Browsing by Author "Lehtonen, Matti, Prof., Aalto University, Department of Electrical Engineering, Finland"

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  • Demand Response Benefits for Major Assets of High Voltage Distribution Systems - Capacity Gain and Life Management
    (2015) Humayun, Muhammad
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Power systems require an adequate capacity and higher utilization efficiency for an economic and reliable supply of electricity. However, their utilization efficiency is ordinary owing to low load factor and reserve capacity needs. Moreover, the growth of electricity demand and aging infrastructure call for massive investments in form of expansions and replacements. Therefore, the power industry is searching for novel solutions to deal with the future needs. Demand response (DR), a load shaping tool in smart grids, can be a potential solution to the future needs. The aim of the dissertation is to assess the DR benefits of capacity utilization gain and better life management for major assets of high voltage grid. The study focuses on subtransmission grids because they have captured least attention in the prior research. Primary substation transformers have given special attention here due to their vital position in the system and high component cost. The aim of the dissertation is further divided into three tasks in order to distinguish the DR benefit among phases of operations and planning and various components. The first task proposes optimization models for utilization gain and life management of transformers by DR during normal and contingency operations. The second task offers tools for optimal capacity planning of transformers in primary distribution substations with and without considering DR. These tools incorporate all transformer related costs, their failure rate increase with age, and their salvage value based on loss-of-life. The third task determines the potential of DR in mitigating the redundancy needs of lines/cables, transformers, and busbars by comparing outage cost due to their contingencies. The simulations are performed using the developed models for typical Finnish systems. The results indicate the following notable deductions. The utilization efficiency of grid components can be substantially improved using DR that depends upon load shape and its DR capability. Also, DR offers significant better life management potential for transformers during both nor- mal and contingency operations. Moreover, the employment of DR along with remote switch- ing of load transfer between substations provides superior savings in transformer capacity planning as compared to that of manual load shifting. Furthermore, the optimal decisions of DR activations are essential in order to gain the intended DR benefits at a minimal expense. The power system utilities can use the models of this dissertation for making decisions of DR deployments. These deployments will be helpful in delaying or eliminating the capacity investments. Moreover, the tools of the second task will help asset managers for taking optimal planning decisions of transformer ratings and their replacement and maintenance schedules.
  • Design and Implementation of Partial Discharge Measurement Sensors for On-line Condition Assessment of Power Distribution System Components
    (2014) Shafiq, Muhammad
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Unplanned interruptions of power supply due to failure of critical components of the distribution network have considerable impact on the modern society. Efficient condition assessment can avoid the loss of critical components by early detection of incoming threats. One of the biggest shortcomings of today's progressing maintenance technology is the lack of low cost instrumentation solutions which are simple in implementation and easily applicable to the network. In this work partial discharge (PD) measurements have been considered for insulation condition assessment of distribution system components such as overhead covered conductors (CCs) and cables. A high frequency Rogowski coil induction sensor is designed for this purpose. An accurate electrical model of the sensor is necessary for efficient signal processing of the sensed signal and for reliable interpretation of the measured signal. A new method to determine the electrical parameters of Rogowski coil sensor is presented. In-depth analysis of the design stages of Rogowski coil is presented using experimental and simulated environment. Various geometrical designs of Rogowski coil are investigated to analyze the effects of geometrical parameters on high frequency performance of the coil. The guidelines presented regarding geometrical structure are useful when trading off the benefits for better mechanical and electrical design of such sensors. Location of the detected PD faults is an important task of the diagnostics system in power lines. The conventional techniques of locating PD faults have been known for a single section of a power line. However, these techniques are not suitable for power lines having multi-sections or for branched line networks. In this work, finding the location of PD fault on a power line is recognized as a two stage function; (i) identification of the faulty section, and (ii) location of fault point on the identified section. The direction of arrival (DOA) technique is introduced to identify faulty section whereas fault point location can be determined by conventional techniques. The technique is equally applicable for CC lines or cable networks. The DOA technique is integrated over a cable feeder and an on-line automated condition monitoring and diagnostic scheme is proposed. Low cost, non-intrusive installation and favorable operating features of Rogowski coil sensor make it suitable for development of an enhanced and automated diagnostic system which can easily be integrated into the distribution network.
  • Dynamic Scenario Modelling in Electricity Distribution System Asset Management
    (2014) Palola, Jussi
     School of Electrical Engineering | Doctoral dissertation (monograph)
    The life of individuals, societal welfare and global economics are deeply interconnected with power systems in a multidimensional manner. A change in one entity affects the whole system. This thesis is a research journey from electrical distribution systems to global economics, and finally to power transformer unit asset management. The objective is to investigate dynamic scenario modelling in power system asset management and apply it to a distribution system operator’s power transformer fleet assets. The asset management of a distribution system is directly coupled to the economy, both globally and locally. Economic attributes affect electrical network asset management from many directions simultaneously: electricity demand, network expansion requirements, and component, construction and operational expenditures. A comprehensive cost function is formed and applied with different economic scenarios for asset management. Revealing the dynamics of power transformer asset management with scenarios is relevant in an increasingly turbulent global environment. This thesis offers an approach to assess the techno-economic dependencies in electricity distribution system asset management for more pertinent decision making. Understanding the dynamic balance between asset management and overall expenses is increasingly important while seeking economic efficiency and return on investments.
  • Economic Impacts of Electric Power Outages and Evaluation of Customer Interruption Costs
    (2015) Küfeoğlu, Sinan
     School of Electrical Engineering | Doctoral dissertation (article-based)
    Electricity has become a vital part of the modern societies. Thanks to using electrical equipment in almost every aspect of the life, in case of an interruption the daily routine is paralyzed. Whether the electricity is a social right or not is still debatable. No matter it is a social right or commodity, improving the electric power reliability so that more people (or customers) will have the opportunity to make use of this service is in favor of everyone in the market. Europe has been known to have robust, well developed and well planned electric power systems. This meant considerably high level of reliability for the European societies until the beginning of 2000's. Nevertheless, during the last decade there has been an increase in the number of extreme weather related disasters throughout the world. Natural disasters have become the primary threats for the continuity of electricity service in Europe and in the rest of the world. Studying customer interruption costs and proposing credible and practical estimation methods is a challenging task. The necessity of this research arose from the lack of widely accepted and easy to adopt approaches in the field. Each customer segment has its own distinct electric power consumption and dependence characteristics. This fact indicates the necessity of analyzing each customer group separately and proposing unique customer interruption costs estimation techniques. Having a developed power system and easiness to reach credible data for analysis, Finland is a proper country to study the economic impacts of the electric power interruptions. The ultimate goal of this research is to provide outage cost estimations which will be; customer specific, utilizing publicly declared and objective data, demanding less time, less money and less effort, easy to duplicate in any part of the world and providing credible and sound results. In order to achieve these goals, in this research, the customers are divided into three main segments; industry customers, service customers and residential customers. Different and unique customer interruption costs estimation methodology has been proposed for each customer segment.
  • Finding Value in Big Data - Statistical Analysis of Large Data Sets with Applications in Electric Power Systems
    (2015) Koivisto, Matti
     School of Electrical Engineering | Doctoral dissertation (article-based)
    A growing volume of data is becoming available in the field of electric power systems. The hourly automatic meter reading (AMR) electricity consumption data available from small customers, such as households and small businesses, is a significant new data source. For example, geographic data, wind speed data and phasor measurement unit data add to both the quantity and the significant variety in the available data. This thesis presents how these large data sets can be utilized in power system studies using statistical methodology. A visualization and clustering of a large AMR data set is presented, and consumption models are then estimated for the discovered clusters, i.e., consumer groups. Statistical modelling is applied to wind speed and wind generation data from multiple locations, with the emphasis on understanding the effect of the geographical distribution of wind power. In addition, combined statistical modelling of stochastic distributed generation (e.g., wind and solar power) and electricity consumption is presented, which allows the effects of stochastic generation to be analysed at the distribution system level. Interesting system operation conditions (e.g., power flows, consumption, wind generation) affecting the expected damping of the 0.35 Hz inter-area oscillation in the Nordic power system are identified, and their use in the short term prediction of damping is demonstrated using statistical methods. Several different geographically varying risk factors affecting the expected fault rates in power distribution systems are also identified, and the use of the estimated fault rates in automatic network planning is presented. It is argued that the statistical analysis of electricity consumption and generation can also be used in automatic network planning. Although the volume and variety of data are important in enabling data analyses, the value that can be extracted from the data using appropriate data analysis methods is fundamentally the most important aspect. In this thesis, multiple data visualization techniques are presented for finding patterns in the large data sets. The discovered patterns are then modelled using statistical data models. The need to model the probability distributions of the relevant random variables in detail is emphasized. This is especially important in wind power modelling, and was achieved using Monte Carlo simulation.
  • Geographical Perspectives on the Development of Power Distribution Systems in Sparsely Populated Areas
    (2013) Saarijärvi, Eero
     School of Electrical Engineering | Doctoral dissertation (monograph)
    It has been proposed that the present power distribution overhead lines should be replaced by underground cables, to address the concerns related to major disturbances caused by snow loads and storms. However, in an objective comparison of different network development strategies, the special characteristics of each of the line types and the terrain must be considered when determining optimal network topologies. In sparsely populated areas the need for cost-effective solutions tailored to best fit the specific terrain and operational environment is emphasized. In this thesis, a method capable of providing a network topology planning algorithm with line type specific characteristics of the operational environment, including an accurate dynamic topographic model involving variable costs, was developed. The work included case studies, the initial data of which was provided by Finnish network utilities from a variety of environments. Applying the developed methodology using a terrain model, also a contribution of this thesis, to the case studies provided general perspectives on the factors affecting the network topologies and the relative merits of different development strategies. The results were compared with the literature, which enabled further assessment of the validity of the methodology and parameterization used in this thesis. The results of the case studies showed that the optimal penetration of sectionalization is greatly affected by the load density. However, the quantity, quality and valuation of the interruptions affect the basic level of the penetration. Then again, optimally placing reserve connections was found to be a much more complex task, being partly affected by not only the geographical distribution of the loads but also by the characteristics of the terrain. While comparing fully backed-up against cost-optimally backed-up network topologies, the potential for utilizing lightweight structures was observed to have a considerable impact. Further, the characteristics of the terrain were found to affect not only cabled networks, but also the topologies of cost-optimal overhead line networks. The developed method for finding the cost-optimal network topology by using an accurate geographic model of the operational environment in terms of life cycle cost surfaces was found to be an efficient means for comparing different circumstances and network topologies and their mutual interactions. A close connection between the network data available in network information systems and the various geographic information sources was also recognized. Further, the means to effectively utilize this connection in the different processes of network planning and operation is presented.
  • Noise analysis of high voltage capacitors and dry-type air-core reactors
    (2013) Hurkala, Marcin
     School of Electrical Engineering | Doctoral dissertation (monograph)
    The goal for this work was to create new methods to study the noise production in some power system components, namely capacitors and reactors. In the case of the capacitors the work was started by trying to create a FEM model of the individual capacitor element as well as each of the capacitor sides. In the end individual element proved to be too complicated to be modeled, but the sides were modeled using the assumption that they're individual clamped plates. To find out how the individual element behaves one was subjected to direct current of various amplitudes and the compression was measured with a dial indicator at various points. The compression was deemed to be linearly dependent on the distance from the middle point of the surface of the element. In order to measure the response of the whole capacitor, a vibration measurement was used. Vibration transducer was used on each side to get the overall vibration response of each side when the capacitors were fed various inputs. The responses were measured in three different temperatures. The direct acoustic response was measured in the anechoic chamber. This yielded new information about the directivity of the noise produced by the capacitors at the different frequencies. The results of the vibration measurement could be also compared to the acoustic measurements. The comparison resulted in partially incoherent results. Final measurement related to the capacitors was one where the viscosity of the capacitor oil was measured. This allowed to partially explain the variations in the vibration response at the different temperatures. The noise measurement of the reactors is difficult due to the high magnetic field caused by them. Since the direct measurement wasn't an option, a plastic tube extender was used to move the sound further away from the reactor where it could be then measured with regular microphone. The tube extender was used in one field reactor measurement, in one controlled reactor measurement, and its response was measured in the anechoic chamber. As a result it was found that the tube extender can be used in this kind of measurements, and perhaps could be in the future to use in recognizing the faults of the reactors before they become severe.