Spectral analysis of the angular distribution function of back reflectors for thin film silicon solar cells

Nowadays, one of the most important challenges to enhance the efficiency of thin film silicon solar cells is to increase the short circuit intensity by means of optical confinement methods, such as textured back-reflector structures. In this work, two possible textured structures to be used as back reflectors for n-i-p solar cells have been optically analyzed and compared to a smooth one by using a system which is able to measure the angular distribution function (ADF) of the scattered light in a wide spectral range (350-1000 nm). The accurate analysis of the ADF data corresponding to the reflector structures and to the μc-Si:H films deposited onto them allows the optical losses due to the reflector absorption and its effectiveness in increasing light absorption in the μc-Si:H layer, mainly at long wavelengths, to be quantified.

IGBT:N KYLLÄSTYSVALVONTA

Tässä työssä on tutkittu IGBT-modulin kyllästysvalvontaa. Periaatteellisena erona yleisesti käytössä olevaan IGBT:n kyllästysvalvontamenetelmään on valvonnan perustuminen IGBT-modulin läpi kulkevaan virtaan, sen yli olevan jännitteen mittaamisen asemesta. IGBT-modulin läpi kulkeva virta aiheuttaa pienen jännitehäviön IGBT-modulin sisällä olevassa DC-miinuskiskossa. Jännitehäviön suuruus riippuu modulin läpi kulkevan virran suuruudesta. Jännitehäviö voidaan mitata kahden mittapisteen välisenä jännite-erona. Kun jännite-ero mittapisteiden välillä kasvaa tarpeeksi suureksi, IGBT:n voidaan olettaa olevan oikosulussa ja laukaisu voidaan suorittaa. Kyllästystilan havaitsemista kuitenkin vaikeuttaa se, että kyseisen DC-miinuskiskon läpi kulkee moottorivirta. Moottorivirran aiheuttamat jännite-erot on pystyttävä erottamaan luotettavasti oikosulkutilanteesta. Lisäksi komponentin ylikuormitettavuusvaatimukset lisäävät kytkennän toteuttamisen vaikeutta. Komponenttia voidaan hetkellisesti ylikuormittaa moninkertaisella nimellisvirralla eikä tämäkään tilanne saa johtaa laukaisuun.Kyllästysvalvonta toteutetaan taajuusmuuttajaan, joka on tunnetusti varsin häiriöinen ympäristö. DC-miinuskiskon mittapisteiden välissä on tämän johdosta havaittavissa virrasta riippuvan jännite-eron lisäksi erittäin voimakkaita kytkentäilmiöistä johtuvia häiriöitä. Myös muiden IGBT-modulien kytkentäilmiöistä johtuvat häiriöt kytkeytyvät kyllästysvalvontakytkentään ja vaikeuttavat osaltaan sen toteuttamista.

Monitoisioisen muuntajan parametrien mittaus

Tässä kandidaatintyössä on tarkoitus määrittää monitoisioisen muuntajan yksivaiheisen sijaiskytkentä ja sen parametrit käyttämällä perinteisiä mittausmenetelmiä. Näihin kuuluvat tyhjäkäynti-, oikosulku- sekä tasajännitekoe. Muuntajasta on tehty simulointimalli, jota varten sijaiskytkennän parametreja tarvitaan.

Vaasan Sähköverkko Oy:n keskijänniteverkon nykytilan määritys sekä kehittämissuunnitelma käyttövarmuuden näkökulmasta

Tämän työn tavoitteena on analysoida Vaasan Sähköverkko Oy:n keskijänniteverkon nykytila sekä selvittää verkon kehittämisen suuntaviivoja. Nykytilan määrityksessä selvitetään kuormitettavuusasteet, jännitteenalenemat, häviöt oiko- ja maasulkusuojauksen toimivuus sekä keskeytyskustannukset. Nykytilan määrityksen apuna käytettiin verkkotietojärjestelmä Xpowerin tehojako-, oikosulku- ja maasulkulaskentoja. Nykytila on määritetty sekä normaalissa kytkentätilanteessa, että tilanteessa jossa yksi sähköasema kerrallaan on poissa käytöstä. Nykytilan määrityksen perusteella voidaan todeta, että normaalissa kytkentätilanteessa keskijänniteverkko täyttää suurilta osin sille asetetut tekniset reunaehdot, jotka ovat jännitteenalenema, kuormitettavuus, oikosulkukestoisuus sekä oiko- ja maasulkusuojauksen havahtuvaisuus. Jotta reunaehdot toteutuisivat kokonaisuudessaan, tulee oikosulkukestottomien lähtöjen releasetteluja muuttaa tai vaihtaa oikosulkukestottomat johto-osuudet suurempi poikkipintaiseen johtimeen. Nykytilan määrityksen perusteella neljän päämuuntajan kuormitettavuusaste on yli 90 %, joten näiden asemien alueiden kehitystä tulee tarkkailla. Sähköasemien korvaustarkastelun perusteella viiden sähköaseman korvaus tuottaa ongelmia jo nykyisillä huippukuormilla. Työssä tehtyjen selvitystöiden perusteella Vaasan Sähköverkko Oy:n keskijänniteverkkoon lisättiin 10 maastokatkaisijaa sekä selvitettiin verkon mahdollisia tulevaisuuden kehittämisen suuntaviivoja.

Estimation of existing cable systems in generator-busbar unit and choice the optimal solution for its modernization

The aim of this master’s thesis is to develop an algorithm to calculate the cable network for heat and power station CHGRES. This algorithm includes important aspect which has an influence on the cable network reliability. Moreover, according to developed algorithm, the optimal solution for modernization cable system from economical and technical point of view was obtained. The conditions of existing cable lines show that replacement is necessary. Otherwise, the fault situation would happen. In this case company would loss not only money but also its prestige. As a solution, XLPE single core cables are more profitable than other types of cable considered in this work. Moreover, it is presented the dependence of value of short circuit current on number of 10/110 kV transformers connected in parallel between main grid and considered 10 kV busbar and how it affects on final decision. Furthermore, the losses of company in power (capacity) market due to fault situation are presented. These losses are commensurable with investment to replace existing cable system.

Heating control of an electrical motor

Electrical motors on a ship attackable to different factors which decrease these lifetimes. One of the main external factors on a ship which usually is a reason of the motor failure is a moisture condensation which decreases the motor winding insulation and increase a probability of the short circuit. Therefore, the protection against moisture is necessary for ship electrical motors. The motor should be protected against moisture all time when it does not operate. The necessity of such protection requires a lot of energy consumption. This master’s thesis is focused on the creation of the electrical motor thermal model and on the different methods of the motor protection against moisture analysis with energy consumption point of view.

Advanced orbital pipe welding

Since the introduction of automatic orbital welding in pipeline application in 1961, significant improvements have been obtained in orbital pipe welding systems. Requirement of more productive welding systems for pipeline application forces manufacturers to innovate new advanced systems and welding processes for orbital welding method. Various methods have been used to make welding process adaptive, such as visual sensing, passive visual sensing, real-time intelligent control, scan welding technique, multi laser vision sensor, thermal scanning, adaptive image processing, neural network model, machine vision, and optical sensing. Numerous studies are reviewed and discussed in this Master’s thesis and based on a wide range of experiments which already have been accomplished by different researches the vision sensor are reported to be the best choice for adaptive orbital pipe welding system. Also, in this study the most welding processes as well as the most pipe variations welded by orbital welding systems mainly for oil and gas pipeline applications are explained. The welding results show that Gas Metal Arc Welding (GMAW) and its variants like Surface Tension Transfer (STT) and modified short circuit are the most preferred processes in the welding of root pass and can be replaced to the Gas Tungsten Arc Welding (GTAW) in many applications. Furthermore, dual-tandem gas metal arc welding technique is currently considered the most efficient method in the welding of fill pass. Orbital GTAW process mostly is applied for applications ranging from single run welding of thin walled stainless tubes to multi run welding of thick walled pipes. Flux cored arc welding process is faster process with higher deposition rate and recently this process is getting more popular in pipe welding applications. Also, combination of gas metal arc welding and Nd:YAG laser has shown acceptable results in girth welding of land pipelines for oil and gas industry. This Master’s thesis can be implemented as a guideline in welding of pipes and tubes to achieve higher quality and efficiency. Also, this research can be used as a base material for future investigations to supplement present finding.

Jännitevälipiiritaajuusmuuttajan moottorikaapelin maksimipituuden määrittely

Työssä tutkitaan, kuinka pitkää moottorikaapelia on jännitevälipiiritaajuusmuuttajan kanssa mahdollista käyttää niin, että määritellyt reunaehdot vielä toteutuvat. Tavoitteena on tuottaa tietoa myynnille, markkinoinnille, tuotehallinnalle sekä tuoteylläpidolle siitä, miten taajuus-muuttaja toimii pidemmillä moottorikaapeleilla kuin valmistaja suosittelee. Tutkitut moottori-kaapelipituudet olivat 175…1025 metriä ja tutkitut laitteet nimellislähtövirroiltaan 2,4...25 A. Työssä aihetta käsitellään jänniteheijastusten näkökulmasta. Lisäksi tutkitaan moottorikaapelin pituuden vaikutusta taajuusmuuttajan eri komponenttien lämpenemiseen. Taajuusmuuttajan toiminnallisuutta arvioidaan moottorin suunnanvaihtojen avulla sekä turvallista toimintaa oikosulkutestein. Tutkittujen taajuusmuuttajien kohdalla on mahdollista käyttää taajuusmuuttajavalmistajan suositusta pidempiä moottorikaapeleita. Moottoriliittimien ylijännitteitä aiheuttavat jännite-heijastukset eivät aiheuttaneet raja-arvoja ylittäviä huippujännitteitä tutkituilla laitekokoon-panoilla. Myös lämpötilannousu oli maltillista tai jopa vähäistä taajuusmuuttajasta mitatuilla komponenteilla. Moottorisäätö havaittiin toimintakykyiseksi pidemmilläkin moottorikaape-leilla, tosin moottorin vääntömomentti heikkeni moottorikaapelien pituutta kasvatettaessa. Virranmittaus toimi hyvin myös pitkillä kaapeleilla, tuottaen vikalaukaisun kaikissa tehdyissä oikosulkutilanteissa. Moottorin ja taajuusmuuttajan melutaso nousivat moottorikaapelien pi-tuutta kasvatettaessa, vaikkakin moottorin käynti oli tasaista ja katkotonta Moottorikaapelin pituutta voidaan kasvattaa 325 metriin kaikissa tutkituissa laitteissa ilman, että mikään tutkittu ominaisuus vielä olennaisesti heikkenisi. Vielä 525 metrin moottorikaape-leita on mahdollista käyttää, mutta tällöin vääntömomentin tuotto on jo heikompaa.

Methodology for Photovoltaic Modules Characterization and Shading Effects Analysis

This work describes the methodology, basic procedures and instrumental employed by the Solar Energy Laboratory at Universidade Federal do Rio Grande do Sul for the determination of current-voltage characteristic curves of photovoltaic modules. According to this methodology, I-V characteristic curves were acquired for several modules under diverse conditions. The main electrical parameters were determined and the temperature and irradiance influence on photovoltaic modules performance was quantified. It was observed that most of the tested modules presented output power values considerably lower than those specified by the manufacturers. The described hardware allows the testing of modules with open-circuit voltage up to 50 V and short-circuit current up to 8 A.

Changes in the electrophysiological parameters of the posterior intestine of Anguilla anguilla (Pisces) induced by oxytocin, urotensin II and aldosterone

In view of the importance of the intestine in the osmoregulation of freshwater fishes, we determined the effects of oxytocin, urotensin II (UII), and aldosterone added to the serosal side of the isolated posterior intestine of the freshwater-adapted teleost Anguilla anguilla on electrophysiological parameters. Oxytocin decreased the short-circuit current (SCC) and transepithelial potential difference (TPD) at concentrations of 1 and 10 mU/ml (to 50% and 42% of control values, respectively), but did not alter these parameters at a concentration of 0.1 mU/ml. UII reduced SCC and TPD at concentrations of 10 nM, 50 nM and 100 nM (to 85% of control values), but increased these parameters at the concentration of 500 nM (to 115% of control values). Aldosterone did not alter SCC or TPD at the concentrations tested (10 nM and 100 nM). Oxytocin may open Na+ channels in the apical membrane, allowing the flow of Na+ to the serosa, reducing SCC and TPD. Should this hypothesis be correct, oxytocin would be important for freshwater adaptation, since it would increase Na+ absorption. The reduction of SCC and TPD in the posterior intestine of A. anguilla induced by UII is evidence that this neurohormone is also important for freshwater adaptation in teleosts. Aldosterone did not show this effect probably due to the lack of receptors in this organ

The Shiga toxin 2 B subunit inhibits net fluid absorption in human colon and elicits fluid accumulation in rat colon loops

Shiga toxin (Stx)-producing Escherichia coli (STEC) colonizes the large intestine causing a spectrum of disorders, including watery diarrhea, bloody diarrhea (hemorrhagic colitis), and hemolytic-uremic syndrome. It is estimated that hemolytic-uremic syndrome is the most common cause of acute renal failure in infants in Argentina. Stx is a multimeric toxin composed of one A subunit and five B subunits. In this study we demonstrate that the Stx2 B subunit inhibits the water absorption (Jw) across the human and rat colonic mucosa without altering the electrical parameters measured as transepithelial potential difference and short circuit current. The time-course Jw inhibition by 400 ng/ml purified Stx2 B subunit was similar to that obtained using 12 ng/ml Stx2 holotoxin suggesting that both, A and B subunits of Stx2 contributed to inhibit the Jw. Moreover, non-hemorrhagic fluid accumulation was observed in rat colon loops after 16 h of treatment with 3 and 30 ng/ml Stx2 B subunit. These changes indicate that Stx2 B subunit induces fluid accumulation independently of A subunit activity by altering the usual balance of intestinal absorption and secretion toward net secretion. In conclusion, our results suggest that the Stx2 B subunit, which is non-toxic for Vero cells, may contribute to the watery diarrhea observed in STEC infection. Further studies will be necessary to determine whether the toxicity of Stx2 B subunit may have pathogenic consequences when it is used as a component in an acellular STEC vaccine or as a vector in cancer vaccines.

Electrical parameters and water permeability properties of monolayers formed by T84 cells cultured on permeable supports

T84 is an established cell line expressing an enterocyte phenotype whose permeability properties have been widely explored. Osmotic permeability (P OSM), hydraulic permeability (P HYDR) and transport-associated net water fluxes (J W-transp), as well as short-circuit current (I SC), transepithelial resistance (R T), and potential difference (deltaV T) were measured in T84 monolayers with the following results: P OSM 1.3 ± 0.1 cm.s-1 x 10-3; P HYDR 0.27 ± 0.02 cm.s-1; R T 2426 ± 109 omega.cm², and deltaV T 1.31 ± 0.38 mV. The effect of 50 µM 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (DCEBIO), a "net Cl- secretory agent", on T84 cells was also studied. We confirm the reported important increase in I SC induced by DCEBIO which was associated here with a modest secretory deltaJ W-transp. The present results were compared with those reported using the same experimental approach applied to established cell lines originating from intestinal and renal epithelial cells (Caco-2, LLC-PK1 and RCCD-1). No clear association between P HYDR and R T could be demonstrated and high P HYDR values were observed in an electrically tight epithelium, supporting the view that a "water leaky" barrier is not necessarily an "electrically leaky" one. Furthermore, the modest secretory deltaJ W-transp was not consistent with previous results obtained with RCCD-1 cells stimulated with vasopressin (absorptive fluxes) or with T84 cells secreting water under the action of Escherichia coli heat stable enterotoxin. We conclude that, while the presence of aquaporins is necessary to dissipate an external osmotic gradient, coupling between water and ion transport cannot be explained by a simple and common underlying mechanism.

Power Electronic Converters in Low-Voltage Direct Current Distribution – Analysis and Implementation

Over the recent years, smart grids have received great public attention. Many proposed functionalities rely on power electronics, which play a key role in the smart grid, together with the communication network. However, “smartness” is not the driver that alone motivates the research towards distribution networks based on power electronics; the network vulnerability to natural hazards has resulted in tightening requirements for the supply security, set both by electricity end-users and authorities. Because of the favorable price development and advancements in the field, direct current (DC) distribution has become an attractive alternative for distribution networks. In this doctoral dissertation, power electronic converters for a low-voltage DC (LVDC) distribution system are investigated. These include the rectifier located at the beginning of the LVDC network and the customer-end inverter (CEI) on the customer premises. Rectifier topologies are introduced, and according to the LVDC system requirements, topologies are chosen for the analysis. Similarly, suitable CEI topologies are addressed and selected for study. Application of power electronics into electricity distribution poses some new challenges. Because the electricity end-user is supplied with the CEI, it is responsible for the end-user voltage quality, but it also has to be able to supply adequate current in all operating conditions, including a short-circuit, to ensure the electrical safety. Supplying short-circuit current with power electronics requires additional measures, and therefore, the short-circuit behavior is described and methods to overcome the high-current supply to the fault are proposed. Power electronic converters also produce common-mode (CM) and radio-frequency (RF) electromagnetic interferences (EMI), which are not present in AC distribution. Hence, their magnitudes are investigated. To enable comprehensive research on the LVDC distribution field, a research site was built into a public low-voltage distribution network. The implementation was a joint task by the LVDC research team of Lappeenranta University of Technology and a power company Suur-Savon S¨ahk¨o Oy. Now, the measurements could be conducted in an actual environment. This is important especially for the EMI studies. The main results of the work concern the short-circuit operation of the CEI and the EMI issues. The applicability of the power electronic converters to electricity distribution is demonstrated, and suggestions for future research are proposed.

Relay protection in active distribution networks

Increasingly growing share of distributed generation in the whole electrical power system’s generating system is currently a worldwide tendency, driven by several factors, encircling mainly difficulties in refinement of megalopolises’ distribution networks and its maintenance; widening environmental concerns adding to both energy efficiency approaches and installation of renewable sources based generation, inherently distributed; increased power quality and reliability needs; progress in IT field, making implementable harmonization of needs and interests of different-energy-type generators and consumers. At this stage, the volume, formed by system-interconnected distributed generation facilities, have reached the level of causing broad impact toward system operation under emergency and post-emergency conditions in several EU countries, thus previously implementable approach of their preliminary tripping in case of a fault, preventing generating equipment damage and disoperation of relay protection and automation, is not applicable any more. Adding to the preceding, withstand capability and transient electromechanical stability of generating technologies, interconnecting in proximity of load nodes, enhanced significantly since the moment Low Voltage Ride-Through regulations, followed by techniques, were introduced in Grid Codes. Both aspects leads to relay protection and auto-reclosing operation in presence of distributed generation generally connected after grid planning and construction phases. This paper proposes solutions to the emerging need to ensure correct operation of the equipment in question with least possible grid refinements, distinctively for every type of distributed generation technology achieved its technical maturity to date and network’s protection. New generating technologies are equivalented from the perspective of representation in calculation of initial steady-state short-circuit current used to dimension current-sensing relay protection, and widely adopted short-circuit calculation practices, as IEC 60909 and VDE 0102. The phenomenon of unintentional islanding, influencing auto-reclosing, is addressed, and protection schemes used to eliminate an sustained island are listed and characterized by reliability and implementation related factors, whereas also forming a crucial aspect of realization of the proposed protection operation relieving measures.

Modelling of faults in low-voltage cables

Power line modelling has become an interesting research area in recent years as a result of advances in the power line distribution network system. Extensive knowledge about the power line cable characteristics can be implemented in a software algorithm in a modern broadband power-line communication modem. In this study, a novel approach for modelling power line cables (AMCMK) based on the broadband impedance spectroscopy (BIS) and transmission line matrix (TLM) techniques is recommended in characterizing a healthy cable and the various faults associated with low-voltage cables for both open and short circuit situation. Models for different cable conditions are developed and tuned, which include six models for both healthy and faulty cables situations. The models are on the basis of impedance response analysis of the cable. The resulting spectra from the simulations are also cross-correlated to determine the degree of similarities between the healthy cable spectra and their respective faulty spectra.