tool for steady-state situations where the frequency of the system is 50 Hz. Previous contributions have looked at extending this concept to the power quality area. This area of research is called Power Quality State Estimation (PQSE) and represents a class of techniques. Under the umbrella of PQSE, the main contribution of this work is taking Transient State Estimation (TSE) on step further. A new three-phase formulation for TSE using the Numerical Integrator Substitution (NIS) will be detailed. NIS approach, also known as Dommel's method, gives a numerical solution to describe the transient behaviour of a dynamic system at discrete time points. The new transient state estimator is implemented and verified by applying the proposed algorithm to a real distribution test system. It's performance and accuracy are investigated in presence of measurement noise, background harmonics, multiple faults, etc. The conducted study has shown this technique has a great potential.
10

Voltage sag and momentary interruption ride-through for adjustable speed drives

van Zyl, Annabelle 15 December 1998 (has links)
The awareness of electric power quality has increased over the past decade as electronic equipment has become more susceptible to power disturbances. The most disruptive power disturbances are voltage sags and momentary interruptions and their effect on adjustable speed drives (ASDs) is studied in this thesis. Several solutions have been suggested to provide only voltage sag ride-through to ASDs, but most solutions focus on ASDs with passive rectifiers since they hold the largest share of the market. This thesis focuses on ASDs with active rectifiers, which is an emerging and growing market due to the advantages of four quadrant operation and reduced harmonics offered. A solution is presented which provides an ASD with an active rectifier with the capability to ride through the most common sags in order to reduce the frequency at which the ASD trips and thereby increase its reliability. In order to provide ASDs with the capability to ride through momentary interruptions, it is necessary to interface an energy storage system to the ASD. Flywheels, ultra-capacitors and batteries are evaluated for use in an energy storage system to provide voltage sag and momentary interruption ride-through and a detailed comparison of six systems based on these technologies is presented. The interface circuit between the energy storage system and ASD has a significant influence on the performance of the energy storage system and therefore interface circuits to ASDs with passive and active rectifiers are studied. The addition of an ultra-capacitor energy storage system to an ASD with an active rectifier in order to provide ride-through of deeper sags and momentary interruptions is studied and a fuzzy logic controller is designed to enhance system performance. Initially, no communication between the ASD and the ultra-capacitor system is assumed and the ultra-capacitor system can therefore be added as a retro-fit to an existing ASD. It is, however, foreseen that the market for ASDs with ride-through capability of voltage sags and momentary interruptions will grow and the concepts for an integrated design of an ASD and an energy storage system are presented. / Graduation date: 1999

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