Effects of modern variable frequency drive on the reliability of an old crane induction motor

The work aims to analyze the possibilities of utilizing old crane driving AC induction motors in modern pulse-width-modulated variable frequency drives. Bearing currents and voltage stresses are the two main problems associated with modern IGBT inverters, and they may cause premature failure of an old induction motor. The origins of these two problems are studied. An analysis of the mechanism of bearing failure is proposed. Certain types of bearing currents are considered in detail. The most effective and economical means are chosen for bearing currents mitigation. Transient phenomena of cables and mechanism of over voltages occurring at motor terminals are studied in the work. The weakest places of the stator winding insulation system are shown and recommendations are given considering the mitigation of voltage stresses. Only the most appropriate and cost effective preventative methods are chosen for old motor drives. Rewinding of old motors is also considered.

Evolutionary Ecology of Mountain Birch in Subarctic Stress Gradients: Interplay of Biotic and Abiotic Factors in Plant-Plant Interactions and Evolutionary Processes

In nature, variation for example in herbivory, wind exposure, moisture and pollution impact often creates variation in physiological stress and plant productivity. This variation is seldom clear-cut, but rather results in clines of decreasing growth and productivity towards the high-stress end. These clines of unidirectionally changing stress are generally known as ‘stress gradients’. Through its effect on plant performance, stress has the capacity to fundamentally alter the ecological relationships between individuals, and through variation in survival and reproduction it also causes evolutionary change, i.e. local adaptations to stress and eventually speciation. In certain conditions local adaptations to environmental stress have been documented in a matter of just a few generations. In plant-plant interactions, intensities of both negative interactions (competition) and positive ones (facilitation) are expected to vary along stress gradients. The stress-gradient hypothesis (SGH) suggests that net facilitation will be strongest in conditions of high biotic and abiotic stress, while a more recent ‘humpback’ model predicts strongest net facilitation at intermediate levels of stress. Plant interactions on stress gradients, however, are affected by a multitude of confounding factors, making studies of facilitation-related theories challenging. Among these factors are plant ontogeny, spatial scale, and local adaptation to stress. The last of these has very rarely been included in facilitation studies, despite the potential co-occurrence of local adaptations and changes in net facilitation in stress gradients. Current theory would predict both competitive effects and facilitative responses to be weakest in populations locally adapted to withstand high abiotic stress. This thesis is based on six experiments, conducted both in greenhouses and in the field in Russia, Norway and Finland, with mountain birch (Betula pubescens subsp. czerepanovii) as the model species. The aims were to study potential local adaptations in multiple stress gradients (both natural and anthropogenic), changes in plant-plant interactions under conditions of varying stress (as predicted by SGH), potential mechanisms behind intraspecific facilitation, and factors confounding plant-plant facilitation, such as spatiotemporal, ontogenetic, and genetic differences. I found rapid evolutionary adaptations (occurring within a time-span of 60 to 70 years) towards heavy-metal resistance around two copper-nickel smelters, a phenomenon that has resulted in a trade-off of decreased performance in pristine conditions. Heavy-metal-adapted individuals had lowered nickel uptake, indicating a possible mechanism behind the detected resistance. Seedlings adapted to heavy-metal toxicity were not co-resistant to others forms of abiotic stress, but showed co-resistance to biotic stress by being consumed to a lesser extent by insect herbivores. Conversely, populations from conditions of high natural stress (wind, drought etc.) showed no local adaptations, despite much longer evolutionary time scales. Due to decreasing emissions, I was unable to test SGH in the pollution gradients. In natural stress gradients, however, plant performance was in accordance with SGH, with the strongest host-seedling facilitation found at the high-stress sites in two different stress gradients. Factors confounding this pattern included (1) plant size / ontogenetic status, with seedling-seedling interactions being competition dominated and host-seedling interactions potentially switching towards competition with seedling growth, and (2) spatial distance, with competition dominating at very short planting distances, and facilitation being strongest at a distance of circa ¼ benefactor height. I found no evidence for changes in facilitation with respect to the evolutionary histories of plant populations. Despite the support for SGH, it may be that the ‘humpback’ model is more relevant when the main stressor is resource-related, while what I studied were the effects of ‘non-resource’ stressors (i.e. heavy-metal pollution and wind). The results have potential practical applications: the utilisation of locally adapted seedlings and plant facilitation may increase the success of future restoration efforts in industrial barrens as well as in other wind-exposed sites. The findings also have implications with regard to the effects of global change in subarctic environments: the documented potential by mountain birch for rapid evolutionary change, together with the general lack of evolutionary ‘dead ends’, due to not (over)specialising to current natural conditions, increase the chances of this crucial forest-forming tree persisting even under the anticipated climate change.

Runkopalkkien valmistuksen kehittäminen

Diplomityössä kehitetään runkopalkkien valmistusta Juhani Haavisto Oy:ssä. Palkkien valmistusta käsitellään hitsauksen ja koneistuksen osalta. Työn alussa perehdytään hitsauksen mekanisointiin, hitsattavuuteen, lastuttavuuteen sekä hitsaus- ja koneistuskiinnittimiin teorian osalta. Tämän jälkeen esitellään valmistettava tuote. Kokeellisessa osassa esitetään runkopalkkien valmistusvaiheet ennen ja jälkeen kehityksen. Esille tulevat niin hitsauksen kuin koneistuksenkin valmistusvaiheet. Tutkimuksessa selvisi, että uudet hitsaus- ja koneistuskiinnittimet pienentävät työaikoja mm. mahdollistamalla laajemman mekanisoidun hitsauksen ja pienentämällä kappaleen kääntöihin ja vaihtoon kuluvaa aikaa. Lopuksi pohditaan mahdollisia jatkokehityssuunnitelmia, jotka koskevat uuden hitsauskuljettimen ja uusien lisäaineiden käyttöä.

Sähköinen tarkastuslista rakennusteollisuuden laadunvalvonnan tukena

Rakennusteollisuus on tunnettu useita muita aloja hitaammasta uuden teknologian käyttöönotosta. Yleisesti käytössä on hyvin perinteinen paperia ja kynää hyödyntävä tiedontallennuskäytäntö. Paperin käytössä tiedon tallennusvälineenä on useita ongelmia kuten säilytettävyys ja hallittavuus, joista päästään eroon siirtymällä sähköiseen tiedon tallennukseen. Laadun varmistamiseksi voidaan käyttää tarkastuslistoja, jotka toimivat tarkastuksien suorittajan muistin tukena. Muutettaessa tarkastuslista sähköiseen muotoon, voidaan välttyä paperisen tarkastuslistan ongelmilta, kuten käsialan tunnistamiselta ja merkintätapojen vaihtelevuudelta. Tässä diplomityössä käsitellään rakennusteollisuuden laadunhallinnan nykytilaa sekä sähköisen tarkastuslistan käyttöä rakennusteollisuuden laadunvalvonnassa. Lisäksi esitellään prototyyppi sähköisestä tarkastuslistasta osana laadunvalvontaa. Sähköinen tarkastuslista toteutetaan dynaamisesti niin, että tarkastuslistojen pohjalta on mahdollista luoda käyttöliittymä kyseessä olevan listan mukaisesti päätelaitteelle. Sähköisen tarkastuslistan prototyyppi on toteutettu WWW-sovelluspalveluna (World Wide Web), joka mahdollistaa useiden erilaisten päätelaitteiden hyödyntämisen.

Managing Customer Retention in Health and Fitness Club Industry

The objective of this study is to resolve how customer retention is managed in Finnish health and fitness clubs, and how is this comparable with the theoretical aspects of customer retention. It is also discussed how the process leading to customer retention is handled, and what the essential elements of customer retention and loyalty are specifically in the health and fitness club industry. In addition, it is discussed to what extent do health and fitness club companies implement the elements of customer retention in their businesses. Finally, there is discussion about the relationship and priority between the behavioral and attitudinal methods of creating retention in the companies. The data was collected by interviewing the management of six health and fitness clubs from different geographical regions in Finland. Results indicated that the most important constructs concerning customer retention were switching barriers, pricing strategy, competitive aspect, corporate image, service quality, employee retention, and customer satisfaction. In addition, the implementation of customer retention was found to vary between different sized companies and companies from different geographical locations. Moreover, it was discovered that the companies put more effort in constructs that are considered to create customer loyalty instead of retention.

Overvoltage Mitigation Techniques in Wind Power Generators

Advancements in power electronic semiconductor switching devices have lead to significantly faster switching times. In motor and generator applications, the fast switching times of pulse width modulated (PWM) inverters lead to overvoltages caused by voltage reflections with shorter and shorter cables. These excessive overvoltages may lead to a failure of the electrical machine in a matter of months. In this thesis, the causes behind the overvoltage phenomenon as well as its different mitigation techniques are studied. The most suitable techniques for mitigating the overvoltage phenomenon in wind power generator applications are chosen based on both simulations and actual measurements performed on a prototype. An RC filter at the terminals of the electrical machine and an inverter output filter designed to reduce the rise and fall times of voltage pulses are presented as a solution to the overvoltage problem. The performance and losses of both filter types are analysed.

Protection of the high-voltage equipment with reduced insulation strength

Power transformer is the most expensive equipment on a substation. It is always necessary to get needed benefit with the lowest expenses. Producing of power transformers with reduced insulation strength is one of the possible ways to reduce expenses. Exploitation of such transformers was begun in the end of 70-th in the last century. Protection from overvoltages was done with valve-type magnetic combined surge arresters with increased blanking voltage during switching overvoltages. Nowadays there is the necessity of replacement of those devices. That’s why modernized nonlinear surge arrester was invented. This master’s thesis is focused on the use research of that modernized device in comparison with usual nonlinear surge arresters. The goal is to show the lightning overvoltages level using different types of nonlinear surge arresters and then calculations of the lightning protection reliability.

Kuntouttavan työn kehitysmahdollisuudet ja taloudelliset vaikutukset metsäteollisuusyrityksessä

Metsäteollisuudessa henkilöstön keski-ikä on monen muun toimialan tavoin noussut merkittävästi viime vuosina. Samaan aikaan työt ovat monipuolistuneet, ja henkilöstöä on vähennetty kustannustehokkuuden nimissä. Osittain näiden tekijöiden seurauksena sairauspoissaolot ovat nousseet, ja niiden aiheuttamat kustannukset ovat vuosittain hyvin merkittävät. Lisäksi työkyvyttömyys- ja tapaturmaeläköitymisten kustannukset ovat keskimäärin nousseet uuden maksuluokkajärjestelmän käyttöönoton myötä. Sairauspoissaolojen alentamisen ja eläköitymisten ehkäisemiseksi on vuosien varrella hyödynnetty erilaisia käytäntöjä ja toimintamalleja, joiden vaikutusalueet vaihtelevat työturvallisuudesta työhönpaluun tukemiseen. Erilaisia uudelleensijoituksia ja työtehtävien räätälöintejä on mahdollisuuksien mukaan pyritty toteuttamaan, mutta näiden esteenä on pääosin ollut yhteistyön ja tiedon puute, haastava ajankohta, sekä erilaiset negatiiviset asenteet. Kuntouttavalla työllä tarkoitetaan eri osapuolten kanssa yhdessä sovittua, määräaikaista ja normaalista poikkeavaa toimintaa, jolla pyritään vähentämään osatyökykyisen työntekijän pitkiä poissaoloja sekä poistamaan mahdollinen varhaisen eläköitymisen uhka. Tämän tutkimuksen aikana kehitetyn kuntouttavan työn uuden toimintamallin tavoitteena on edelleen lisätä tietoisuutta ja yhteistyötä eri osapuolten välillä sekä vaikuttaa omalta osaltaan työnantajan sairauspoissaolojen ja eläköitymisten aiheuttamiin kustannuksiin.

Active du/dt Filtering for Variable-Speed AC Drives

An oscillating overvoltage has become a common phenomenon at the motor terminal in inverter-fed variable-speed drives. The problem has emerged since modern insulated gate bipolar transistors have become the standard choice as the power switch component in lowvoltage frequency converter drives. Theovervoltage phenomenon is a consequence of the pulse shape of inverter output voltage and impedance mismatches between the inverter, motor cable, and motor. The overvoltages are harmful to the electric motor, and may cause, for instance, insulation failure in the motor. Several methods have been developed to mitigate the problem. However, most of them are based on filtering with lossy passive components, the drawbacks of which are typically their cost and size. In this doctoral dissertation, application of a new active du/dt filtering method based on a low-loss LC circuit and active control to eliminate the motor overvoltages is discussed. The main benefits of the method are the controllability of the output voltage du/dt within certain limits, considerably smaller inductances in the filter circuit resulting in a smaller physical component size, and excellent filtering performance when compared with typical traditional du/dt filtering solutions. Moreover, no additional components are required, since the active control of the filter circuit takes place in the process of the upper-level PWM modulation using the same power switches as the inverter output stage. Further, the active du/dt method will benefit from the development of semiconductor power switch modules, as new technologies and materials emerge, because the method requires additional switching in the output stage of the inverter and generation of narrow voltage pulses. Since additional switching is required in the output stage, additional losses are generated in the inverter as a result of the application of the method. Considerations on the application of the active du/dt filtering method in electric drives are presented together with experimental data in order to verify the potential of the method.

Thermal modelling of semiconductor switches in three-level Neutral Point Clamped Medium Voltage DTC-inverter

The aim of this thesis is to investigate the thermal loading of medium voltage three-level NPC inverter’s semiconductor IGCT switches in different operation points. The objective is to reach both a fairly accurate off-line simulation program and also so simple a simulation model that its implementation into an embedded system could be reasonable in practice and a real time use should become feasible. Active loading limitation of the inverter can be realized with a thermal model which is practical in a real time use. Determining of the component heating has been divided into two parts; defining of component losses and establishing the structure of a thermal network. Basics of both parts are clarified. The simulation environment is Matlab-Simulink. Two different models are constructed – a more accurate one and a simplified one. Potential simplifications are clarified with the help of the first one. Simplifications are included in the latter model and the functionalities of both models are compared. When increasing the calculation time step a decreased number of considered components and time constants of the thermal network can be used in the simplified model. Heating of a switching component is dependent on its topological position and inverter’s operation point. The output frequency of the converter defines mainly which one of the switching components is – because of its losses and heating – the performance limiting component of the converter. Comparison of results given by different thermal models demonstrates that with larger time steps, describing of fast occurring switching losses becomes difficult. Generally articles and papers dealing with this subject are written for two-level inverters. Also inverters which apply direct torque control (DTC) are investigated rarely from the heating point of view. Hence, this thesis completes the former material.

Multilevel converter modulation: implementation and analysis

Multilevel converters provide an attractive solution to bring the benefits of speed-controlled rotational movement to high-power applications. Therefore, multilevel inverters have attracted wide interest in both the academic community and in the industry for the past two decades. In this doctoral thesis, modulation methods suitable especially for series connected H-bridge multilevel inverters are discussed. A concept of duty cycle modulation is presented and its modification is proposed. These methods are compared with other well-known modulation schemes, such as space-vector pulse width modulation and carrier-based modulation schemes. The advantage of the modified duty-cycle modulation is its algorithmic simplicity. A similar mathematical formulation for the original duty cycle modulation is proposed. The modified duty cycle modulation is shown to produce well-formed phase-to-neutral voltages that have lower total harmonic distortion than the space-vector pulse width modulation and the duty cycle modulation. The space-vector-based solution and the duty cycle modulation, on the other hand, result in a better-quality line-to-line voltage and current waveform. The voltage of the DC links in the modules of the series-connected H-bridge inverter are shown to fluctuate while they are under load. The fluctuation causes inaccuracies in the voltage production, which may result in a failure of the flux estimator in the controller. An extension for upper-level modulation schemes, which changes the switching instants of the inverter so that the output voltage meets the reference voltage accurately regardless of the DC link voltages, is proposed. The method is shown to reduce the error to a very low level when a sufficient switching frequency is used. An appropriate way to organize the switching instants of the multilevel inverter is to make only one-level steps at a time. This causes restrictions on the dynamical features of the modulation schemes. The produced voltage vector cannot be rotated several tens of degrees in a single switching period without violating the above-mentioned one-level-step rule. The dynamical capabilities of multilevel inverters are analyzed in this doctoral thesis, and it is shown that the multilevel inverters are capable of operating even in dynamically demanding metal industry applications. In addition to the discussion on modulation schemes, an overvoltage in multilevel converter drives caused by cable reflection is addressed. The voltage reflection phenomenon in drives with long feeder cables causes premature insulation deterioration and also affects the commonmode voltage, which is one of the main reasons for bearing currents. Bearing currents, on the other hand, cause fluting in the bearings, which results in premature bearing failure. The reflection phenomenon is traditionally prevented by filtering, but in this thesis, a modulationbased filterless method to mitigate the overvoltage in multilevel drives is proposed. Moreover, the mitigation method can be implemented as an extension for upper-level modulation schemes. The method exploits the oscillations caused by two consecutive voltage edges so that the sum of the oscillations results in a mitigated peak of the overvoltage. The applicability of the method is verified by simulations together with experiments with a full-scale prototype.

Parallel-Operating Three-Phase Voltage Source Inverters – Circulating CurrentModeling, Analysis and Mitigation

The maximum realizable power throughput of power electronic converters may be limited or constrained by technical or economical considerations. One solution to this problemis to connect several power converter units in parallel. The parallel connection can be used to increase the current carrying capacity of the overall system beyond the ratings of individual power converter units. Thus, it is possible to use several lower-power converter units, produced in large quantities, as building blocks to construct high-power converters in a modular manner. High-power converters realized by using parallel connection are needed for example in multimegawatt wind power generation systems. Parallel connection of power converter units is also required in emerging applications such as photovoltaic and fuel cell power conversion. The parallel operation of power converter units is not, however, problem free. This is because parallel-operating units are subject to overcurrent stresses, which are caused by unequal load current sharing or currents that flow between the units. Commonly, the term ’circulatingcurrent’ is used to describe both the unequal load current sharing and the currents flowing between the units. Circulating currents, again, are caused by component tolerances and asynchronous operation of the parallel units. Parallel-operating units are also subject to stresses caused by unequal thermal stress distribution. Both of these problemscan, nevertheless, be handled with a proper circulating current control. To design an effective circulating current control system, we need information about circulating current dynamics. The dynamics of the circulating currents can be investigated by developing appropriate mathematical models. In this dissertation, circulating current models aredeveloped for two different types of parallel two-level three-phase inverter configurations. Themodels, which are developed for an arbitrary number of parallel units, provide a framework for analyzing circulating current generation mechanisms and developing circulating current control systems. In addition to developing circulating current models, modulation of parallel inverters is considered. It is illustrated that depending on the parallel inverter configuration and the modulation method applied, common-mode circulating currents may be excited as a consequence of the differential-mode circulating current control. To prevent the common-mode circulating currents that are caused by the modulation, a dual modulator method is introduced. The dual modulator basically consists of two independently operating modulators, the outputs of which eventually constitute the switching commands of the inverter. The two independently operating modulators are referred to as primary and secondary modulators. In its intended usage, the same voltage vector is fed to the primary modulators of each parallel unit, and the inputs of the secondary modulators are obtained from the circulating current controllers. To ensure that voltage commands obtained from the circulating current controllers are realizable, it must be guaranteed that the inverter is not driven into saturation by the primary modulator. The inverter saturation can be prevented by limiting the inputs of the primary and secondary modulators. Because of this, also a limitation algorithm is proposed. The operation of both the proposed dual modulator and the limitation algorithm is verified experimentally.

Induction Motor Drive Energy Efficiency - Simulation and Analysis

A coupled system simulator, based on analytical circuit equations and a finite element method (FEM) model of the motor has been developed and it is used to analyse a frequency-converterfed industrial squirrel-cage induction motor. Two control systems that emulate the behaviour of commercial direct-torque-controlled (DTC) and vector-controlled industrial frequency converters have been studied, implemented in the simulation software and verified by extensive laboratory tests. Numerous factors that affect the operation of a variable speed drive (VSD) and its energy efficiency have been investigated, and their significance in the simulation of the VSD results has been studied. The dependency of the frequency converter, induction motor and system losses on the switching frequency is investigated by simulations and measurements at different speeds for both the vector control and the DTC. Intensive laboratory measurements have been carried out to verify the simulation results.

Regulation of B Cell Gene Expression and Function by Ikaros, Helios and Bcl6

B lymphocytes constitute a key branch of adaptive immunity by providing specificity to recognize a vast variety of antigens by B cell antigen receptors (BCR) and secreted antibodies. Antigen recognition activates the cells and can produce antibody secreting plasma cells via germinal center reaction that leads to the maturation of antigen recognition affinity and switching of antibody effector class. The specificity of antigen recognition is achieved through a multistep developmental pathway that is organized by interplay of transcription factors and signals through BCR. Lymphoid malignancies arise from different stages of development in abnormal function of transcriptional regulation. To understand the B cell development and the function of B cells, a thorough understanding of the regulation of gene expression is important. The transcription factors of the Ikaros family and Bcl6 are frequently associated with lymphoma generation. The aim of this study was to reveal the targets of Ikaros, Helios and Bcl6 mediated gene regulation and to find out the function of Ikaros and Helios in B cells. This study uses gene targeted DT40 B cell lines and establishes a role for Ikaros family factors Ikaros and Helios in the regulation of BCR signaling that is important at developmental checkpoints, for cell survival and in activation. Ikaros and Helios had opposing roles in the regulation of BCR signals. Ikaros was found to directly repress the SHIP gene that encodes a signaling lipid-metabolizing enzyme, whereas Helios had activating effect on SHIP expression. The findings demonstrate a balancing function for these two Ikaros family transcription factors in the regulation of BCR signaling as well as in the regulation of gene expression. Bcl6 was found to repress plasma cell gene expression program while maintaining gene expression profile of B cells. Analysis of direct Bcl6 target genes suggested novel mechanisms for Bcl6-mediated suppression of plasma cell differentiation and promoting germinal center phenotype.

Ja vet int va de heter på svenska : interaktion mellan tvåspråkiga elever och deras lärare i en enspråkig klassrumsdiskurs

This is a study about language and learning aspects in the interaction between pupils and teachers in classrooms, where the majority of the pupils are bilingual. The aim of the dissertation is to develop the understanding of interactional learning possibilities and constraints in relation to a bilingual context. Language related learning is used as an overall conception which covers learning related to classroom discourse, language and subject. The empirical study has been made in a Swedish speaking school in a strongly Finnish dominated environment in the south of Finland. In the material, mainly consisting of video recorded lessons in forms one to three, the interaction between the pupils and the teachers is analysed. Building on a social constructionist perspective, where learning is regarded as a social phenomenon, situated and visible in changing participation, sequences where pupils or teachers make the language relevant are emphasised. The sequences are analysed in line with the conversation analytic (CA) approach. A fundamental result is an understanding of a monolingual classroom discourse, jointly constructed by teachers and pupils and visible in the pupils' interactionally problematized code-switching. This means that the pupils are not victims of a top-driven language policy; they are active co-constructors of the monolingual discourse. Through different repair initiations the pupils are doing interactional work in positioning themselves correctly in the monolingual discourse, which they simultaneously maintain. This work has a price in relation to time, knowledge and exactness. The pupils' problematized code-switching is often directly and shortly repaired by the teachers. This kind of repair promotes the pupils' participation and is not, as opposed to the results of research in everyday talk, dispreferred in pupil-teacher talk. When the pupils use the possibility to, in a comparatively easy way, participate and thus express their knowledge through codeswitching, and simultaneously talk a monolingual discourse into being, the teacher can, through direct repair, show an understanding in regard to the content, facilitate language learning and simultaneously confirm the pupils as competent speakers and bilingual individuals. Furthermore, significant results show that the monolingual norm has a function of a contrasting background which gives the pupils and the teachers a possibility to use language alternation as a functional and meaningful activity. The pupils use codeswitching as a way of protesting or expressing non-participation in the classroom talk. By making the pupils' bilingualism relevant, the teachers express understanding and empathy and encourage the pupils' participation in the classroom talk. Bilingualism is a nonpreferred, but functioning, resource in the interaction between pupils and teachers.