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.

Effect of Terminating Resistance on High Frequency Behaviour of Rogowski Coil for Transient Measurements

Abstract: Partial Discharge (PD) current measurements have been widely used to assess the insulation condition of power components. Rogowski coil is a low cost current sensor specifically meant for high frequency transient diagnostics such as PDs in high voltage (HV) power apparatus. This paper presents the design of Rogowski coil for transient measurements. For the designed prototype of Rogowski coil, correct selection of terminating resistance is of high importance to calibrate its response for accurate measurement of the PD current waveforms. Effect of terminating resistance for the coil model is analysed based on theoretical, practical and simulated investigations. Simulated model of the coil is used to determine the behaviour of induced current through non-physical inductive and capacitive elements of Rogowski coil. The Electromagnetic Transient Program-Alternative Transient Program (EMTP-ATP) is used to implement and to analyze the model of Rogowski coil. The comparison of practical and simulated results validates the designed model of the coil. The paper explores EMTP-ATP as an efficient tool to analyze and modify the transient behaviour of Rogowski coil for high frequency pulse measurements.DOI: http://dx.doi.org/10.5755/j01.eee.19.7.2070

Priority Assessment of Online Monitoring Investment for Power System Circuit Breakers—Part II: Determination of Optimum Number

Abstract: The proper and reliable operation of circuit breakers (CBs) directly affects the reliability and continuity of electricity services in a power systems. Condition-based maintenance (CBM) is the best economic CB maintenance strategy through its online monitoring (OLM) possibilities. Since there is a large number of CBs in a power system, to equip all CBs with OLM systems is not economically justifiable however. This paper, as the second part of a two-part paper, presents an effective optimization framework to find the optimal number of CBs to be monitored online as the kernel of CBM process. To prove its feasibility, the proposed approach is applied to the IEEE Roy Billinton Test System, which includes 32 CBs. The impacts of interest rate and load interruption cost variations as well as nonoptimum selection of CBs for monitoring on the results are also discussed in this paper. The results of numerical analyses of the case study presented in this paper demonstrate how the proposed method can be employed for maintenance management of power system CBs.

Estimating the annual frequency and cost of voltage sags for customers of five Finnish distribution companies

Abstract: Frequency and cost of voltage sags for customers of five Finnish distribution companies were evaluated. For voltage sag frequency calculations the method of fault positions was applied. Only sags caused by short circuit faults in medium voltage distribution networks were considered. Sag frequency below considered 50% magnitude showed quite low numbers. However the cost related to this sag magnitude revealed that voltage sags are a relevant power quality issue having economic significance.

Multiobjective Photovoltaic Sizing With Diverse Inverter Control Schemes in Distribution Systems Hosting EVs

Abstract: Worldwide, photovoltaic (PV) and electric vehicles (EVs) have intensively been integrated into distribution systems. As a result, different operational issues can be observed due to PV generation variability and EV stochastic characteristics. In this article, an optimal sizing approach of multiple PVs in the existence of EVs is proposed. The proposed approach minimizes both the total voltage deviations and overall energy losses, prevents active PV power curtailment, and considers numerous constraints of PV, EV, and the distribution system. The features of the proposed approach are the considerations of PV, EV, and load uncertainties via incorporating their probabilistic models. Besides, it models arrival/parting times of EVs, the required state of charge (SOC) of EV batteries based on initial SOCs and remaining parking periods, and controlled/uncontrolled charging. Furthermore, diverse control schemes of the interfacing PV inverter are formulated in the proposed optimization model. To effectively solve this comprehensive model with conflicting subfunctions and variables, a two-level multiobjective evolutionary algorithm based on decomposition with fuzzy sets is developed. The upper optimization level accurately optimizes the sizes of multiple PVs, while the lower one optimizes charging/discharging of EV batteries, PV inverter oversize, and PV reactive power. The results prove the effectiveness of the proposed approach.

Earth faults and related disturbances in distribution networks

Abstract: The characteristics of the earth faults and related disturbances, recorded in medium voltage overhead distribution networks during the years 1998-1999 are described. Altogether 316 real cases were analysed. The use of subharmonic oscillation and harmonic distortion was investigated, as a means of anticipating faults. Arcing faults made up at least half of all the disturbances, and were especially predominant in the unearthed network. Fault resistances reached their minimum values near the beginning of the disturbances. The maximum currents that allowed for autoextinction in the unearthed network were comparatively small.

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.