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.

Stochastic Characteristics of Load Profiling in Distribution Systems based on AMR measurements

Abstract: In order to enable the key applications provided by smart grid, a dynamic distribution system state estimator has to function properly giving the real time knowledge of a distribution network load profiles. However, due to unavailability of enough measurements and lagging communication of the measured data, the current system cannot readily access measurements in real time. Therefore a practical load modeling technique has to be applied to provide real time distribution system load profile estimates with the respective confidence intervals. Nevertheless, modeling individual customer loads is far statistically complicated and computationally prohibitive for real time application. The customer loads are not always normally distributed but rather a combination of normal distribution, lognormal distribution, generalized pareto and many others. In this study, models of primary heating type load classes are used to represent individual customers. A statistical formulation based on clustered customer groups’ hourly consumption model is used to calculate aggregated substation loads and day ahead load forecasts with the respective confidence intervals. The stochasticity of customer loads when aggregated at distribution substation is investigated for four customer type load classes.

Experimental investigation of lightning initiated flashover faults in MV lines

Abstract: Direct lightning stroke to an overhead line conductor can produce a flashover across insulator causing a fault on the power network. A medium voltage (MV) overhead line with grounded cross arm will experience a single-phase fault whereas a multiphase (two-phase or three phase) fault is likely to occur when the cross arm is ungrounded in the event of a lightning strike. This paper investigates the characteristics of lightning initiated flashover faults in unshielded medium voltage (MV) lines with different types (metallic/wood) and configurations (grounded/ungrounded) of cross arm. The lightning impulse voltage is applied to one phase of a three-phase overhead line and the experimental flashover characteristics of single-phase and two-phase flashover faults are investigated. The total CFO of the line is also calculated using up and down method. The effect of cross arm braces on the flashover path and the variation in the magnitude of voltage build-up in the nearest phase is also analyzed. The tests have been performed under dry and wet conditions with both positive and negative polarities.

Influence of rainfall on lightning flashovers from trees to medium voltage bare and covered conductors

Abstract: In this paper, a laboratory experiment was conducted to compare the performance of lightning discharge characteristics of bare conductor (BC) and covered conductor (CC), resulting from very-close lightning strokes to trees. Special attention is paid to the influence of rainfall on the lightning arc characteristics. All the experiments are performed using full-scale configurations. Other factor investigated is the effects of tree-to-line clearance. The studies reveal a substantial amount of new information which is required to fully understand the true behavior of very-close lightning interaction with power conductors in rainfall, which is often the true lightning situation.

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.