<p>This study was initiated to investigate if it could be feasible to supply offshore oil installations in the North Sea with electrical power from land. A prestudy of alternative converter topologies indicated that the most promising solution would be to investigate a conventional system with reduced synchronous compensator rating.</p><p>The study starts with a summary of the state of power supply to offshore installations today, and a short review of classical HVDC transmission. It goes on to analyse how a passive network without sources influences the inverter. The transmission, with its current controlled rectifier and large inductance, is simulated as a current source. Under these circumstances the analysis shows that the network frequency has to adapt in order to keep the active and reactive power balance until the controllers are able to react. The concept of firing angle for a thyristor is limited in a system with variable frequency, the actual control parameter is the firing delay time.</p><p>Sensitivity analysis showed some astonishing consequences. The frequency rises both by an increase in the active and in the reactive load. The voltage falls by an increase in the active load, but rises by an increase in the inductive load.</p><p>Two different control principles for the system of inverter, synchronous compensator and load are defined. The first takes the reference for the firing delay time from the fundamental voltage at the point of common coupling. The second takes the reference for the firing delay time from the simulated EMF of the synchronous compensator. Of these, the second is the more stable and should be chosen as the basis for a possible control system.</p><p>Two simulation tools are applied. The first is a quasi-phasor model running on Matlab with Simulink. The other is a time domain model in KREAN. The time domain model is primarily used for the verification of the quasi-phasor model, and shows that quasi-phasors is still a valuable tool for making a quick analysis of the main features when the details of the transients are of less importance.</p><p>The study indicates that power supply by HVDC transmission from land to offshore oil installations could be technically feasible, even without the large synchronous compensators normally required. It has been shown that in a network only supplied by an inverter, variations of active and reactive loads have significant influence on both voltage and frequency. Particularly it should be noted that the frequency shows a positive sensitivity to increases in load. This could make the system intrinsically unstable in the case of a frequency dependent load such as motors.</p><p>It was not a part of the study to optimize controllers, but even with simple controllers it was possible to keep the frequency within limits given by norms and regulations, but the voltages were dynamically outside the limits, though not very far. These voltage overswings take place in the first few instances after a disturbance, so it takes unrealistically fast controllers to handle them. They are partly due to the model, where the land based rectifier and the DC reactors are simulated by a constant current source, but partly they have to be handled by overdimensioning of the system.</p><p>The simulations indicate that it should be technically possible to supply an oil platform with electrical power from land by means of HVDC transmission with small synchronous compensators. Whether this is financially feasible has not been investigated. Neither has it been considered whether the necessary equipment can actually be installed on an oil platform.</p><p>Recently both ABB and Siemens have presented solutions for HVDC transmission in the lower and medium power range based on voltage source converters based on IGBTs. Fully controllable voltage source HVDC converters have properties that may be better suited than conventional line commutated current source thyristor inverters, to supply weak or passive networks, such as offshore oil installations, with electrical power. But they also have some disadvantages, and a complete technical and financial comparison must be performed in order to decide about any potential project.</p>

This study was initiated to investigate if it could be feasible to supply offshore oil installations in the North Sea with electrical power from land. A prestudy of alternative converter topologies indicated that the most promising solution would be to investigate a conventional system with reduced synchronous compensator rating. The study starts with a summary of the state of power supply to offshore installations today, and a short review of classical HVDC transmission. It goes on to analyse how a passive network without sources influences the inverter. The transmission, with its current controlled rectifier and large inductance, is simulated as a current source. Under these circumstances the analysis shows that the network frequency has to adapt in order to keep the active and reactive power balance until the controllers are able to react. The concept of firing angle for a thyristor is limited in a system with variable frequency, the actual control parameter is the firing delay time. Sensitivity analysis showed some astonishing consequences. The frequency rises both by an increase in the active and in the reactive load. The voltage falls by an increase in the active load, but rises by an increase in the inductive load. Two different control principles for the system of inverter, synchronous compensator and load are defined. The first takes the reference for the firing delay time from the fundamental voltage at the point of common coupling. The second takes the reference for the firing delay time from the simulated EMF of the synchronous compensator. Of these, the second is the more stable and should be chosen as the basis for a possible control system. Two simulation tools are applied. The first is a quasi-phasor model running on Matlab with Simulink. The other is a time domain model in KREAN. The time domain model is primarily used for the verification of the quasi-phasor model, and shows that quasi-phasors is still a valuable tool for making a quick analysis of the main features when the details of the transients are of less importance. The study indicates that power supply by HVDC transmission from land to offshore oil installations could be technically feasible, even without the large synchronous compensators normally required. It has been shown that in a network only supplied by an inverter, variations of active and reactive loads have significant influence on both voltage and frequency. Particularly it should be noted that the frequency shows a positive sensitivity to increases in load. This could make the system intrinsically unstable in the case of a frequency dependent load such as motors. It was not a part of the study to optimize controllers, but even with simple controllers it was possible to keep the frequency within limits given by norms and regulations, but the voltages were dynamically outside the limits, though not very far. These voltage overswings take place in the first few instances after a disturbance, so it takes unrealistically fast controllers to handle them. They are partly due to the model, where the land based rectifier and the DC reactors are simulated by a constant current source, but partly they have to be handled by overdimensioning of the system. The simulations indicate that it should be technically possible to supply an oil platform with electrical power from land by means of HVDC transmission with small synchronous compensators. Whether this is financially feasible has not been investigated. Neither has it been considered whether the necessary equipment can actually be installed on an oil platform. Recently both ABB and Siemens have presented solutions for HVDC transmission in the lower and medium power range based on voltage source converters based on IGBTs. Fully controllable voltage source HVDC converters have properties that may be better suited than conventional line commutated current source thyristor inverters, to supply weak or passive networks, such as offshore oil installations, with electrical power. But they also have some disadvantages, and a complete technical and financial comparison must be performed in order to decide about any potential project.

<p>This thesis investigates simulation of synchronous machines using a novel Magnetic Equivalent Circuit (MEC) model. The proposed model offers sufficient detail richness for design calculations, while still keeping the simulation time acceptably short.</p><p>Different modeling methods and circuit alternatives are considered. The selected approach is a combination of several previous methods added with some new features. A detailed description of the new model is given. The flux derivative is chosen as the magnetic flow variable which enables a description with standard circuit elements. The model is implemented in dq-coordinates to reduce complexity and simulation time. A new method to reflect winding harmonics is introduced.</p><p>Extensive measurements have been made to estimate the traditional dq-model parameters. These in combination with analytical calculations are used to determine the parameters for the new MEC model.</p><p>The model is implemented using the Dymola simulation program. The results are evaluated by comparison with measurements and FEM simulations. Three different operation cases are investigated; synchronous operation, asynchronous start and inverter fed operation. The agreement with measurements and FEM simulations varies, but it is believed that it can be improved by more work on the parameter determination.</p><p>The overall conclusion is that the MEC method is a useful approach for detailed simulation of synchronous machines. It enables proper modeling of magnetic saturation, and promises sufficiently detailed results to enable accurate loss calculations. However, the experience is that the complexity of the circuits should be kept at a reasonable low level. It is believed that the practical problems with model structure, parameter determination and the simulation itself will otherwise be difficult to master.</p>

<p>This thesis tries to explain the changes in the control of power electronic converters that are possible by the use of communication. Many of the renewable energy sources such as photovoltaic panels are geographically dispersed. The power rating per generator is therefore typically low. If this kind of energy source should dominate an electrical grid, the number of generators must be high. There should also be means of controlling this large number of generators simultaneously and safely. The cost of safe communication may be too high compared to the power contribution of a single generator. The Internet offers a low-cost solution, but it cannot guarantee real-time properties. Similarly to the Internet itself, it is shown how communication errors can be detected and handled in a safe manner by the end-system, in this case the generator. The generator can detect a communication timeout, and change control algorithms in order to guard itself and the connected electricity grid. When necessary, it can also disconnect and work as a local standalone power supply. In order to be able to supply all kinds of loads, the generator (in this case an inverter) is primarily voltage controlled. This results in challenges concerning current distortion. The use of feed-forward for cancellation of common grid voltage harmonics is discussed, simulated and measured. An anti-islanding algorithm for voltage controlled inverters is also developed, simulated and measured in this thesis. A DC/DC-converter for optimized connection of a photovoltaic panel is built, exploiting the photovoltaic panel properties to reduce the size and the losses significantly. Although most contributions are connected to details and parts of the system, the interactions between communication and control are emphasized.</p>

<p>After decades of power generating units increasing in size, there is currently a growing focus on distributed generation, power generation close to energy loads. Investments in large-scale units have been driven by economy of scale, but recent technological improvements on small generating plants have made it possible to exploit the benefits of local power generation to a larger extent than previously. Distributed generation can improve power system efficiency because heat can be recovered from thermal units to supply heat and thermally activated cooling, and because small-scale renewables have a promising end-user market. Further benefits of distributed generation include improved reliability, deferral of often controversial and costly grid investments and reduction of grid losses. The new appeal of small-scale power generation means that there is a need for new tools to analyze distributed generation, both from a system perspective and from the perspective of potential developers. In this thesis, the focus is on the value of power generation for end-users. The thesis identifies how an end-user can find optimal distributed generation systems and investment strategies under a variety of economic and regulatory scenarios. The final part of the thesis extends the analysis with a bottom-up model of how the economics of distributed generation for a representative set of building types can transfer to technology diffusion in a market.</p><p>Four separate research papers make up the thesis. In the first paper, Optimal Investment Strategies in Decentralized Renewable Power Generation under Uncertainty, a method for evaluation of investments in renewable power units under price uncertainty is presented. It is assumed the developer has a building with an electricity load and a renewable power resource. The case study compares a set of wind power systems with different capacity and finds that capacity depends on the electricity price and that there under uncertain prices can be a significant value in postponing investment until larger projects are profitable. In the second paper, Combined Heat and Power in Commercial Buildings: Investment and Risk Analysis, a Monte Carlo simulation program to find the value and risk characteristics of combined heat and power units is presented. Using historical price data to estimate price process parameters, it is shown that uncertain prices should not be a barrier for investment, since on-site generators can adapt to uncertain prices and reduce the total energy cost risks. In, Optimizing Distributed Generation Systems for Commercial Buildings, which uses a mixed integer linear program, distributed generation portfolios that maximize profitability are tailored to a building's energy load. Distributed generation with heat recovery and thermally activated cooling are found profitable in an office and a health care building, using current generator data and energy tariffs from California. With the fourth paper, Distributed Energy Resources Market Diffusion Model, the analysis is taken a step further to predict distributed generation market diffusion. Market penetration is assumed to depend on economic attractiveness and knowledge and trust in the technologies. A case study based on the U.S. commercial sector depicts a large market for reciprocating engines and microturbines, with the West and Northeast regions driving market diffusion. Technology research and outreach programs can speed up and change the path of capacity expansion.</p><p>The thesis presents three different models for analyzing investments in distributed generation, all of which have benefits and disadvantages. Choice of model depends on the specific application, but the different approaches can be used on the same problem to analyze it from different viewpoints. The cases in the thesis indicate that distributed generation can reduce expected energy costs while at the same time improve cost predictability. Further, the thesis identifies several important factors and potential barriers to distributed generation adoption. Analyzing distributed generation from the end-user perspective is important also for policy makers, because of the importance of estimating how the market will react to potential policy measures. The thesis shows that small-scale generating capacity has the potential to increase in the near future. Further research should increase the understanding of economic and environmental issues related to distributed generation, while policy makers should aim to construct and implement measures that make it attractive for end-users to invest in efficient local generating capacity.</p>

<p>OKG AB äger de tre kokvattenreaktorerna Oskarshamn 1, 2 och 3. Kärnkraftverket ligger i Simpevarp norr om Oskarshamn. Examensarbetet har utförts på Oskarshamn 1 inom ett projekt som kallas CEM. Oskarshamn 1 togs i drift 1972 och kan leverera en elektrisk effekt på 491 MW.</p><p>Examensarbetet behandlar underhållsaspekter som bör tas hänsyn till vid projektering och konstruktion av det nya automatiskt gasturbinsäkrade 6,3 kV ställverket i system 642. Ställverket är huvudfördelningsställverk inom Oskarshamn 1 och ska bytas ut på grund av hög ålder samt brist på reservdelar.</p><p>I syfte att uppnå hög driftsäkerhet och tillgänglighet för det nya ställverket har aspekter som förbättrar dess funktionssäkerhet, underhållsmässighet och underhållssäkerhet specificerats. Förslag på ny lastfördelning samt uppställning av ställverkets fack ges också.</p><p>Resultatet av examensarbetet är de framtagna underhållsaspekter som kan tillämpas vid projektering och konstruktion av ställverket. De viktigaste underhållsaspekterna som tagits fram är att utrustningen ska vara personsäker, det ska finnas tillräckligt med utrymme i facken för att kunna utföra underhållsarbete samt att fullständig dokumentation ska levereras samtidigt som utrustningen. Ett förslag till ny lastfördelning av ställverkets belastningar har utförts utifrån en teknisk specifikation. Förslaget på uppställning av ställverkets fack tyder på att tillräckligt utrymme finns i befintliga ställverksrum.</p> / <p>OKG AB is the owner of the three boiling water reactors Oskarshamn 1, 2 and 3. The nuclear power plant is located in Simpevarp north of Oskarshamn. The thesis has been carried out at Oskarshamn 1 within a project called CEM. Oskarshamn 1 started to produce electricity in 1972 and can today deliver an electrical power of 491 MW.</p><p>The thesis considers maintenance aspects which are to be taken into consideration before planning and construction of the new automatic gas turbine secured switchgears in system 642. The switchgears are the main distribution switchgears within Oskarshamn 1 and are to be replaced because of high age and lack of spare parts.</p><p>In purpose to achieve high availability performance and availability for the switchgears, aspects which improves the reliability, maintainability and maintenance supportability has been specified. Suggestion of new distribution of the loads between the busbars and arrangement of the cubicles has also been carried out and specified.</p><p>The results of the thesis are the specified maintenance aspects which can be used when planning and constructing the switchgears. The most important maintenance aspects are that the equipment has high personnel safety, that there is enough space in the cubicles to perform maintenance and that a complete documentation is delivered together with the equipment. Suggestion of new load distribution between the busbars has been carried out with the help of a technical specification. The suggestion of new arrangement for the switchgears implies that there is enough space in the existing electrical room for the switchgears.</p>

<p>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.</p>

After decades of power generating units increasing in size, there is currently a growing focus on distributed generation, power generation close to energy loads. Investments in large-scale units have been driven by economy of scale, but recent technological improvements on small generating plants have made it possible to exploit the benefits of local power generation to a larger extent than previously. Distributed generation can improve power system efficiency because heat can be recovered from thermal units to supply heat and thermally activated cooling, and because small-scale renewables have a promising end-user market. Further benefits of distributed generation include improved reliability, deferral of often controversial and costly grid investments and reduction of grid losses. The new appeal of small-scale power generation means that there is a need for new tools to analyze distributed generation, both from a system perspective and from the perspective of potential developers. In this thesis, the focus is on the value of power generation for end-users. The thesis identifies how an end-user can find optimal distributed generation systems and investment strategies under a variety of economic and regulatory scenarios. The final part of the thesis extends the analysis with a bottom-up model of how the economics of distributed generation for a representative set of building types can transfer to technology diffusion in a market. Four separate research papers make up the thesis. In the first paper, Optimal Investment Strategies in Decentralized Renewable Power Generation under Uncertainty, a method for evaluation of investments in renewable power units under price uncertainty is presented. It is assumed the developer has a building with an electricity load and a renewable power resource. The case study compares a set of wind power systems with different capacity and finds that capacity depends on the electricity price and that there under uncertain prices can be a significant value in postponing investment until larger projects are profitable. In the second paper, Combined Heat and Power in Commercial Buildings: Investment and Risk Analysis, a Monte Carlo simulation program to find the value and risk characteristics of combined heat and power units is presented. Using historical price data to estimate price process parameters, it is shown that uncertain prices should not be a barrier for investment, since on-site generators can adapt to uncertain prices and reduce the total energy cost risks. In, Optimizing Distributed Generation Systems for Commercial Buildings, which uses a mixed integer linear program, distributed generation portfolios that maximize profitability are tailored to a building's energy load. Distributed generation with heat recovery and thermally activated cooling are found profitable in an office and a health care building, using current generator data and energy tariffs from California. With the fourth paper, Distributed Energy Resources Market Diffusion Model, the analysis is taken a step further to predict distributed generation market diffusion. Market penetration is assumed to depend on economic attractiveness and knowledge and trust in the technologies. A case study based on the U.S. commercial sector depicts a large market for reciprocating engines and microturbines, with the West and Northeast regions driving market diffusion. Technology research and outreach programs can speed up and change the path of capacity expansion. The thesis presents three different models for analyzing investments in distributed generation, all of which have benefits and disadvantages. Choice of model depends on the specific application, but the different approaches can be used on the same problem to analyze it from different viewpoints. The cases in the thesis indicate that distributed generation can reduce expected energy costs while at the same time improve cost predictability. Further, the thesis identifies several important factors and potential barriers to distributed generation adoption. Analyzing distributed generation from the end-user perspective is important also for policy makers, because of the importance of estimating how the market will react to potential policy measures. The thesis shows that small-scale generating capacity has the potential to increase in the near future. Further research should increase the understanding of economic and environmental issues related to distributed generation, while policy makers should aim to construct and implement measures that make it attractive for end-users to invest in efficient local generating capacity.

This thesis tries to explain the changes in the control of power electronic converters that are possible by the use of communication. Many of the renewable energy sources such as photovoltaic panels are geographically dispersed. The power rating per generator is therefore typically low. If this kind of energy source should dominate an electrical grid, the number of generators must be high. There should also be means of controlling this large number of generators simultaneously and safely. The cost of safe communication may be too high compared to the power contribution of a single generator. The Internet offers a low-cost solution, but it cannot guarantee real-time properties. Similarly to the Internet itself, it is shown how communication errors can be detected and handled in a safe manner by the end-system, in this case the generator. The generator can detect a communication timeout, and change control algorithms in order to guard itself and the connected electricity grid. When necessary, it can also disconnect and work as a local standalone power supply. In order to be able to supply all kinds of loads, the generator (in this case an inverter) is primarily voltage controlled. This results in challenges concerning current distortion. The use of feed-forward for cancellation of common grid voltage harmonics is discussed, simulated and measured. An anti-islanding algorithm for voltage controlled inverters is also developed, simulated and measured in this thesis. A DC/DC-converter for optimized connection of a photovoltaic panel is built, exploiting the photovoltaic panel properties to reduce the size and the losses significantly. Although most contributions are connected to details and parts of the system, the interactions between communication and control are emphasized.

In the present climate of deregulation and privatisation, theutilities are often separated into generation, transmission anddistribution companies so as to help promote economic efficiencyand encourage competition. Also, environmental concerns,right-of-way and cost problems have delayed the construction ofboth generation facilities and new transmission lines while thedemand for electric power has continued to grow, which must bemet by increased loading of available lines. A consequence isthat power system damping is often reduced which leads to a poordamping of electromechanical power oscillations and/or impairmentof transient stability. The aim of this thesis is to examine theability of Controllable Series Devices (CSDs), such as Unified Power Flow Controller (UPFC)   Controllable Series Capacitor (CSC)   Quadrature Boosting Transformer (QBT)   for improving transient stability and damping ofelectromechanical oscillations in a power system. For these devices, a general model is used in power systemanalysis. This model is referred to as injection model which isvalid for load flow and angle stability analysis. The model isalso helpful for understanding the impact of the CSDs on powersystem stability. A control strategy for damping of electromechanical poweroscillations is also derived based on Lyapunov theory. Lyapunovtheory deals with dynamical systems without input. For thisreason, it has traditionally been applied only to closed-loopcontrol systems, that is, systems for which the input has beeneliminated through the substitution of a predetermined feedbackcontrol. However, in this thesis, Lyapunov function candidatesare used in feedback design itself by making the Lyapunovderivative negative when choosing the control. This controlstrategy is called Control Lyapunov Function (CLF) for systemswith control input. / QC 20100609