In this bachelor thesis, cable fault locators are studied for use on the overhead electrode lines in the HVDC (High Voltage Direct Current) Light project Caprivi Link. The cable fault locators studied operates with the principle of travelling waves, where a pulse is sent in the tested conductor. The time difference is measured from the injection moment to the reflection is received. If the propagation speed of the pulse is known the distance to the fault can be calculated. This type of unit is typically referred to as a TDR (Time Domain Reflectometer). The study is performed as a computer simulation where a simplified model of a TDR unit is created and applied to an electrode line model by using PSCAD/EMTDC. Staged faults of open circuit and ground fault types are placed at three distances on the electrode line model, different parameters of the TDR units such as pulse width and pulse amplitude along with its connection to the electrode line are then studied and evaluated. The results of the simulations show that it is possible to detect faults of both open circuit and ground fault types with a suitable TDR unit. Ground faults with high resistance occurring at long distances can be hard to detect due to low reflection amplitudes from the injections. This problem can somewhat be resolved with a function that lets the user compare an old trace of a “healthy” line with the new trace. The study shows that most of the faults can be detected and a distance to the fault can be calculated within an accuracy of ± 250 m. The pulse width of the TDR needs to be at least 10 μs, preferable 20 μs to deliver high enough energy to the fault to create a detectable reflection. The pulse amplitude seams to be of less significance in this simulation, although higher pulse amplitude is likely to be more suitable in a real measurement due to the higher energy delivered to the fault. The Hipotronics TDR 1150 is a unit that fulfil these requirements and should therefore be able to work as a line fault locator on the electrode line.

A relatively new application for the laser is in fluorescence microscopes. The fluo- rescence microscope needs a high power light source input. Using a laser source improves the precision of the microscope. A pulsed laser source enhances the performance of the fluorescence microscope and a laser diode can be overdriven without being damaged. The thesis investigates which properties of the laser pulses are needed regarding pulse width, pulse period and waveform. The thesis also investigates which properties are desired for the electrical pulses driving the laser, and how they can be generated using electrical components. The desired laser pulse should have a pulse width of 100 ps and a pulse period of 50 ns. The laser pulse should also have a well-defined wavelength, stable output power and it should be able to quickly turn on and off. To achieve this laser pulse, the desired input to the laser diode should have an input voltage of 5 V, an input current of 250 mA, a pulse width of 100 ps and a pulse period of 50 ns. For generating this pulse the chosen pulse generator, an SRD, should have low junction capacitance, low package capacitance and low package inductance. The chosen amplifier, a MESFET, desires low drain current and should have high transconductance and a large negative threshold voltage.

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New European energy policies have set a goal of a high share of renewable energy in electricity markets. In the presence of high levels of renewable generation, and especially wind, there is more uncertainty in the supply. It is natural, that volatility in energy production induces the volatility in energy prices. This can create incentives for the generators to exercise market power by traditional means: withholding the output by conventional generators, bidding not the true marginal costs, or using locational market power. In addition, a new type of market power has been recently observed: exercise of market power on ramp rate. This dissertation focuses on modeling the exercise of market power in power systems with high penetration of wind power. The models consider a single, or multiple profit-maximizing generators. Flexibility is identified as one of the major issues in wind-integrated power systems. Therefore, part of the research studies the behavior of strategic hydropower producers as main providers of flexibility in systems, where hydropower is available.Developed models are formulated as mathematical and equilibrium problems with equilibrium constraints (MPECs and EPECs). The models are recast as mixed-integer linear programs (MILPs) using discretization. Resulting MILPs can be solved directly by commercially-available MILP solvers, or by applying decomposition. Proposed Modified Benders Decomposition Algorithm (MBDA) significantly improves the computational efficiency. / <p>QC 20170516</p>

The objective of this Thesis is to investigate the phenomenon of voltage unbalance on electrical wind power systems. A large part of this work is the literature review of all relative work that has been done so far. This serves first as a guideline to define and measure voltage unbalance and second as a tool to spot open research questions that can inspire future work. A case study is then used to investigate the voltage unbalance at a wind farm in Näsudden, Gotland. Using real-time measurements and a simulation of the power system in MATLAB/Simulink, an evaluation of the propagation of the voltage unbalance from the distribution to the turbine level is carried out. The effect that different transformer connection types have on the propagation is studied through simulations. Many assumptions and simplifications had to be made due to several limiting factors during this work, mainly related to time and data restrictions. The main result shows that when Delta – Wye Grounded and Wye – Wye Grounded transformers are used, the unbalance is halved when it passes to the turbine side. On the other hand, when Wye Grounded – Wye Grounded configuration was used, the unbalance was unaffected. The results also include a comparison of the use of different indices to quantify a voltage unbalance.

Power system transmission is undergoing rapid changes by the advent of renewable resources of energy, distributed generation, market integration, etc. Transmission planning is, nowadays, about building more inter-connections between adjacent regions or connecting off-shore wind farms to the grid or augmenting the network to support new path flows of energy and is still almost entirely the responsibility of regulated transmission system operator (TSO). Moreover, a well-developed transmission planning includes anticipating the generation investment decisions made by profit-maximizing generation companies (Gencos). Ensuring sustainable development of the power system necessitates coordination between TSO transmission investment with Gencos generation investments. Moreover, coordination between inter-connected TSOs in planning the network is also required in order to hunter the economic benefits of a robust and efficiently planned multi-area power system. Driven by the need for more coordination of the long-term planning of the inter-connected power systems, this thesis aims to develop models to be used in analysis of the multi-TSO multi-Genco transmission and generation planning and suggest mechanisms and coordination approaches for the better functioning of the power system. This includes mathematical models for transmission planning in the context of multiple TSOs and generation-transmission investment planning based on the game theory concepts in applied mathematics and evaluating mechanisms and approaches. / <p>QC 20161110</p>

In Cu(In,Ga)Se2 (CIGS) solar cells the CIGS layer serves as the light absorber, growing naturally p-type. Together with an n-type buffer layer they form a p-n heterojunction. Typically, CdS is used as a buffer, although other, less toxic materials are investigated as alternatives. The intrinsic p-type doping of CIGS layers is the result of complex defect physics. Defect formation energies in CIGS are very low or even negative, which results in extremely high defect concentrations. This leads to many unusual electrical phenomena that can be observed in CIGS devices. This thesis mostly focuses on three of these phenomena: light-soaking, light-on-bias, and light-enhanced reverse breakdown. Light-soaking is a treatment that involves illuminating the investigated device for an extended period of time. In most CIGS solar cells it results in an improvement of open-circuit voltage, fill factor, and efficiency that can persist for hours, if not days. The interplay between light-soaking and the remaining two phenomena was studied. It was found that light-soaking has a strong effect on light-on-bias behavior, while the results for light-enhanced breakdown were inconclusive, suggesting little to no impact. Light-on-bias is a treatment which combines simultaneous illumination and application of reverse bias to the studied sample. Illuminating CdS-based samples with red light while applying a reverse bias results in a significant increase in capacitance due to filling of traps. In many cases, this is accompanied by a decrease in device performance under red illumination. Complete recovery is possible by illuminating the treated sample with blue light, which causes hole injection from the CdS buffer. In samples with alternative buffer layers, there is little distinction between red and blue illumination, and the increase in capacitance is milder. At the same time, there is little effect on device performance. Reverse breakdown can occur when a sufficiently large reverse bias is applied to a p-n junction, causing a large reverse current to flow through the device. In CIGS solar cells, the voltage at which breakdown occurs in darkness decreases in the presence of blue illumination. A model explaining the breakdown in darkness was proposed as a part of this thesis. The model assumes that all voltage drops on the buffer layer in darkness and on the CIGS layer under blue illumination. The high electric field in the buffer facilitates Poole-Frenkel conduction and Fowler-Nordheim tunneling between the absorber and the buffer.

Företag med en produktportfölj inriktad mot maskinsäkerhet har ett stort behov av att kunna visa upp produkterna i en integrerad helhetslösning. Men det ställer då också krav på att kunna vägleda och utbilda kunderna inom området maskinsäkerhet. Målet med denna uppsats har varit att ge-nomföra en riskanalys och ta fram två säkerhetslösningar på ett något av-skalat valsverk. Resultatet ska sedan användas i ett säljverktyg i form av en portabel DEMO för framtida mässor och utbildningar. Under arbetets gång så har ett flertal studiebesök och intervjuer genomförts med personer som har en lång erfarenhet av maskinsäkerhet och valsverk. Som stöd under ris-kanalysen så har bland annat den harmoniska standarden SS EN ISO 13849-1:2016 används. Först bestämdes maskinens omfattning följt av en riskbe-dömning där tänkta riskkällor identifierats och där sedan en lämplig åtgärd vidtagits för att vid behov reducera risken. En validering har slutligen ge-nomförts som ett sista steg i analysen för att säkerställa att med aktuellt framtagna skyddsfunktioner nå upp till den erforderliga prestandanivå som krävs. Bearbetning av material har uteslutande genomförts via Micro-soft Excel. Beräkningar och validering av samtliga skyddsfunktioner har genomförts analogt enligt standarden EN ISO 13849-1&amp;2. Det har under ar-betets gång visat sig att det finns utrymme för tolkning och tveksamheter rörande arbetsmetod enligt ISO 13849-1 och maskindirektivet 2006/42/EC. Resultatet i undersökningen har påvisat att den först framtagna säkerhets-lösningen är den mest ultimata gällande kostnad. Medan den andra säker-hetslösningen från undersökningen är den mest optimala med avseende på flexibilitet och säkerhet. När det gäller olika tillvägagångssätt vid beräkning av skyddsfunktioner så är ett förgrenat synsätt fördelaktigt vid säkerhets-lösningar som kräver något högre prestandanivå. Det förgrenade synsättet medför dock i regel mer arbetet eftersom att antalet skyddsfunktioner beror på antalet maskiner för respektive ingångsblock. Det seriella tillvägagångs-sättet medför i regel mindre arbete vid beräkningar eftersom att antalet skyddsfunktioner då är lika med antalet ingångsblock för skyddsfunkt-ionen. Undersökningen har dessutom påvisat en tydlig korrelation mellan antalet maskiner och sannolikheten för farligt fel per timme. Det innebär att det seriella tillvägagångssättet kan leda till att aktuellt krav rörande pre-standanivå inte går att uppnå. / Companies with a portfolio that are focused at machine safety have a great need to display their products in an integrated comprehensive solution. But it’s also important for the companies to be able to guide and support cus-tomers in the field of machine safety. The aim of this report was to conduct a risk assignment and to develop two safety solutions for a cold rolling mill. The result of this report will then be used in a sales tool as a portable demon-stration platform for future fairs and customer education. During the inves-tigation, a number of study visits and interviews have been conducted with people who have a long experience of machine safety and cold rolling mills. As a guidance of the risk assignment, the harmonic standard SS EN ISO 13849-1: 2016 has been used. First, the extent of the machine was deter-mined, followed by a risk estimation where imaginary hazards were iden-tified. In case of an identified hazard an appropriate action was taken to reduce the risk. Finally, a validation was carried out as a final step in the analysis to ensure that the currently developed safety functions has reached the required performance level from the risk estimation. Processing of ma-terials has been performed exclusively through Microsoft Excel. Calcula-tions and validation of all protection features have been performed accord-ing to ISO 13849-1. During the study, it has been found that there is scope for interpretation and doubts regarding to the working methods in ISO 13849-1. The investigation was been shown that the first developed safety solution is the best regarding to the total cost. The second developed solu-tion was most optimal in terms of flexibility and security. The work has also shown that different approaches due to the calculations of the safety func-tions are important for the result. The branched method is advantageous for safety solutions that requires higher performance level but the method also in general entails additional work do to the calculations in comparison with the serial method. On the other hand, the survey showed a clear correlation between the numbers of integrated machines and the probability of danger-ous failure per hour do to the serial method. This means that the serial method can lead to the fact that the current Performance level can’t be achieved.

The awareness of the problems with fossil energy sources have increased the past decades. To decrease the effects of the fossil fuels on the climate and the environment, the use of intermittent energy sources such as solar- and wind power are increasing. Intermittent generation creates instability in the power grid, which cause fluctuations in the voltage and the frequency of the power grid. To be able to handle these fluctuations, regulating capacity such as for example pumped storage or batteries are needed. This thesis has investigated how the placement and the power capacity of a battery energy storage system affects the possibility for frequency and voltage regulation in a weak distribution grid. The investigation was made in MATLAB Simulink by creating a weak radial distribution grid with a high penetration of solar power. The distribution grid had variable loads with different power consumption at each bus, creating instability in the distribution grid. The optimal placement of a battery energy storage system is firstly at the largest load and secondly as far away from the other power generation units as possible. A battery storage with a power capacity that can handle all consumption is optimal. It is possible to have a smaller power capacity if the grid is stable enough to withstand the appearing fluctuation of frequency or voltage. The frequency variations are more dependent on the power capacity and the voltage variations are more dependent on the placement of the battery energy storage system. ISSN:

Biosensors are devices that detect biological elements and then transmit a readable signal. Biosensors can automatize diagnostics that would otherwise have to be performed by a physician or perhaps not be possible to perform at all. Current biosensors are however either limited to particular diseases or prohibitively expensive. In order to further the field, sensors capable of many parallel measurements at a lower cost need to be developed. Field effect transistor (FET) based sensors are possible candidates for delivering this, mainly by allowing miniaturization. Smaller sensors could be cheaper, and enable parallel measurements. Graphene is an interesting material to use as the channel of FET-sensors. The low electrochemical reactivity of its plane makes it possible to have graphene in direct contact with the sample liquid, which enhances the signal from impedance changes. Graphene-FET based impedance sensors should be able to sense almost all possible analytes and allow for scaling without losing sensitivity. In this work the steps needed to make graphene based biosensors are presented. An improved graphene transfer is described which by using low pressure to dry the graphene removes most contamination. A method to measure the contamination of graphene by surface enhanced Raman scattering is presented. Methods to produce double gated and electrolyte gated graphene transistors on a large scale in an entirely photolithographic process are detailed. The deposition of 1-pyrenebutyric acid (PBA) on graphene is studied. It is shown that at high surface concentrations the PBA stands up on graphene and forms a dense self-assembled monolayer. A new process of using Raman spectroscopy data to quantify adsorbents was developed in order to quantify the molecule adsorption. Biosensing has been performed in two different ways. Graphene FETs have been used to read the signal generated by a streaming potential setup. Using FETs in this context enables a more sensitive readout than what would be possible without them. Graphene FETs have been used to directly sense antibodies in high ionic strength. This sensing was done by measuring the impedance of the interface between the FET and the electrolyte.