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.

A Stochastic Assessment of PV Hosting Capacity Enhancement in Distribution Network Utilizing Voltage Support Techniques

Abstract: The low voltage (LV) network’s constraints are prone to violations with the introduction of distributed energy resources at the customer vicinity. This study assesses the technical aspects of the realistic Finnish distribution network with varying photovoltaic (PV) penetration and quantifies the hosting capacities (HCs) of different regions. Moreover, to maximize the network’s HC, having the overvoltage issue, different voltage control strategies are employed comprising on-load tap changer (OLTC), reactive power control (RPC) of inverters, network reinforcement (NR), and hybrid approaches. HC relative to different country-specific over-voltage limits are defined and the best voltage control technique is assessed, utilizing the stochastic approach of Monte Carlo simulations to model the uncertainty in the LV network’s probabilistic variables. Moreover, combined medium voltage (MV)/LV network simulations are conducted to compare with the LV only simulations results. Technically, NR is the best approach to maximize the HC of a particular region but economically it is not proven a feasible one. The results presented that the OLTC employment will maximize the PV penetration if the overvoltage limit derived from EN 50160 is implemented and doubles the HC in the stricter-voltage-limits’ scenarios, which can be maximized by the RPC inclusion in cohesion with OLTC. Moreover, RPC only strategy can be employed in the cases of low PV penetration scenarios, when OLTC will be proven the more expensive option. As the voltage violation limit becomes stricter, the hybrid approach of OLTC and RPC will be the best strategy.

Pre-emptive arc fault detection techniques in switchgear and controlgear — Part II

Abstract: The significant benefits of preemptive arc-flash protection and the online condition monitoring of electrical equipment are quite well known. Our continuing research focuses on the development of new advanced sensor technologies that are cost-effective, reliable, and efficient for the early detection of faults in order to predict impending arc-flash occurrences in mediumvoltage and low-voltage switchgear and controlgear. More extensive and detailed measurements regarding significant defects that lead to an arc-flash event have been completed since the original work in Part I was completed. A more detailed analysis of the results of this additional testing is presented in this paper. It has been documented that the two major noncontact causes that lead to an arc-flash event in switchgear are insulation degradation and thermal stresses. This paper covers the detailed measurement results under both of these conditions. New sensor technologies for both the partial discharge measurement and the thermal detection are introduced and evaluated. An effective signal processing technique, which is needed for extracting the essential indication of a developing fault, is also presented. Finally, this paper outlines how a preemptive arc detection system can be connected to protection, the programmable logic controller, or the supervisory control and data acquisition.

Lightning-Induced Overvoltages Transmitted Over Distribution Transformer With MV Spark-Gap Operation—Part I: High-Frequency Transformer Model

Abstract: In Finland, distribution transformers are frequently subjected to lightning strokes. Therefore, it is worthy to study the voltage transferred to the secondary terminal of the transformer due to lightning strokes hitting the primary terminals. In order to do conduct this study, the high-frequency model of the distribution transformer is to be investigated. In this paper, an accurate and simplified high-frequency model of the distribution transformer under lightning strokes is presented. The proposed model is introduced based on two-port network theory where its parameters are calculated at two resonance frequencies experimentally measured. The model is suitable for unloaded and loaded conditions and it is experimentally verified under different balanced loads considering two different practical distribution transformers. Then, the model verification is extended to study the impact of medium-voltage spark-gap operation on the transmitted voltage. The experimental results have validated the proposed transformer model.

Earth fault location based on evaluation of voltage sag at secondary side of medium voltage/low voltage transformers

Abstract: The main reasons for installation of power quality meters in distribution transformer substations are power quality monitoring and global evolution of electrical network towards the ‘smart grid’. In case that all measurements from the meters are properly synchronised and centralised, new possibilities of control or evaluation of the network are enabled. This contribution proposes the possibility for an earth fault localisation with the aid of synchronised data recorded on the low-voltage side of the medium voltage/low voltage transformers in compensated neutral distribution networks which are equipped with auxiliary resistor for short-time increasing of the active part of the fault current. The described method uses voltage sags evoked by connecting of the auxiliary resistor for locating the faulty section. The proposed method is tested with the help of numerical model which presents a part of the distribution network.

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.