Aspects and directions of internal arc protectio

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Büchin automaateista

Tutkielma käsittelee Büchin automaatteja. Ensiksi esitetään aakkostot, merkkijonot ja kielet, jonka jälkeen edetään deterministiseen ja epädeterministiseen äärelliseen automaattin. Osoitetaan, että näiden ilmaisuvoima on sama, ja todistetaan Kleenen lause äärelliselle automaatille. Sen jälkeen esitetään äärettömät merkkijonot, ω-säännölliset kielet, deterministien Büchin automaatti ja epädeterministinen Büchin automaatti. Lopuksi osoitetaan Kleenen lause Büchin automaatille ja että deterministisen Büchin automaatin ilmaisuvoima on aidosti heikompi kuin epädeterministisen Büchin automaatin.Valinnaisten opintojen tutkielm

Variaatiolaskentaa ja sen sovelluksia

Tutkielman aiheena on variaatiolaskenta, jossa tarkastellaan funktionaalien ääriarvoja. Variaatiolaskentaa tarkastellaan funktionaalianalyysin näkökulmasta ja aiheeseen syvennytään tunnettujen variaatio-ongelmien kautta joista tunnetuin lienee Brachistochrone, josta variaatiolaskennan katsotaan saaneen alkunsa. Tutkielmassa esitellään variaatiolaskennan peruslauseista useampi versio, tutustutaan hyvin syvällisesti Eulerin yhtälöön, kuten myös Eulerin yhtälön invarianssiin. Osansa tutkielmasta saavat myös funktionaalin differentiaali eli variaatio ja variaationaalinen derivaatta. Lisäksi tutkielmassa tarkastellaan yksinkertaisinta variaatio-ongelmaa. Sovelluksina esitetään ratkaisut valon kululle epähomogeenisessa aineessa ja geodeesille sylinterin pinnalla

Overcoming illiteracy through game-based learning in refugee camps and urban slums

Today 3.7 million refugee children are out of school. The ones forcibly displaced across borders are likely to remain there much of their childhoods and go through an entire school cycle in exile. Without access to quality education, these children have diminished likelihood of breaking free from circular dependency, scarcity, and marginalization. At the same time education sectors globally are adapting to the inevitable increase of digital learning. This study was motivated by the potential availability of digital education, and it argues for non-formal digital game-based learning in refugee and low-resource environments, with a special focus on early literacy. The participants (N = 359) consisted of marginalized, most vulnerable, and out-of-school children aged between 5 and 8. They participated in interventions in Pakistan and Bangladesh for 90 days, two hours a day. The children played digital learning games at their own pace following the learning goals of their national curriculums. The learning outcomes were measured using the EGRA framework. The study found that the intervention children achieved or surpassed the learning gains of a control group studying through formal education. These results suggest that digital learning games show promise for improving early grade literacy, even in low-resource contexts.Peer reviewe

Non-Directional Earth Fault Passage Indication in Isolated Neutral Distribution Networks

In this paper, two new methods for locating single-phase to ground faults in isolated neutral distribution networks are proposed. The methods are based on the analysis of symmetrical sequence currents. They are solely based on currents, not requiring voltage measurement. The first method employs only the zero sequence current and the second one utilizes the negative sequence current in combination with the zero sequence current. It is revealed why using only zero sequence current with a simple threshold is insufficient and may lead to false results. Using the proposed methods, earth faults with high resistances can be located in isolated neutral distribution networks with overhead lines or cables.© Writers. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license, http://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

Intermittent earth fault passage indication in compensated distribution networks

An intermittent or restriking earth fault is a special type of earth fault that is common mostly in compensated cable networks. A great deal of effort has gone into protection against this type of fault. However, locating this fault has not received much attention. Therefore, there is a need to have a reliable method for locating this fault to repair the damaged cable. In this paper, the principles of a new method developed for locating transient intermittent earth faults on distribution networks are presented. The proposed method employs negative and zero sequence currents, and no voltage measurement is required, which means the proposed method has the potential to reduce cost when implemented in practice. It is intended mainly for typical intermittent earth faults in cable distribution networks where the typical fault resistance is in the range of a few ohms. Real data obtained from practical field tests is used to explain the phenomenon. A series of disturbance recordings obtained from field tests validate the proposed method.©2021 Elsevier. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/ This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication.fi=vertaisarvioitu|en=peerReviewed

Light-weight IEC 61850 GOOSE based LoM protection for smart grid

This paper presents a novel Loss of Mains (LoM) protection method based on IEC 61850 General Object Oriented Substation Event (GOOSE) protocol. With the increased penetration of distributed generation (DG), the requirements for LoM or anti-islanding protection has become common in the electric utilities. The development of Smart Grids including extensive communication capabilities enables also communication based LoM approaches. Since IEC 61850 standard based systems are the mainstream in the substation communication, expanding this technology deeper in the distribution network provides interesting solution for communication based LoM protection. The standard IEC 61850-7-420 defines logical nodes (LNs) suitable for this purpose but there are not yet available devices applying this part of the standard. Therefore in this research, a light-weight 61850 GOOSE based LoM solution has been developed and demonstrated applying a microcontroller and available open source software. This paper introduces object modeling according to IEC 61850-7-420 defined LNs and an implementation applying GOOSE messages and microcontroller. The validity of the light-weight implementation is demonstrated with a simple laboratory setup that has been used for measuring the message latencies.fi=vertaisarvioitu|en=peerReviewed

An economic study of combined heat and power plants in district heat production

Combined heat and power plants are playing an essential role in Finland to reduce carbon dioxide emissions in district heat production. Some of the existing district heat producers need to adopt renewable energy sources to eliminate the use of fossil fuels. The northern countries face a challenge to tackle significant fluctuations of district heat consumption between summer and winter seasons concerning the production cost and the environmental impact of heat production. The municipality of Sodankylä is reorganising the district heat production to reduce emissions by constructing new wood-fuelled CHP plants. These plants will contribute to the existing district heating network. The profitability of CHP plants and the environmental impact in the region need evaluation. Results reveal that the profitable investment for the construction of CHP plants requires 16% subsidy with the predicted cost of heat production at 3.36 €/MWh. CO2 emissions from fossil fuels can potentially eliminated by adapting renewable fuel in the existing plant. CH4 and N2O emissions from district heat production reduced by 78% and 53%.© 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).fi=vertaisarvioitu|en=peerReviewed

Online condition monitoring of MV cable feeders using Rogowski coil sensors for PD measurements

Condition monitoring is a highly effective prognostic tool for incipient insulation degradation to avoid sudden failures of electrical components and to keep the power network in operation. Improved operational performance of the sensors and effective measurement techniques could enable the development of a robust monitoring system. This paper addresses two main aspects of condition monitoring: an enhanced design of an induction sensor that has the capability of measuring partial discharge (PD) signals emerging simultaneously from medium voltage cables and transformers, and an integrated monitoring system that enables the monitoring of a wider part of the cable feeder. Having described the conventional practices along with the authors’ own experiences and research on non-intrusive solutions, this paper proposes an optimum design of a Rogowski coil that can measure the PD signals from medium voltage cables, its accessories, and the distribution transformers. The proposed PD monitoring scheme is implemented using the directional sensitivity capability of Rogowski coils and a suitable sensor installation scheme that leads to the development of an integrated monitoring model for the components of a MV cable feeder. Furthermore, the paper presents forethought regarding huge amount of PD data from various sensors using a simplified and practical approach. In the perspective of today’s changing grid, the presented idea of integrated monitoring practices provide a concept towards automated condition monitoring.fi=vertaisarvioitu|en=peerReviewed

Alternative solutions for advanced security of supply

The restrictions regarding the maximal length of outages especially under major storms has resulted in massive underground cabling projects in the network companies in Finland and Sweden. Due to these expensive investments the network fees of many network companies have increased to the extent that the customers have reacted. In both countries, the authorities have announced restrictions to the rate of increase of the network fees. Thus, the network companies are now searching for alternative solutions to underground cabling. This task is here addressed by performing case studies on the network of a rural primary distribution substation area of the Vaasan Sähköverkko distribution company.Technologies surveyed include low voltage (LV) connected battery energy storage (BES), implementation of the 1000 V distribution system in low-power feeder laterals, feeder automation(FA) and both mobile and fixedbackup power generation. The impact of implementing these technologies is then compared to increasing the underground cabling level of the case study network. The results are typical investment costs, distribution system reliability indices, annual total outage costs, annual regulatory incentives and payback times of the alternative technologies as well as recommendable implementations of different technologies. The study presents a cost-effective strategy for the infrastructure of electricity distribution of sub-urban and rural distribution areas.fi=vertaisarvioitu|en=peerReviewed