Optimization of the power cable for low voltage direct current system

The demand for electricity is constantly growing in contemporary world and, in the same time, quality and reliability requirements are becoming more rigid. In addition, renewable sources of energy have been widely introduced for power generation, and they create specific challenges for the network. Consequently, new solution for distribution system is required, and Low Voltage Direct Current (LVDC) system is the proposed one. This thesis focuses on the investigation of specific cable features for low voltage direct current (LVDC) distribution system. The LVDC system is public ±750 VDC distribution system, which is currently being developed at Lappeen-ranta University of Technology. The aspects, considered in the thesis, are reliable and economic power transmission in distribution networks and possible power line communication in the LVDC cable.

Utilization of a Time Domain Simulator in the Technical and Economic Analysis of a Wind Turbine Electric Drive Train

The amount of installed wind power has been growing exponentially during the past ten years. As wind turbines have become a significant source of electrical energy, the interactions between the turbines and the electric power network need to be studied more thoroughly than before. Especially, the behavior of the turbines in fault situations is of prime importance; simply disconnecting all wind turbines from the network during a voltage drop is no longer acceptable, since this would contribute to a total network collapse. These requirements have been a contributor to the increased role of simulations in the study and design of the electric drive train of a wind turbine. When planning a wind power investment, the selection of the site and the turbine are crucial for the economic feasibility of the installation. Economic feasibility, on the other hand, is the factor that determines whether or not investment in wind power will continue, contributing to green electricity production and reduction of emissions. In the selection of the installation site and the turbine (siting and site matching), the properties of the electric drive train of the planned turbine have so far been generally not been taken into account. Additionally, although the loss minimization of some of the individual components of the drive train has been studied, the drive train as a whole has received less attention. Furthermore, as a wind turbine will typically operate at a power level lower than the nominal most of the time, efficiency analysis in the nominal operating point is not sufficient. This doctoral dissertation attempts to combine the two aforementioned areas of interest by studying the applicability of time domain simulations in the analysis of the economicfeasibility of a wind turbine. The utilization of a general-purpose time domain simulator, otherwise applied to the study of network interactions and control systems, in the economic analysis of the wind energy conversion system is studied. The main benefits of the simulation-based method over traditional methods based on analytic calculation of losses include the ability to reuse and recombine existing models, the ability to analyze interactions between the components and subsystems in the electric drive train (something which is impossible when considering different subsystems as independent blocks, as is commonly done in theanalytical calculation of efficiencies), the ability to analyze in a rather straightforward manner the effect of selections other than physical components, for example control algorithms, and the ability to verify assumptions of the effects of a particular design change on the efficiency of the whole system. Based on the work, it can be concluded that differences between two configurations can be seen in the economic performance with only minor modifications to the simulation models used in the network interaction and control method study. This eliminates the need ofdeveloping analytic expressions for losses and enables the study of the system as a whole instead of modeling it as series connection of independent blocks with no lossinterdependencies. Three example cases (site matching, component selection, control principle selection) are provided to illustrate the usage of the approach and analyze its performance.

Source and Target Text-Orientation in Drama Translation. An Analysis of Four Translations of William Shakespeare’s Julius Caesar

Tässä pro gradu -tutkielmassa käsittelen lähde- ja kohdetekstikeskeisyyttä näytelmäkääntämisessä. Tutkimuskohteina olivat käännösten sanasto, syntaksi, näyttämötekniikka, kielikuvat, sanaleikit, runomitta ja tyyli. Tutkimuksen tarkoituksena oli selvittää, näkyykö teoreettinen painopisteen siirtyminen lähdetekstikeskeisyydestä kohdetekstikeskeisyyteen suomenkielisessä näytelmäkääntämisessä. Oletuksena oli, että siirtyminen näkyy käytetyissä käännösstrategioissa. Tutkimuksen teoriaosuudessa käsitellään ensin lähde- ja kohdetekstikeskeisiä käännösteorioita. Ensin esitellään kaksi lähdetekstikeskeistä teoriaa, jotka ovat Catfordin (1965) muodollinen vastaavuus ja Nidan (1964) dynaaminen ekvivalenssi. Kohdetekstikeskeisistä teorioista käsitellään Touryn (1980) ja Newmarkin (1981) teoreettisia näkemyksiä sekä Reiss ja Vermeerin (1986) esittelemää skopos-teoriaa. Vieraannuttamisen ja kotouttamisen periaatteet esitellään lyhyesti. Teoriaosuudessa käsitellään myös näytelmäkääntämistä, William Shakespearen kieltä ja siihen liittyviä käännösongelmia. Lisäksi esittelen lyhyesti Shakespearen kääntämistä Suomessa ja Julius Caesarin neljä kääntäjää. Tutkimuksen materiaalina oli neljä Shakespearen Julius Caesar –näytelmän suomennosta, joista Paavo Cajanderin käännös on julkaistu vuonna 1883, Eeva-Liisa Mannerin vuonna 1983, Lauri Siparin vuonna 2006 ja Jarkko Laineen vuonna 2007. Analyysissa käännöksiä verrattiin lähdetekstiin ja toisiinsa ja vertailtiin kääntäjien tekemiä käännösratkaisuja. Tulokset olivat oletuksen mukaisia. Lähdetekstikeskeisiä käännösstrategioita oli käytetty uusissa käännöksissä vähemmän kuin vanhemmissa. Kohdetekstikeskeiset strategiat erosivat huomattavasti toisistaan ja uusinta käännöstä voi sanoa adaptaatioksi. Jatkotutkimuksissa tulisi materiaali laajentaa koskemaan muitakin Shakespearen näytelmien suomennoksia. Eri aikakausien käännöksiä tulisi verrata keskenään ja toisiinsa, jotta voitaisiin luotettavasti kuvata muutosta lähde- ja kohdetekstikeskeisten käännösstrategioiden käytössä ja eri aikakausien tyypillisten strategioiden kartoittamiseksi.

Vertailu kahden erityyppisen virtasyötetyn hakkurin soveltuvuudesta polttokennokäyttöihin

Concerns about condition of the environment and rising fossil fuel prices have accelerated the research of finding new cheap and environmental friendly energy source. Fuel cells are one of the most promising green technologies, especially in the field of distributed energy generation, backup power systems, transportation and mobile power generation. In this bachelor’s thesis use of fuel cells is studied, especially from the DC-DC converter point of view. This bachelor’s thesis concentrates on study of two different DC-DC converters. The aim of this thesis is to study design and steering methods for proposed converters. The ultimate aim of this thesis is to determine which one of proposed converters is most suitable for fuel cell applications.

Mathematical equation correction to spectral and transport interferences in high-resolution continuum source flame atomic absorption spectrometry: determination of lead in phosphoric acid

In this work, a new mathematical equation correction approach for overcoming spectral and transport interferences was proposed. The proposal was applied to eliminate spectral interference caused by PO molecules at the 217.0005 nm Pb line, and the transport interference caused by variations in phosphoric acid concentrations. Correction may be necessary at 217.0005 nm to account for the contribution of PO, since Atotal217.0005 nm = A Pb217.0005 nm + A PO217.0005 nm. This may be easily done by measuring other PO wavelengths (e.g. 217.0458 nm) and calculating the relative contribution of PO absorbance (A PO) to the total absorbance (Atotal) at 217.0005 nm: A Pb217.0005 nm = Atotal217.0005 nm - A PO217.0005 nm = Atotal217.0005 nm - k (A PO217.0458 nm). The correction factor k is calculated from slopes of calibration curves built up for phosphorous (P) standard solutions measured at 217.0005 and 217.0458 nm, i.e. k = (slope217.0005 nm/slope217.0458 nm). For wavelength integrated absorbance of 3 pixels, sample aspiration rate of 5.0 ml min-1, analytical curves in the 0.1 - 1.0 mg L-1 Pb range with linearity better than 0.9990 were consistently obtained. Calibration curves for P at 217.0005 and 217.0458 nm with linearity better than 0.998 were obtained. Relative standard deviations (RSD) of measurements (n = 12) in the range of 1.4 - 4.3% and 2.0 - 6.0% without and with mathematical equation correction approach were obtained respectively. The limit of detection calculated to analytical line at 217.0005 nm was 10 µg L-1 Pb. Recoveries for Pb spikes were in the 97.5 - 100% and 105 - 230% intervals with and without mathematical equation correction approach, respectively.

Determination of copper at wide range concentrations using instrumental features of high-resolution continuum source flame atomic absorption spectrometry

This work describes a method to determine Cu at wide range concentrations in a single run without need of further dilutions employing high-resolution continuum source flame atomic absorption spectrometry. Different atomic lines for Cu at 324.754 nm, 327.396 nm, 222.570 nm, 249.215 nm and 224.426 nm were evaluated and main figures of merit established. Absorbance measurements at 324.754 nm, 249.215 nm and 224.426 nm allows the determination of Cu in the 0.07 - 5.0 mg L-1, 5.0 - 100 mg L-1 and 100 - 800 mg L-1 concentration intervals respectively with linear correlation coefficients better than 0.998. Limits of detection were 21 µg L-1, 310 µg L-1 and 1400 µg L-1 for 324.754 nm, 249.215 nm and 224.426 nm, respectively and relative standard deviations (n = 12) were £ 2.7%. The proposed method was applied to water samples spiked with Cu and the results were in agreement at a 95% of confidence level (paired t-test) with those obtained by line-source flame atomic absorption spectrometry.

Akkujen ja superkondensaattorien yhteiskäyttö energiavarastoina ja niiden verkkoon liittäminen ajoneuvoissa

Ajoneuvojen tiukentuneet päästörajoitukset, sekä ajoneuvojen kokonaishyötysuhteen parantamisen tarve ohjaavat ajoneuvovalmistajia kehittämään uusia ratkaisuja. Energiavarastojen käyttö ajoneuvoissa on yleistynyt ja niiden käytöllä voidaan saada huomattava energiasäästö. Tässä kandidaatintyössä on esitelty erilaisia energiavarastoja ja niiden verkkoon liittämistä. Pääpaino työssä on akkujen ja superkondensaattorien rinnankytkennässä. Energiavarastot pyritään kytkemään mahdollisimman vähällä tehoelektroniikalla verkkoon. Esimerkkitapaukseksi on otettu litium-ioni akkujen ja superkondensaattorien rinnankytkentä vaihtojännitteeseen pelkällä invertterillä.

Insulation System in an Integrated Motor Compressor

A high-speed and high-voltage solid-rotor induction machine provides beneficial features for natural gas compressor technology. The mechanical robustness of the machine enables its use in an integrated motor-compressor. The technology uses a centrifugal compressor, which is mounted on the same shaft with the high-speed electrical machine driving it. No gearbox is needed as the speed is determined by the frequency converter. The cooling is provided by the process gas, which flows through the motor and is capable of transferring the heat away from the motor. The technology has been used in the compressors in the natural gas supply chain in the central Europe. New areas of application include natural gas compressors working at the wellheads of the subsea gas reservoir. A key challenge for the design of such a motor is the resistance of the stator insulation to the raw natural gas from the well. The gas contains water and heavy hydrocarbon compounds and it is far harsher than the sales gas in the natural gas supply network. The objective of this doctoral thesis is to discuss the resistance of the insulation to the raw natural gas and the phenomena degrading the insulation. The presence of partial discharges is analyzed in this doctoral dissertation. The breakdown voltage of the gas is measured as a function of pressure and gap distance. The partial discharge activity is measured on small samples representing the windings of the machine. The electrical field behavior is also modeled by finite element methods. Based on the measurements it has been concluded that the discharges are expected to disappear at gas pressures above 4 – 5 bar. The disappearance of discharges is caused by the breakdown strength of the gas, which increases as the pressure increases. Based on the finite element analysis, the physical length of a discharge seen in the PD measurements at atmospheric pressure was approximated to be 40 – 120 m. The chemical aging of the insulation when exposed to raw natural gas is discussed based on a vast set of experimental tests with the gas mixture representing the real gas mixture at the wellhead. The mixture was created by mixing dry hydrocarbon gas, heavy hydrocarbon compounds, monoethylene glycol, and water. The mixture was chosen to be more aggressive by increasing the amount of liquid substances. Furthermore, the temperature and pressure were increased, which resulted in accelerated test conditions. The time required to detect severe degradation was thus decreased. The test program included a comparison of materials, an analysis of the e ects of di erent compounds in the gas mixture, namely water and heavy hydrocarbons, on the aging, an analysis of the e ects of temperature and exposure duration, and also an analysis on the e ect of sudden pressure changes on the degradation of the insulating materials. It was found in the tests that an insulation consisting of mica, glass, and epoxy resin can tolerate the raw natural gas, but it experiences some degradation. The key material in the composite insulation is the resin, which largely defines the performance of the insulation system. The degradation of the insulation is mostly determined by the amount of gas mixture di used into it. The di usion was seen to follow Fick’s second law, but the coe cients were not accurately defined. The di usion was not sensitive to temperature, but it was dependent upon the thermodynamic state of the gas mixture, in other words, the amounts of liquid components in the gas. The weight increase observed was mostly related to heavy hydrocarbon compounds, which act as plasticizers in the epoxy resin. The di usion of these compounds is determined by the crosslink density of the resin. Water causes slight changes in the chemical structure, but these changes do not significantly contribute to the aging phenomena. Sudden changes in pressure can lead to severe damages in the insulation, because the motion of the di used gas is able to create internal cracks in the insulation. Therefore, the di usion only reduces the mechanical strength of the insulation, but the ultimate breakdown can potentially be caused by a sudden drop in the pressure of the process gas.

Soluble tissue sugar content and leaf blast severity in response to the application of calcinated serpentinite as a silicon source in irrigated rice

A field experiment conducted with the irrigated rice cultivar BRS Formoso, to assess the efficiency of calcinated serpentinite as a silicon source on grain yield was utilized to study its effect on leaf blast severity and tissue sugar levels. The treatments consisted of five rates of calcinated serpentinite (0, 2, 4, 6, 8 Mg.ha-1) incorporated into the soil prior to planting. The leaf blast severity was reduced at the rate of 2.96% per ton of calcinated serpentinite. The total tissue sugar content decreased significantly as the rates of serpentinite applied increased (R² = 0.83). The relationship between the tissue sugar content and leaf blast severity was linear and positive (R² = 0.81). The decrease in leaf blast severity with increased rates of calcinated serpentinite was also linear (R²= 0.96) and can be ascribed to reduced sugar level.

Decomposition of corn and soybean residues under field conditions and their role as inoculum source

Necrotrophic parasites of above-ground plant parts survive saprophytically, between growing seasons in host crop residues. In an experiment conducted under field conditions, the time required in months for corn and soybean residues to be completely decomposed was quantified. Residues were laid on the soil surface to simulate no-till farming. Crop debris of the two plant species collected on the harvesting day cut into pieces of 5.0cm-long and a 200g mass was added to nylon mesh bags. At monthly intervals, bags were taken to the laboratory for weighing. Corn residues were decomposed within 37.0 months and those of soybean, within 34.5 months. Hw main necrotrophic fungi diagnosed in the corn residues were Colletotrichum gramicola, Diplodia spp. and Gibberella zeae, and those in soybeans residues were Cercospora kikuchii, Colletotrichum spp, Glomerella sp. and Phomopsis spp. Thus, those periods shoulb be observed in crop rotation aimed at to eliminating contaminated residues and, consequently, the inoculum from the cultivated area.

Diskreettiaikainen liukuvan moodin säätö kiinteäoksidipolttokennon DC-tasonnostossa

Huoli ympäristön tilasta ja fossiilisten polttoaineiden hinnan nousu ovat vauhdittaneet tutkimusta uusien energialähteiden löytämiseksi. Polttokennot ovat yksi lupaavimmista tekniikoista etenkin hajautetun energiantuotannon, varavoimalaitosten sekä liikennevälineiden alueella. Polttokenno on tehonlähteenä kuitenkin hyvin epäideaalinen, ja se asettaa tehoelektroniikalle lukuisia erityisvaatimuksia. Polttokennon kytkeminen sähköverkkoon on tavallisesti toteutettu käyttämällä galvaanisesti erottavaa DC/DC hakkuria sekä vaihtosuuntaajaa sarjassa. Polttokennon kulumisen estämiseksi tehoelektroniikalta vaaditaan tarkkaa polttokennon lähtövirran hallintaa. Perinteisesti virran hallinta on toteutettu säätämällä hakkurin tulovirtaa PI (Proportional and Integral) tai PID (Proportional, Integral and Derivative) -säätimellä. Hakkurin epälineaarisuudesta johtuen tällainen ratkaisu ei välttämättä toimi kaukana linearisointipisteestä. Lisäksi perinteiset säätimet ovat herkkiä mallinnusvirheille. Tässä diplomityössä on esitetty polttokennon jännitettä nostavan hakkurin tilayhtälökeskiarvoistusmenetelmään perustuva malli, sekä malliin perustuva diskreettiaikainen integroiva liukuvan moodin säätö. Esitetty säätö on luonteeltaan epälineaarinen ja se soveltuu epälineaaristen ja heikosti tunnettujen järjestelmien säätämiseen.

Monitoring of centrifugal pump operation by a frequency converter

Centrifugal pumps are widely used in industrial and municipal applications, and they are an important end-use application of electric energy. However, in many cases centrifugal pumps operate with a significantly lower energy efficiency than they actually could, which typically has an increasing effect on the pump energy consumption and the resulting energy costs. Typical reasons for this are the incorrect dimensioning of the pumping system components and inefficiency of the applied pump control method. Besides the increase in energy costs, an inefficient operation may increase the risk of a pump failure and thereby the maintenance costs. In the worst case, a pump failure may lead to a process shutdown accruing additional costs. Nowadays, centrifugal pumps are often controlled by adjusting their rotational speed, which affects the resulting flow rate and output pressure of the pumped fluid. Typically, the speed control is realised with a frequency converter that allows the control of the rotational speed of an induction motor. Since a frequency converter can estimate the motor rotational speed and shaft torque without external measurement sensors on the motor shaft, it also allows the development and use of sensorless methods for the estimation of the pump operation. Still today, the monitoring of pump operation is based on additional measurements and visual check-ups, which may not be applicable to determine the energy efficiency of the pump operation. This doctoral thesis concentrates on the methods that allow the use of a frequency converter as a monitoring and analysis device for a centrifugal pump. Firstly, the determination of energy-efficiency- and reliability-based limits for the recommendable operating region of a variable-speed-driven centrifugal pump is discussed with a case study for the laboratory pumping system. Then, three model-based estimation methods for the pump operating location are studied, and their accuracy is determined by laboratory tests. In addition, a novel method to detect the occurrence of cavitation or flow recirculation in a centrifugal pump by a frequency converter is introduced. Its sensitivity compared with known cavitation detection methods is evaluated, and its applicability is verified by laboratory measurements for three different pumps and by using two different frequency converters. The main focus of this thesis is on the radial flow end-suction centrifugal pumps, but the studied methods can also be feasible with mixed and axial flow centrifugal pumps, if allowed by their characteristics.

Vuotasapainon hallinta kokosiltasyötetyssä muuntajassa

Keskitaajuudella toimivia muuntajia käytetään laajalti tehoelektroniikkasovelluksissa kuten DC/DC-konverttereissa ja muissa hakkuriteholähteissä. Muuntaja on induktiivinen komponentti, jonka magneettisen tasapainon säilyttäminen hakkuriteholähteissä on laitteen virheettömän toiminnan kannalta tärkeää. Muuntajaa syöttävän virtapiirin on muodostettava symmetrinen syöttöjännite, jotta muuntajan vuo ei ajaudu positiiviseen tai negatiiviseen kyllästykseen. Tässä diplomityössä esitetään muuntajan sähkömagneettinen toimintaperiaate, kyllästymisen syyt hakkuriteholähteissä sekä kehitetään aktiivinen ohjaus vuotasapainon säilyttämiseksi. Hakkuriteholähteissä käytettävissä muuntajissa on monesti useampi kuin kaksi käämiä. Tässä työssä tutkittavassa muuntajassa on useita ensiöitä ja useita toisioita ja muuntajaa syötetään keskitaajuudella. Tämä tuo uusia ongelmia verrattuna perinteiseen yksivaiheiseen DC/DC-konvertteriin. Näihin ongelmiin esitetään ratkaisut diplomityön tutkimuksessa.

Switching components for medium voltage drives

Nowadays power drives are the essential part almost of all technological processes. Improvement of efficiency and reduction of losses require development of semiconductor switches. It has a particular meaning for the constantly growing market of renewable sources, especially for wind turbines, which demand more powerful semiconductor devices for control with growth of power. Also at present semiconductor switches are the key component in energy transmission, optimization of generation and network connection. The aim of this thesis is to make a survey of contemporary semiconductor components, showing difference in structures, advantages, disadvantages and most suitable applications. There is topical information about voltage, frequency and current limits of different switches. Study tries to compare dimensions and price of different components. Main manufacturers of semiconductor components are presented with the review of devices produced by them, and a conclusion about their availability was made. IGBT is selected as a main component in this study, because nowadays it is the most attractive component for usage in power drives, especially at the low levels of medium voltage. History of development of IGBT structure, static and dynamic characteristics are considered. Thesis tells about assemblies and connection of components and problems which can appear. One of key questions about semiconductor materials and their future development was considered. For the purpose of comparison strong and weak sides of different switches, calculation of losses of IGBT and its basic competitor – IGCT is presented. This master’s thesis makes an effort to answer the question if there are at present possibilities of accurate selection of switches for electrical drives of different rates of power and looks at future possible ways of development of semiconductor market.

Galvaanisen erotuksen toteuttaminen tasavirtasähkönjakelun asiakaspäätelaitteessa

Suomessa sähkönjakeluverkon pääasialliset jännitetasot ovat 20 kV ja 400 V. 20 kV jännitetasolla sähkö viedään lähelle kuluttajia ja muunnetaan pienemmäksi lähellä asiakkaita. Haittapuolena on se, että 20 kV avojohtosähkönsiirtoverkko on hyvin vika-altis ja usein yhden haaran vikaantuessa monta muutakin jää ilman sähköä. Lisäksi hintavien ja suurien jakelumuuntajien määrä on suuri. Vaihtoehtona on toteuttaa osa sähkönjakelusta tasajännitteellä, jolloin tehollinen pienjännite olisi 400 V:a suurempi. Tällöin sähköä voitaisiin siirtää pidempiä matkoja ilman, että asiakaskohtaisia tai muutaman asiakkaan kattavia 20 kV siirtolinjoja tarvitsisi käyttää. Tämä edellyttää vaihtosuuntauksen toteuttamista kuluttajan päässä. Tässä työssä esiteltävällä 1 kVA:n tehoisella vaihtosuuntaajalla muodostetaan tasasähköjakeluverkosta saatavasta 750 V tasasähköstä yksivaiheista (230 VRMS, 50 Hz) verkkojännitettä. Laite on suunniteltu toteuttamaan galvaaninen erotus mahdollisimman hyvällä hyötysuhteella. Suurtaajuusmuuntajan mitoitus mahdollisimman hyvälle hyötysuhteelle on haastava tehtävä, koska vaatimuksia sille asettavat sekä syöttävä resonanssikonvertteri että syötettävä syklokonvertteri. Mitoituksessa on pyrittävä löytämään mahdollisimman hyvä hyötysuhde kustannusten ja toteutettavuuden suhteen.