<p>This thesis presents the laboratory test data on Bisphenol A epoxy insulation.This thesis work deals with electrical, mechanical and thermal analysis of Bisphenol A epoxy resin. The main aim of this thesis work was to examine if dry and wet aging changes the glass transition temperature (Tg) of the epoxies and measure the impact on the complex permittivity under different ageing conditions namely dry and wet. During ageing the samples (epoxy discs and dog bones) were kept in water at 20°C, 45°C and 80°C both in dry and wet conditions for a period of one month. After the samples were removed from ageing they were conditioned in a vacuum oven for one week. The effect of temperature and relative humidity on unaged epoxy i.e. dry characterization was determined by keeping the samples in climate chamber with 15%RH (Relative Humidity) and temperatures 20°C, 45°C and 80°C. The wet characterization was carried out with 90%RH and temperatures 20°C, 45°C and 80°C. The surface of these samples was painted with silver paint (electrodes). Two circular discs were used for dielectric response measurement and 2 rectangular pieces for water sorption measurement. The dielectric response was measured when equilibrium/saturation condition was achieved. The dielectric response was measured in the frequency range from 0.01 Hz to 1000 Hz at 200 volts (peak). The wet characterization showed increases with aging temperature. The dielectric loss was also increasing with the temperature. It can be deduced that the water uptake by the epoxy increases with increase in humidity and temperature. The dry characterization showed and has steady growth with aging temperature. Therefore it can be deduced that characterization done in dry condition didn’t significantly affect the complex permittivity as compared with wet characterization. The glass transition temperature (Tg) of the samples were found using DSC (Differential Scanning Calorimetry) with a heating rate 20°C/min. The Tg was measured in the samples in dry condition before the water absorption process, then in samples after the water absorption process with moisture in the sample, and then in sample after the desorption. The effect of water on the Tg of the epoxy polymer was studied. Tg was increasing with aging temperature, for both dry as well as wet samples. The increase in the value can be mainly attributed to post curing process of the epoxy. The mechanical strength of the epoxy was studied by applying a tensile force to the dog bone shaped samples till breakdown and the stress versus strain curve was detected. This test was also performed on the dry aged sample before water absorption, then in sample which was kept under water at 20°C ,45°C and 80°C for absorption, and in sample which has undergone absorption and desorption at 20°C ,45°C and 80°C. The difference between the stress-strain curves was documented and discussed. The ageing temperature plays a significant role in reducing the value of stress and percentage strain at max. For dry aged epoxy, stress reduces around 14% from 200C to 800C. However for wet aged epoxy samples tensile strength reduces around 25%. For dry aged samples % strain reduces around 0,3 %. and for wet aged samples it reduces around 0,5%.</p>

<p>This master thesis treats the research of a novel “generator with converter” design called “Doubly Fed Permanent Magnet Synchronous Machine”, DF-PMSM, patented by SmartMotor. The thesis includes an introduction to the machine, a state-of-the-art survey, a hydro power case, simulations and a laboratory experiment. The DF-PMSM concept adds an important feature to fixed speed PMSM systems; the reactive power can be regulated. Compared to a direct coupled PMSM the DF-PMSM concept can add voltage control (by controlling the reactive power) in addition to active power control. The concept is based on a 6-phase Permanent Magnet Synchronous Machine where the windings are grouped into two sets of 3-phase, both situated in the stator. These winding sets are named “control” and “power” winding, named after their purpose in the design. The “control winding” is routed through a converter with active-front-end rectifier. It will be used to control the reactive power and the active power from the control winding. The “power winding” will carry most of the generated power, directly coupled and in sync with the voltages of the connected grid. The state-of-the-art survey includes constant speed and variable speed generators utilized in hydro power generation today. It also includes some general info about doubly fed and multiphase machines. The grid regulations for Norway are also investigated to give a pointer to what requirements that the DF-PMSM needs to fulfill to be connected to the grid. The machine simulations are done in LTspice where machine simulation models are developed for this purpose. Simulation of machine startup and changes is load is done. The simulation models are developed as hierarchical sub blocks that can be re used in later simulation cases. The laboratory is done with two machines in back-to-back configuration with industry standard converters. The DF-PMSM is made from a 3-phase permanent magnet machine that is rewired to a 6-phase configuration. The laboratory exercise includes start up, synchronization of the power winding to the grid, machine loading and reactive power compensation by the active front end converter. The DF-PMSM is confirmed working and design considerations are given based experience gained from working with this design. All of this information is included in this report and the further work needed before this machine is constructed and sold is sketched in the conclusion.</p>

<p>Four samples of galvanized steel armour for sub sea power cables are tested with an electric steel tester. The samples exhibit different remanence magnetization and permeability. The effects of permeability on loss in sub sea cables is found to be insignificant. Slight increase of conductor inductance due to increase in permeability of armour wires is observed. Mutual cancellation of inductance between circuits that are twisted opposite to each other, or with respect to one circuit, is confirmed with laboratory tests and measurements on full scale sub sea power cables. The parameters of one cable is calculated using IEC’s analytical approach and found to be inaccurate for conductor resistance. The Calculations places 22% of total cable loss in the armour. Measurements on two sub sea cables and analysis using finite element method contradict the calculated armour loss. Parameters for two sub sea power cables are calculated based on measurements performed on the actual cables. The calculated values are compared with values computed using finite element analysis. Derived physics from laboratory experiments and measurements on the cables is applied in finite element analysis and found to be accurate compared with calculated values from measurements and computed values using Flux 2.5D.</p>

<p>This degree project concludes the Innovation and Design Engineering programme at Karlstad University. The project was carried out by David Brocker, Erik Hallberg and Andreas Hertzman during the spring of 2006 and corresponded to 15 weeks of work per student. Assigner was Martin Larsson at Arexor and instructor at Karlstad University was Monica Jakobsson.</p><p>Arexor has a patent to a construction of an electrical skirting board with moveable wall sockets, called Electrical Track System. The lowest parts of the interior walls along the floor are today almost always covered by a conventional skirting board. Arexors patented product replaces that with the possibility to move and increase the number of wall sockets by choice along an electrical skirting board. Conventional wall sockets are limited due to fixed positions and are not transferable. It causes a problem when the number of fixed wall sockets controls the possibilities and not the users demand.</p><p>The assignment commissioned by Arexor to the students was to improve and develop the Electrical Track System because the patent did not fulfil the requirements for CE certification. The project results were to be used by Arexor as the basic data when the product was tested by ETL SEMKO.</p><p>The objective of the project was to present directions for production to a functioning prototype of the Electrical Track System, within the estimated time period. The prototype was to be shown at the exhibition for degree projects at Karlstad University in May 2006. The objective also included to create a product brochure and a display case.</p><p>The development method were divided into five phases: preparation phase, research phase, idea generating phase, conception development phase and concretisation phase. They were carried out linear up to the conception development phase. Then iteration between the research phase, idea generating phase, conception development phase was repeated until satisfied result was achieved.</p><p>The result included a number of functioning prototypes, a display case, a product brochure, CAD drawings, renderings and this academic report. The prototypes were manufactured by Modellteknik in Eskilstuna, Sweden.</p><p>Parts of the result cannot be presented due to that the solutions was not, at the time, protected by the patent. Arexor announced in the end of the project that they would apply for a new patent that included our solutions. Because of that these solutions could not be shown in public. Some parts in the report therefore refer to secrecy.</p> / <p>Detta examensarbete var avslutningen på Innovations- och designingenjörsprogrammet vid Karlstads universitet på fakulteten för teknik- och naturvetenskap. Arbetet genomfördes av David Brocker, Erik Hallberg och Andreas Hertzman under våren 2006 på uppdrag av Arexor och omfattade 15 högskolepoäng per student. Uppdragsgivare på Arexor var Martin Larsson och handledare var Monica Jakobsson från Karlstads universitet.</p><p>Arexor har patenterat en konstruktion av en elektrisk golvlist med flyttbara vägguttag, kallat Electrical Track System. Längs med golvet utmed väggarna sitter i fastigheter i dag nästan alltid en golvlist. Arexors patenterade produkt ersätter golvlisten och ger möjlighet att bland annat flytta, montera och öka antalet vägguttag längs med listen efter eget behov. Traditionella uttag begränsas av att de har fasta positioner och inte kan omplaceras. Det innebär problem då antalet fasta uttag styr möjligheterna och inte behovet.</p><p>Uppdraget som Arexor gav projektgruppen var att vidareutveckla Electrical Track System, då patentet inte uppfyllde kraven för CE-certifiering. Resultatet av arbetet skulle sedan användas av Arexor som underlag vid test hos ETL SEMKO.</p><p>Målet var att ta fram tillverkningsunderlag för en slutgiltig, fungerande prototyp av ETS inom tidsramen för projektet. Den skulle sedan visas på examensutställningen vid Karlstads universitet den 30 maj 2006. Delmål var även att ta fram en produktbroschyr och en utställningsmonter.</p><p>Arbetet delades in i stegen arbetsplan, förstudie, idégenerering, konceptutveckling och konkretisering. De genomfördes linjärt upp till konceptutvecklingen, sedan skedde en iteration mellan stegen förstudie, idégenerering och konceptutveckling. Det betyder att processen upprepades tills det att önskat resultat uppnåddes.</p><p>Resultatet blev en mängd olika fungerande prototyper, en utställningsmonter, en produktbroschyr, CAD-ritningar, renderingar och denna akademiska rapport. Prototyperna tillverkades i samarbete med Modellteknik i Eskilstuna.</p><p>Delar av resultatet redovisas inte på grund av att lösningarna inte vid tidpunkten skyddades av rådande patent. Arexor meddelande i slutet av projektet att företaget skulle ansöka om ett nytt patent där dessa lösningar inkluderades. Det medförde att lösningarna inte fick offentliggöras innan patentansökan hade lämnats in. Därför hänvisas till sekretess i vissa delar av rapporten.</p>

In this master thesis the theory and practical use of modal analysis is explained, giving an introduction to the possibilities of modal analysis. The master thesis starts with a look at wind power and the design of a modern wind turbine. Two models, one for constant wind speed wind turbines and one for variable speed wind turbines, are presented. An example shows how modal analysis can be utilized to evaluate a network's dynamic stability. Simulations are performed on a two-area network where different wind power models are tested and compared. A two-mass model is used to model a constant wind turbine. The model consists of an asynchronous generator, a turbine, and a low speed shaft with a tensional stiffness. The model representing the variable speed wind turbine is based on a DFIG model included in the simulation software. The two-area network consists of two areas connected together through a long line between Bus 5 and Bus 6. Area 1 has two production sources, one placed in Bus 1 and one placed in Bus 2. The second area represents a large network modelled as a very large synchronous generator with a high inertia. The calculations have showed how modal analysis can be used to evaluate a system by using linearized differential equations and how the systems robustness against small disturbances can be altered by changing the systems parameters. Simulations have verified that a two-mass model must be used when modelling a constant speed wind turbine. The inertia of the turbine will greatly influence the model's behaviour and must therefore be included in the model. Eigenvalues analysis performed during different wind speeds have documented that wind power will not become less stable towards small disturbances when operated at low wind speed conditions.

With the recent developments in semiconductors and control equipment, Voltage Source Converter based High Voltage Direct Current (VSC-HVDC) has attracted the growing interest of researchers. The use of VSC technology and Pulse Width Modulation (PWM) has a number of potential advantages: short circuit current reduction; rapid and independent control of the active and reactive power, etc. With such highly favourable advantages, VSC-HVDC is definitely going to be a large part of future transmission and distribution systems. HVDC technology based on VSC technology has been an area of growing interest recently because of its suitability in forming a transmission link for transmitting bulk amount of wind power. This thesis deals with the control of VSC-HVDC. The objective of the work is to understand the control structure of the VSC-HVDC system, and establish the tuning criteria for the PI controllers of the converter controllers. A model of a VSC based dc link using PWM Technology is developed. A mathematical model of the control system based on the relationships between voltage and current is described for the VSC. A control system is developed combining an inner current loop controller and outer dc voltage controller. The vector control strategy is studied and corresponding dynamic performance under step changes and system fault is investigated in PSCAD/EMTDC simulation package. The simulation results verify that the model can fulfill bi-directional power transfers, fast response control and that the system has good steady state performance. The controller parameters tuned according to the developed tuning criteria is found to provide acceptable system performances.

The North Sea has a vast amount of wind energy with largest energy per area densities located about 100-300Km of distance from shore. Should this energy be tapped by offshore wind farms, HVDC transmission would be the more feasible solution at such long subsea distances. On the other hand Norwegian oil/gas platforms in the North Sea use electricity from gas fired turbines at offshore sites. These gas turbines have much less efficiency than onshore generation of electricity and also release large amounts of green house gases. Therefore supplying the platforms with power from onshore transmitted by HVDC will result in benefits both from economic and environmental protection perspectives. Given these two interests for HVDC in the Norwegian offshore, the use of Multiterminal HVDC (MTDC) is a potential solution for the integration of the wind farms and oil/gas platforms into the onshore grid system. Hence, this thesis focuses on the operation and control of MTDC systems. The MTDC system is desired to be capable of interfacing with all kinds of AC grids namely: stiff, weak and passive grid systems. Compared to the classical thyristor based converter, VSC has several features that make it the most suitable converter for making of MTDC, the most decisive being its ability of bidirectional power transfer for fixed voltage polarity. VSC-HVDC is also suitable for implementing control of active and reactive current in synchronously rotating d-q reference frame which in turn results in decoupled control of active and reactive power. In the first two chapters of the thesis literatures are reviewed to understand operation of VSC and its use in HVDC systems. Afterwards controllers are developed for different AC connections (stiff, weak and passive) and for different DC parameter (power, DC voltage) control modes. DC voltage and active power control are implemented by active current control and AC voltage and reactive power control are achieved by reactive power compensation. Tuning techniques for the PI controllers are discussed and used in the simulation models. Finally control techniques for reliable operation of MTDC are developed. In order to validate theoretical arguments, each of the control schemes was developed and simulated in PSCAD/EMTDC simulation software. Simulation results indicate that satisfactory performance of VSC-HVDC was obtained with the proposed active/reactive power controllers, AC/DC voltage controllers, frequency and DC overvoltage controllers. For coordinated multiterminal operation, voltage margin control method and DC voltage droop characteristic were used. These are control methods based upon realization of desired P-UDC characteristic curves of converter terminals. Four-terminal MTDC system with different AC grid connections was used to study the multiterminal operation. Simulations have shown that voltage margin control method results in reliable operation of MTDC during loss of a terminal connection without the need for communication between terminals. The use of DC voltage droop control along with voltage margin control enabled load sharing among VSC-HVDC terminals in DC voltage control mode according to predetermined participation factor.

Direct electrical heating (DEH) of pipelines is a flow assurance method that has proven to be a good and reliable solution for preventing the formation of hydrates and wax in multiphase flow lines. The technology is installed on several pipelines in the North Sea and has become StatoilHydros preferred method for flow assurance. Tyrihans is the newest installation with 10 MW DEH for a 43 km pipline. However, the pipeline represents a considerable single-phase load which makes the power system dependent on a balancing unit for providing symmetrical conditions. This limits the step out distance and is not suitable for subsea installation. Aker Solutions has proposed several specially connected transformers for subsea power supply of DEH systems, Scott-T being one of them. The Scott-T transformer is a three-to-two-phase transformer which provides balanced electrical power between the two systems when the two secondary one-phase loads are equal. By implementing this transformer, it can be possible to install the power supply subsea as there is no need for a balancing unit. In addition, the system may be applicable for long step out distances. This is because the pipeline is inductive and can use the reactive power produced by the long cable which also can increase the critical cable length. There are however some limitations on this system using the Scott-T transformer. There is a large variation in the magnetic permeability between individual joints of the pipeline. This can result in different load impedance of the two pipe sections connected to the Scott-T transformer. The result is unbalance in the power system. The method of symmetrical components is applied to investigate the behavior during unbalanced loading of the Scott-transformer. The relationship between the negative- and the positive sequence component of the current is used to express the degree of unsymmetry. For the simulations in SIMPOW, the Scott-T transformer is modelled by the use of Dynamic Simulation Language. The simulations on the DSL model give correct and reliable results for analysing the the degree of unsymmetry in the Scott-T transformer. When the load impedance of one pipe section is varied, simulation proves that it can change between 0.75 and 1.34 per unit of the other pipe impedance. The Scott-T transformer does still provide electrical power between the two systems which is below the limit for the degree of unsymmetry (15%). Case 1 and Case 2 introduce two possible configurations for a subsea DEH system with the Scott-T transformer implemented. The configurations include an onshore power supply which is connected to a subsea power system for direct electrical heating and a subsea load at the far end of the subsea cable. The pipeline in Case 1 is 100 km long and is divided into two pipe sections of 50 km which are connected to a Scott-T transformer. The pipeline in Case 2 is 200 km long and is divided into four pipe sections of 50 km each. There are two Scott-T transformers in Case 2. For normal operation of the subsea load (50 MW, cosfi=0.9) and heating the pipe content from the ambient sea emperature, the results indicate that tap changers are necessary to keep the Scott-T transformers secondary terminal voltage at 25 kV. This meets the requirement in both cases for heating the pipe content from 4 to 25 degrees celsius within 48 hours after a shutdown of the process. The degree of unsymmetry is zero for both cases when the system is operated as normal. However, all system simulations indicate that reactive power compensation has to be included for Case 1 as well as for Case 2 in order to have a power factor of unity at the onshore grid connection. The fault scenarios indicate that the degree of unsymmetry is dependent on both the type of fault and the power supply in the system. For Case 1, the relationship (I-/I+) is only of 3.3% in the subsea cable when there is a short-circuit at DEHBUS3, but as much as 87% at the grid connection. The degree of unsymmetry in the Scott-T transformer is then 67%. This is far beyond the limit for maximum negative sequence component of 15%. The significant unsymmetry in the line between the grid and BUS1 is most likely due to the large power delivered to the fault. During the fault, the reactive power delivered to the system increases from 10.6 Mvar to 131.9 Mvar after the fault, but the active power increases only from 75.2 MW to 87.1 MW. This means that it is most likely the reactive power that contributes to the consequent unsymmetry and negative sequence component of the current. There are two Scott-T transformers installed in Case 2. If the DEH system is only heating the pipe section closest to shore (at DEHBUS33), simulations show that the three-phase power system becomes unsymmetric which results in different phase currents. The degree of unsymmetry at the grid connection is 32% when only the pipe section at DEHBUS33 is heated. In addition, the unbalance in the three-phase system caused by SCOTT1 involves unbalance in the SCOTT2 transformer as well. The load voltages are not equal in magnitude and dephased of 90 degrees for this mode, but are 32 kV and 35 kV respectively and dephased of 88 degrees. This concludes a very important behavior of the Scott-T transformer. The simulations conclude that the Scott-T transformer provides symmetrical conditions for both configurations when the two load impedances are equal. However, Case 2 shows an important result when installing two Scott-T transformers in the same system. Unbalanced loading of one of the specially connected transformers gives unsymmetrical conditions in the three-phase system which results in unbalanced load voltages for the other Scott-T transformer. The analysis is limited to the configurations given for Case 1 and Case 2, but shows typical results when an alternative transformer connection is implemented in a DEH system.

There is an increasing amount of power processed through power electronics in the areas of generation interface, energy storage and loads. This increment enables possibilities for improved solutions for efficient generation and use of electric power. Traditionally loads in AC distribution systems have been seen as passive and individual elements rather than active components of the system. An AC distribution system with high percentage of power electronic loads can be susceptible for instability under abnormal operation conditions if the converter controls are not designed for such conditions. This thesis introduces a solution of reactive current control for a constant power load (CPL) in an AC distribution system. A CPL is a load that draws a constant amount of active power without regard to any drops in system voltage. The resistance seen from the AC distribution system to the CPL is known as a negative input resistance which is characteristic for this kind of load. A drop in AC system voltage will result in increased current and vice versa. Hence the resulting resistance will be negative. Negative resistance behaviour is not favourable for system stability and the work has focused on a control of the converter that reduces the instability effect of the load. By controlling the reactive current component to inject current for support of the AC distribution system voltage during faults and other interferences, the load becomes an active participant in the AC distribution system. An AC distribution system has been built in PSCAD/EMTDC. An asynchronous generator and a fixed capacitor are used as distributed generation. The CPL consists of an AC/DC converter and a voltage dependent current source in order to keep constant DC power at the load. Focus has been on the converter control implementing a voltage oriented vector control based on a two phase rotational reference frame. Measurements of current and voltage with different voltage drop levels have been done for comparison of a CPL with and without reactive current control. The simulation example has verified the negative resistance phenomenon of the CPL. Results shows that the AC system voltage is less vulnerable in case of faults if the converter control is designed to inject reactive current into the AC distribution system.

Offshore wind power has proven to be a renewable energy source with a high potential, especially in the North Sea, where an important development is going on. The location of the wind farms tends to move far from the coast to benefit stronger and more constant wind. In the same time, the power output of the wind farm is increasing to several hundreds of MW up to 1 GW. In the European liberalized electricity market, the interconnection of the countries become very important to facilitate the cross-border trade of electricity but also to improve the reliability of the grid. Combining this both aspects into one, a big offshore HVDC grid connecting countries and large wind farms spread allover the North Sea is currently being studied and developed. So in addition of the challenge given by a high penetration of the wind power production in the European power production scheme, new challenges are opened especially for the offshore transmission. This master thesis presents the integration to grid of a single 1 GW or a cluster of wind farms connected to an oil rig with different connection scheme based on HVDC transmission using the Voltage Source Converter (VSC) technology. The connection of the offshore wind farms is done either with a single HVDC transmission or two HVDC transmissions connected to the main grid at two different Points of Common Connection situated in the south-west of Norway. The wind farms are not represented in detail but by a single generator. They are equipped for the simulation with Double Fed Induction Generators (DFIG) to be representative of the reality, almost half of the wind turbines are today equipped with DFIG technology. Two disturbances are used to test the electrical stability of the system: a classical 150ms three fault phase in agreement with the grid code requirements on the ride fault through requirements and 100ms fault leading to the tripping of a line. The impact of using different types of generator is also investigated with the simulation of cluster wind farm where a wind farm is equipped with Fixed Speed Generator (FIG). The emphasis is put on the response of the VSC-converter and to a lesser extent on the behaviour of the wind turbine generator. It is demonstrated the capacity of the VSC-converter to stabilize a small grid alone and to “isolate” a disturbance. The voltage and the frequency offshore are practically unaffected by a fault onshore and vice versa. As expected, it is demonstrated that the multiplication of the VSC-HVDC converter in a grid improves the stability of the system. Finally, it has been noticed that there maybe some interactions if several different types of generators are used. The replacement of a generator by another type inside the wind farm cluster may change completely the dynamic behaviour after a disturbance. Simulations are performed with PSS/E.