Matti Lehtonen

Bio: Matti Lehtonen is an academic researcher from Aalto University. The author has contributed to research in topics: Fault (power engineering) & Electric power system. The author has an hindex of 40, co-authored 694 publications receiving 8559 citations. Previous affiliations of Matti Lehtonen include Razi University & New York University.

Mitigation of Lightning Flashover from Tree to Medium Voltage Aerial Cable Using Shield Wire

Abstract: This paper presents the performance and protection of medium-voltage (MV) aerial cables against lightning faults by means of laboratory experiment and digital modeling. With the series of laboratory tests, practical examination of lightning hazard to shielded and unshielded aerial cables is conducted, and the need for shield wire protection is established. For the purpose of simulation studies, digital models are developed by using Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and its transient analysis of control system features. The performance of lightning flashover overvoltage on shielded and unshielded aerial cable is evaluated with the developed digital models. The evaluation is made by considering a direct lightning strike on wooden poles, messenger wires, and nearby trees. Based on the experimental and simulation results, practical recommendations are proposed for improvement in lightning performance of aerial cables. This study offers possible solutions for the protection of aerial cables against lightning flashover, induced overvoltage, and direct lightning strike, which may improve electricity reliability and availability to customers.

An advanced model for automatic fault management in distribution networks

Abstract: An automatic computer model, called the FI-model, for fault location, fault isolation and supply restoration is presented. The model works as an integrated part of substation SCADA and medium voltage distribution network automation systems, including protective relays and AM/FM/GIS. In the model, three different techniques are used for fault location: computed fault distance; analysis of fault indicator readings; and statistical analysis of the line section fault frequencies. Once the faulty section is identified, it is automatically isolated by the remote control of line switches, and supply is restored into the remaining parts of the feeder.

Optimizing energy cost via battery sizing in residential PV/battery systems

Abstract: Application of renewable sources of energy is vital for the mankind due to global warming. Residential buildings consume major portion of electricity. Therefore, a grid-connected photovoltaic system of domestic level with battery storage backup (PV/storage system) is addressed in this article. This system has a significant effect on decreasing energy costs and contributes to meet the requirements of a nearly net-zero energy building. In this article, Mixed Integer Linear Programming (MILP) is applied to optimize the energy cost of a single-family house with battery energy storage for four different scenarios of installing solar panels. Optimization is performed on monthly scale for a house in Helsinki, Finland. The numerical results indicate that it is reasonable to integrate a storage in grid-connected PV systems in residential applications and represent the impact of battery size on household's monthly energy cost.

Simple fault path indication techniques for earth faults

Abstract: Fault indication is the key element in any fault management system. In case of short circuits, fault indication is straightforward, but especially in ungrounded and compensated neutral networks, the single phase fault currents are typically so small that simple fault current threshold detection hardly gives any satisfactory results. The problem can be solved by combining neutral voltage measurement to the sum current measurement using directional relay characteristics. However, the requirement of both current and voltage measurements makes the solution cost prohibitive especially when retrofitting in the existing secondary substations. Hence, there is the need for a simple but reliable earth fault indicator which is based on current measurements solely. This paper takes the above mentioned challenge and compares a number of possible fault indication solutions which are using local current measurements at the secondary substations only. The methods presented use either the sum current measurement directly, or are based on the comparison of the measured phase currents using symmetrical components.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The Design and Analysis of Experiments

Abstract: THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

World energy outlook

Abstract: This chapter discusses leading problems linked to energy that the world is now confronting and to propose some ideas concerning possible solutions. Oil deserves special attention among all energy sources. Since the beginning of 1981, it has merely been continuing and enhancing the downward movement in consumption and prices caused by excessive rises, especially for light crudes such as those from Africa, and the slowing down of worldwide economic growth. Densely-populated oil-producing countries need to produce to live, to pay for their food and their equipment. If the economic growth of the industrialized countries were to be 4%, even if investment in the rational use of energy were pushed to the limit and the development of nonpetroleum energy sources were also pursued actively, it would be extremely difficult to prevent a sharp rise in prices. It is evident that it is absolutely necessary to pursue actively the development of coal, natural gas, and nuclear power if a physical shortage of energy is not to block economic growth.