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  • 1.
    Aguilera, Miguel
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Semantic and Physical Modeling and Simulation of Multi-Domain Energy Systems: Gas Turbines and Electrical Power Networks2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The ITEA3 OpenCPS (Open Cyber-Physical System Model-Driven CertifiedDevelopment) project focuses on interoperability between the Modelica/UnifiedModeling Language (UML)/Functional Mock-up Interface (FMI) standards, improved(co-)simulation execution speed, and verified code generation. The project aims to developa modeling and simulation framework for cyber-physical and multi-domain systems. Oneof the main use cases for the framework, is the multi-domain equation-based modelingand simulation of detailed gas turbine power plants (including the explicit equation-basedmodeling of turbomachinery dynamics) and the electrical power grid.In this work, UML class diagrams based on the Common Information Model (CIM)standard are used to describe the semantics of the electrical power grid. An extension basedon the standard ISO 15926 has been proposed to derive the multi-domain semanticsrequired by the models that integrate the electrical power grid with the detailed gas turbinedynamics.Furthermore, the multi-domain physical modeling and simulation Modelica language hasbeen employed to create the equation-based models of the use case of this project. Acomparative analysis between the Single-Domain and Multi-Domain model responses hasbeen performed both in time and frequency. The results show some interesting differencesbetween the turbine dynamics representation of the commonly used GGOV1 standardmodel and the less simplified model of a gas turbine.Finally, the models from each domain can be exchanged between two differentstakeholders by means of Functional Mock-Up Units (FMUs), defined by the FMIstandard. Promising test results were obtained with different simulation tools that supportthe standard, which demonstrates the feasibility of exchanging unambiguous multi-domainmodels with a detailed gas turbine representation. This shows the potential of the FMIstandard for manufacturers to exchange equation-based multi-domain models, while at thesame time protecting their intellectual property.

  • 2.
    Ahlfors, Charlotta
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    On the impact of wind power on CO2 emissions in a power system2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is carried out at KTH Royal Institute of Technology in Stockholmthe spring 2017. The project analyses the impact of wind power in a power system.A fictitious power system, created from the Nordic32 test system, is used for theanalysis. The power sources in the test system are hydro power, nuclear power, CHPand wind power, resembling Swedish conditions. The power production planning inthe system is solved as a mixed integer linear programming problem in GAMS withhourly resolution. From the result of the planning problem calculations of CO2emissions are carried out with Monte Carlo simulations. Different cases with differentamounts of wind power installed in the test system are studied via a stochasticMarkov model. The load model in the test system consists of hourly time seriesdata for a specific day. Furthermore, challenges with wind power as a continuouslyvarying power source are studied. These challenges are balance between productionand consumption in the power system, excess of power etc.The results show that increasing the wind power production results in a decreasein CO2 emissions. This can be seen from the different simulations in the project.However, the results show that increasing the wind power production means that thesystem becomes more sensitive to keep the power balance. Moreover, the dischargecapacity and the efficiency of the hydro power plants are important factors in thetest system.

  • 3.
    Ahmed, Zeeshan
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Analysis of Partial Discharge in OIP Bushing Models2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A high voltage bushing is a very important accessory of power transformers. Bushings are used to insulate high voltage conductors where they feed through steel tank of a power transformer. There are different sources of electric stress that may result in degradation of bushing. Partial discharges (PDs) are one of the main sources of electrical degradation. PDs occur due to defects in electrical insulations, and can lead to insulation failure. This thesis is composed of two parts. The first part deals with design of a 145 kV oil impregnated paper (OIP) bushing by using capacitive radial grading technique. In capacitive grading the foils of calculated length are placed at predetermined radial distance between the paper layers in order to distribute voltage and electric field uniformly between high voltage conductor and ground potential. A 145kV OIP bushing was designed according to dimensions of ABB GOE type bushing. After calculations, the 145 kV bushing geometry was modeled in COMSOL Multiphysics in order to analyze the voltage and electric field distribution in the bushing. In the second part of this thesis a scaled down model was designed using the capacitive radial grading technique. After designing, the scale down model was implemented in COMSOL in order to ensure that the voltage and electric field distribution should be similar to the full scale model of bushing. The scaled down bushing test model was made in laboratory by wrapping impregnated papers and foils on conductor tube according to calculated dimensions. These papers were impregnated with mineral oil. The test model was placed in an oil filled tube. Different defects were added in scale down bushing model and model was connected to PD measurement set up. PD inception voltage was measured and PD patterns were recorded on an insulation condition monitoring system (ICM). These patterns are analyzed in order to conclude about the signature of partial discharges in OIP bushings. From the PD pattern, the type and location of PDs can be concluded. PD patterns reveal that the main causes of PDs in OIP bushing can be gas filled cavities and surface discharges from foil edges.

  • 4.
    Al Karim, Miftah
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    PMU Data Mining in and analysis of suitable algorithm for fault pattern recognition.2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Phasor measurement unit (PMU) is getting much attention in recent days to acquire power system data. It is because PMU provides the opportunity to collect high resolution system. Having a high resolution data provides scopes to monitor a system with different computational methods. Data mining is one of the effective methods. In the age of power system automation high resolution power system data storage and management has become more feasible. Data mining can be implemented on high resolution PMU data and many advantages can be achieved from such an operation.  

    Data mining is a scientific process through which a knowledge or patterns are identified from a large amount of data base. Data mining in power system based on PMU data is getting much focus in the recent years. Some of the prominent research on mining power system data and finding pattern is already going on in this field.

    There are different pattern recognition algorithms deployed in data mining field. Research has also been done to check the efficacy of those algorithms in action.

    In this thesis implementation of existing pattern recognition algorithms based on background study is carried out. Along with it one work-process is proposed to check out the possibilities of data mining in power system regarding fault pattern recognition. The mining process proposed here is a mixture of different existing algorithms and a new algorithm for fault classification. The work here mostly offers a broad perspective of data mining in power system rather than dealing with a specific application.

  • 5.
    Amine Ramdani, Ahmed
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Rudnik, Sebastian
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Design and Construction of High Current Winding for a Transverse Flux Linear Generator Intended for Wave Power Generation2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There is currently a high demand for electric power from renewablesources. One source that remains relatively untapped is the motionof ocean waves. Anders Hagnestål has been developing a uniquelyefficient and simplified design for a point-absorb buoy generator byconverting its linear motion directly into alternating electric power usinga linear PM engine. To test this method, a smaller prototype isbuilt. Its characteristics present some unusual challenges in the designand construction of its winding.Devices of this type typically use relatively low voltage (690V typicallyfor a wind turbine, compared to the 10kV range of traditionalpower plants). To achieve high power, they need high current, whichin turn requires splitting the conductors in the winding into isolatedparallel strands to avoid losses due to eddy currents and current crowding.However, new losses from circulating currents can then arise. Inorder to reduce said losses, the parallel conductors should be transposedin such a way that the aggregate electromotive force the circuitsthat each pair of them forms is minimized.This research and prototyping was performed in absence of advancedindustrial means of construction, with limited space, budget,materials, manpower, know-how, and technology. Manual ingenuityand empirical experimentation were required to find a practical implementationfor: laying the cables, fixing them in place, transferringthem to the machine, stripping their coating at the ends and establishinga reliable connection to the current source.Using theoretical derivations and FEM simulation, a sufficientlygood transposition scheme is proposed for the specific machine thatthe winding is built for. A bobbin replicating the shape of the enginecore is built to lay down the strands.The parallel strands are then organized each into their respectivebobbin, with a bobbin rack and conductor funneling device being designedand constructed to gather them together into a strictly-organizedbundle. An adhesive is found to set the cables in place.Problems with maintaining the orientation and configuration of thecables in the face of repeated torsion are met and solved. A chemicalsolution is used to strip the ends of the conductors, and a reliableconnection is established by crimping the conductors into a bi-metalCu-Al lug.ivIn conclusion, the ideal transposition schemes required to cancelout circulating currents due to magnetic flux leakage are impossibleto put in practice without appropriate technological means. The feasibletransposition scheme turns out to be a simple mirroring of conductors’positions, implemented by building each half of the windingseparately around replicas of the core and then connecting them usingcrimping lugs.

  • 6.
    Andersson, Karl-Johan
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Komponentuppdelning av elnätetpå lokalnivå2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Sweden will, in accordance with the EU-directive 2003/54/EC, move from post-regulating the electricity power grid-tariffs by using a fictitious grid, to a regulation in advance which uses the actual power grid as a starting point. For this purpose a component breakdown of the grid needs to be made to determine the value of the network and by that the tariff price that is reasonable for the network business in question to charge.

    The primary breakdown criteria is the voltage-level and type of region. Voltage-level is crucial for the cost and complexity of a grid-part, because the higher the voltagelevel is, there are more and stricter laws and rules to follow. This work is limited to the distributionpart of the grid, in other words voltage levels from 20 kV and below.

    The type of region is crucial to the type of components you can and want to use. In city environments both overhead-wires and independent substations are undesirable for both practical, safety and aesthetic reasons. Overhead-wires is more common in rural areas, where it´s not economically justifiable to use ground-cable, so the cheaper air-alternative is chosen. An interference in a city environment is also much more costly than one in a urban or rural setting, which is crucial for a component's value. The value of an existing substation in a city environment is much higher than a station of similar nature in the countryside.

    The components that are taken into account are overhead-wires, ground-cables and substations. These come in a variety of aberrations that are used as preconditions for the grouping of components.

    Based on the components actual presence in the network and their electrical properties they are divided into groups, which together with type of region and voltage-level can determine the component's actual value and thus be able to give a value to the power-grid in question.

  • 7.
    Asadullah Siddiqui, Makhdoomzada
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Theoretical investigations of stator iron losses in a 15 MW induction motor equipped with fractional conductor windings2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Iron loss calculation in AC machines has aroused great interest over the years, in an attempt to make electrical machines more efficient. However, different iron loss models yield different results for the same machine, owing to their individual limitations. This element of uncertainty associated with obtained values is further enhanced in cases where knowledge of the flux density’s behavior is very elementary.  This thesis gives an overview of different iron loss models and applies them to a 15 MW induction motor equipped with fractional conductor winding. The aim is to analyze the results acquired using various models and determine the suitability of the investigated models. The two main categories of iron loss models implemented are the Steinmetz models and the loss separation model. Iron loss results confirmed that the basic Steinmetz equation is only suitable for sinusoidal flux density waveforms and its accuracy diminishes as the waveform becomes increasingly non-sinusoidal. Furthermore, parts of the stator where the magnetic field is most rotational were identified as the roots of stator teeth. However, rotational magnetic fields were found to have a small effect on stator yoke iron losses.

  • 8.
    Axente, Iurie
    KTH, Superseded Departments, Electric Power Systems.
    Belastningsfördelning i kommplex form: En ny metod för analys av stabiliteten i stationära tillstånd2002Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 9.
    Babazadeh, Davood
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Modeling of Wide Area Monitoring System as a Cyber Physical System2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Operating the large-scaled electric power grid closer to parameters limit as a solution to restriction on transmission lines expansion, or electrical marketing issues such as reregulation which brought the connection of national grids to surrounding neighbor’s grid may make the control of the power system more complicated than before. In this situation, technologies like PMU-based Wide Area Monitoring and Control System are developed to improve the monitoring of power grid across large geographic areas and accordingly controlling grid in more efficient and intelligent way. WAMC system bring a new opportunity for applications in terms of data availability, accuracy and high sampling rate which in turns cause applications to improve or re-design their algorithms. In order to have confidence on correctness, performance and reliability of WAMC applications in real world scenarios, a pseudo-real test bed of whole WAMC system which mirrors the characteristic of both communication and power systems as real as possible seems to be required for designing/testing such applications. The purpose of this study is to put effort on proposing and developing a WAMC testing platform to facilitate the real time emulation of the dynamic power grid, the ICT infrastructure that overlays the grid and WAMS applications. The proposed platform consists of OPNET as a powerful communication simulator/emulator which is connected to Power Simulator (SIMULINK) on one side, and connected to end point stations such as PDC or application on the other side through OPNET’s real-simulation gateway called SITL. As an assessment to performance of developed platform architecture, different scenarios has been carried out to find out the effects of communication protocols i.e. UDP and TCP on network metrics such as data delay.

  • 10.
    Baudette, Maxime
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Fast Real-time Detection of Sub-Synchronous Oscillations in PowerSystems using Synchrophasors2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Recent concerns about the environment have resultedinto large investments in renewable energies for electricityproduction, especially wind power. The integration of renewablesources of energy raises however several problemswhich have not yet been completely understood nor studied.Oscillatory events around 13 Hz have been recorded inthe US by Oklahoma Gas & Electric (OG&E). Such a highfrequency is very different from the traditional and wellstudied Inter-area oscillations, it is also beyond the measurementcapabilities of most of the existing measurementequipments and monitoring tools.

    This Thesis focuses on the development and implementationof algorithms for oscillation detection which can supportreal-time monitoring tools. It proposes a real-timemonitoring tool that exploits synchronized phasor measurementsfrom PMUs, which allow real-time analysis of higherfrequency events, filling the lack of such monitoring applicationin the power systems area. This tool was built as aprototype for real-time applications which utilize real-timePMU data for enhanced monitoring and control of powergrids.

  • 11.
    Bergman, David
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    The Effect of Partial Discharge Aging on the Dielectric Response of Polymers2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This work investigated the effect of partial discharges (PD) on the complex permittivity

    of PVC, PC, PTFE, PE and PA6. The material samples were subjected to prolonged

    PD activity and the complex permittivity of the material was measured by dielectric

    spectroscopy (DS) before and after the sample was aged. The results showed a change

    in the loss factor for the tested materials, some were more affected than others and

    showed different behaviors when subjected to the PD aging. Hence it was not possible

    to find any general trend in the complex permittivity of the tested materials. Several

    of the materials exhibited a loss factor with -1/2 slope at low frequencies corresponding

    to diffusion. The -1/2 slope implies that the loss factor and the dynamic component of

    the real permittivity should be equal, which could not be seen. Therefore it is uncertain

    whether what was observed is a diffusion process or not. The results could suggest that

    PD aging causes a change in the trapping characteristics of the material. Furthermore,

    space charges deposited on the cavity wall from the PD activity could diffuse into the

    bulk of the material where some of the charges are trapped. If a DS measurement

    is performed before the trapped charges have had time to recombine or be conducted

    away, it could affect the complex permittivity. This was demonstrated by performing

    another DS measurement on an aged PC sample which had been left to rest for 35 days.

    The measurement showed that the complex permittivity had returned to almost the

    same state as before aging. Measurement problems were encountered which affected the

    measurements in this work. The problems are believed to be caused by the measurement

    electrodes used for the DS measurements not being heavy enough to eliminate small

    unwanted air-gaps between the electrodes and sample. Furthermore, incomplete results

    were obtained for some measurements which was believed to be due to the capacitance of

    the sample being at the limit of what the measurement instrument was able to measure.

  • 12.
    Bergström, Mats
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Customer Outage Reduction Using AMR Data2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Due to a new law that enforces distribution companies to install AMR (Automatic Meter Reading) meters, new possibilities are opened. Not only the primary purpose of AMR meters, i.e. measure the consumption at the customer side, can be beneficial but also outage management which can help reduce the unavailability of a grid. These meters have been further developed lately and new areas of use are under investigation.

    Distribution automation is a term that normally connects to middle voltage level substations. This technology is used to monitor and remotely control power distribution, where for example outage management is an important part. Historically, implementation of distribution automation at low voltage level has never been interested since investments have been given priority to middle voltage level which covers more customers.

    This thesis investigates the possibilities to use AMR meters in order to reduce customer outages, identify limits in present construction and suggest necessary modifications to improve the performance of the system. A reliability analysis of the different proposed solutions and a sensitivity analysis of the most attractive solution are also included. An investment analysis is performed, to get an idea how much the investment would cost on an implementation The result from the thesis has shown, that one of the proposed solutions which consists of a number of breakers implemented strategically in a grid, not contribute to any major improvements. The investment cost is relatively high, and the reliability analysis has shown that the amount of outages increase, while the average repair time of interrupted customers decrease. If the breakers are less expensive and their fault rate reduced, a new investigation may be of interest in the future.

  • 13.
    Bergsåker, Claudia
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Impact of transformer core size on the reactive power requirement of power transformers due to GIC2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Geomagnetically induced currents (GIC) are a natural phenomenon which arises due to solar

    storms. During a solar storm, large amounts of magnetized plasma are ejected from the surface

    of the sun. When this plasma reaches earth, it causes fluctuations in the geomagnetic field. Such

     fluctuations may induce DC over-currents in long transmission lines. These currents affect the

    transmission system several dierent ways; In particular high voltage transformers are sensitive to

    GIC. When the over-current flows through the transformer windings the reactive power absorption

    of the transformer increases, which may lead to voltage instability in the power system. For this

    project, the main issue has been to determine whether or not an increase in the size of the transformer

    core leads to the reactive power absorption being less sensitive to GIC. In order to investigate

    this issue a recently developed transformer model has been used; the Hybrid transformer model.

    This model combines the principle of duality with a matrix representation of the transformer. The

    Hybrid transformer model, which has recently been implemented in the power system simulations

    software PSCAD, has been used to simulate GIC events in transformers of varying core sizes. The

    results from these simulations indicate that a larger transformer core is associated with a smaller

    increase in reactive power absorption during a GIC event. It is also clear that the reactive power

    absorption as a function of GIC magnitude is a non-linear function when the Hybrid transformer

    model is applied. This function has previously been considered a linear function.

  • 14.
    Björk, Erik
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Load Characteristic Influence on Power Oscillation Damping: Case Study on HVDC-interconnected AC-Grids2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The increasing share of renewables in the electric grid may have a negative impact on the systemstability to which conventional control methods are insucient. The report focuses on the stabilityof low frequency inter-area modes. Along the development of renewables, power electronics aremore frequently used between the actual load and the grid. Hence the characteristics of the loadsis undergoing a change as well. This report investigates how dierent load characteristics inuencethe damping in the grids. The investigation is performed by a simulation experiment where a modelconsisting of two AC-grids interconnected via an HVDC-link is implemented in two simulation softwareprograms, PSCAD and Simulink. The HVDC-link has an implemented active power oscillationdamping control to improve the damping of the overall system. The report also review which softwarethat is most suitable for the given investigation. It is shown that active power loads contributesto the damping best if they are modelled as constant impedance loads and less for constant powerloads. Reactive loads with inductive behaviour contributes to the damping best if they are modelledas constant power loads and contributes least if they are constant impedance loads. The evidencesuggest that the damping provided by the loads is uncorrelated with the damping provided by theHVDC-link. The simulation software that suited the author's preference best was Simulink. Theseresults contribute to the understanding of how loads inuence the system damping and can be usedin future studies, where it is interesting to know if the load damping is over or underestimated.

  • 15.
    Borquez Caballero, Rodrigo Edgardo
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Calculating the Distance to the Saddle-Node Bifurcation Set2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A power system will experience voltage collapse when the loads increase up to a certain critical limit, where the system physically cannot support the amount of connected load. This point identified as a Saddle- Node Bifurcation (SNB), corresponds to a generic instability of parameterized differential equation models and represents the intersection point where different branches of equilibria meet. At this point the jacobian matrix of the system is singular and the system loses stability bringing the typical scenario of voltage collapse. To prevent voltage instability and collapse, the computation of the closest distance from a present operating point to the saddle-node bifurcation set can be used as a loadability index useful in power system operation and planning. The power margin is determined by applying the iterative or direct method described in [16]. Numerical examples of both methods applied to IEEE 9-bus system and IEEE 39-bus system shows that the iterative method is more reliable although it requires a longer computation time. The stability of the system is negatively affected in two ways when generators reach their reactive power limits: the voltage stability margin

    is deteriorated, or immediate voltage instability and collapse is produced.

  • 16.
    Bourchas, Konstantinos
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Manufacturing Effects on Iron Losses in Electrical Machines2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis, the magnetic properties of SiFe laminations after cutting and welding

    are studied. The permeability and the iron loss density are investigated since they are

    critical characteristics for the performance of electrical machines. The magnetic measurements

    are conducted on an Epstein frame for sinusoidal variations of the magnetic ux

    density at frequencies of 50, 100 and 200 Hz, according to IEC 404-2. Mechanical cutting

    with guillotine and cutting by means of ber and CO2 laser are performed. The inuence

    of the ber laser settings is also investigated. Especially the assisting gas pressure and

    the power, speed and frequency of the laser beam are considered.

    In order to increase the cutting e ect, the specimens include Epstein strips with 1,

    2 and 3 additional cutting edges along their length. It is found that mechanical cutting

    degrades the magnetic properties of the material less than laser cutting. For 1.8% Si

    laminations, mechanical cutting causes up to 35% higher iron loss density and 63% lower

    permeability, compared to standard Epstein strips (30 mm wide). The corresponding

    degradation for laser cut laminations is 65% iron loss density increase and 65% permeability

    drop. Material of lower thickness but with the same Si-content shows lower

    magnetic deterioration. Additionally, laser cutting with high-power/high-speed characteristics

    leads to the best magnetic characteristics among 15 laser settings. High speed

    settings have positive impact on productivity, since the cutting time decreases.

    The inuence of welding is investigated by means of Epstein measurements. The test

    specimens include strips with 1, 3, 5 and 10 welding points. Experiments show an iron

    loss increase up to 50% with a corresponding 62% reduction in the permeability.

    A model that incorporates the cutting e ect is developed and implemented in a FEMbased

    motor design software. Simulations are made for a reference induction motor.

    The results indicate a 30% increase in the iron losses compared to a model that does

    not consider the cutting e ect. In case of laser cut core laminations, this increase reaches

    50%. The degradation prole considers also the deteriorated magnetizing properties. This

    leads to increased nominal current up to 1.7% for mechanically cut laminations and 3.4%

    for laser cut la

  • 17.
    Boyra, Jon
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    State of the art of actual pitch systems and analysis of electrical pitch systems for wind turbines2007Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 18.
    Brandt Lundqvist, Olof
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Construction of an Active Rectifier for a Transverse-Flux Wave Power Generator2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Wave power is an energy source which could make a decisive difference in thetransition towards a more sustainable energy sector. The growth of wave powerproduction has however not been as rapid as the growth in other renewableenergy fields, such as wind power and solar power. Some technical obstaclesremain before a major breakthrough for wave power can be expected. Oneobstacle so far has been the low voltages and the resulting high power lossesin many wave power plants. A new type of wave power generator, which hasbeen invented by Anders Hagnestål at KTH in Stockholm, aims to solve theseproblems. This master’s thesis deals with the power electronic converter systemfor Anders Hagnestål’s generator. It describes the planning and constructionprocess for a single-phase AC/DC converter, which will eventually be a partof the larger converter system for the generator. A control system based onhysteresis current control is planned and assembled. The finished single-phaseconverter shows agreeable results working as an inverter, generating a distinctlysinusoidal AC voltage. However, some additional construction and calibrationin the digital control system remain, before the converter can be used in thepower conversion for a wave power plant.

  • 19.
    Brask, Martin
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    MODELLING OF THE POWER SYSTEM OF GOTLAND INPSS/E WITH FOCUS ON HVDC LIGHT2008Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose with this project is to develop a model of the whole power system of Gotland in the power system simulation software PSS/E. A model of the whole power system of Gotland has earlier been used in the power system simulation software Simpow but now there is a need to develop a model in PSS/E.

    In the power system of Gotland there are several components that need to be modelled such as lines, loads, transformers, shunt impedances, synchronous machines, asynchronous machines, an HVDC Classic link and an HVDC Light link. These components are modelled in the Simpow model and needs to be converted to the PSS/E model. The aim is to develop a model in PSS/E that is as equal as possible to the model in Simpow. Especially the HVDC Light link at Gotland has been investigated in the project.

    A problem with converting data from Simpow to PSS/E is that the models of several components differ in Simpow and PSS/E. Lines and shunt impedances can be modelled in the same way but the models for loads, transformers, synchronous machines, asynchronous machines, the HVDC Classic link, and the HVDC Light link differ in Simpow and PSS/E. The models in Simpow are converted to the models in PSS/E in an as equal way as possible. The results in PSS/E are analyzed and compared with the Simpow model.

    In the project we have also made a test of fault simulations in time-domain simulations in PSS/E. The aim with this test is to verify the PSS/E calculations when a three-phase or a single-phase fault is applied. The reason for that is that PSS/E only calculates using positivesequence components and therefore only is able to calculate exact during circumstances of symmetrical loads and faults. The result shows that the calculations for both symmetrical and unsymmetrical faults in PSS/E are correct concerning the positive-sequence components. A drawback in PSS/E is, however, that we do not have any information concerning the negativeand zero-sequence  components, which results in that we cannot calculate the three phasequantities. 

  • 20.
    Briggner, Viktor
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Design and comparison of PMaSynRM versus PMSM for pumping applications2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis aimed to design a permanent magnet assisted synchronous reluctancemachine (PMaSynRM) rotor for pump applications which were to be implemented inan existing Induction Machine stator. The machine were to be compared with a similarpermanent magnet synchronous machine (PMSM) with similar torque production in termsof cost and performance.This thesis goes through the theory of the Synchronous Reluctance Machine andthe Permanent Magnet assistance. A rotor was designed by utilizing existing design approachesand simulation of performance by use of finite element analysis. A demagnetizationstudy was conducted on the added permanent magnets in order to investigate thefeasiblity of the design.The final design of the PMaSynRM was thereafter compared to the equivalentsurface-mounted PMSM in terms of performance and cost. The performance parameterswas torque production, torque ripple, efficiency and power factor. Due to the lower torquedensity of the PMaSynRM, for equal torque production the PMSM had a 40% shorterlamination stack than the PMaSynRM.The economic evaluation resulted in that when utilizing ferrite magnets in the PMa-SynRM it became slightly cheaper than the PMSM, up to 20%. However, due to the fluctuatingprices of NdFeB magnets, there exist breakpoints below which the PMaSynRM isin fact more expensive than the PMSM or where the price reduction of the PMaSynRMis not worth the extra length of the motor. However, it was shown that the PMaSynRMis very insensitive to magnet price fluctuations and thereby proved to be a more securechoice than the PMSM

  • 21.
    Chen, Chen
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Simulation, design and experimental validation of a passive magnetic damper for ultra-fast actuators2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A contact system driven by a high energetic Thomson actuator requires to be decelerated from

    full speed down to zero. The forces originated from the interaction between a stationary

    copper tube and a moving array of magnets combined with plastic or ferromagnetic material

    are used to generate eddy-current damping. Five different configurations of small but strong

    (N52) neodymium magnets and spacers were benchmarked for simple free-fall damping. A

    comparison between experimental results and simulations (using COMSOL) has shown that

    the most effective damping is reached by two consecutive permanent magnets with opposite

    magnetization directions ,separated by low-carbon content steel concentrators(SN - Fe

    concentrator- NS).

    The proposed damper design is the result of the balance between various parameters such as

    magnet orientation topology in the array, spacer material and its dimensions, copper tube

    thickness and the air gap between copper tube and array.

    Furthermore, the design was scaled up and an actuator-drive system was added to perform

    more realistic tests, which demonstrated the damping effectiveness on a fast moving armature

    actuated by a Thomson coil energized by a capacitor bank. All models in the simulation

    predicted the damping effect in advance. Investigations were conducted with two cases: (1) A

    solid copper rod was supposed to pass through the magnet array; (2) A plastic shaft was

    applied to support the magnet array.

    Finally a damping prototype with a plastic shaft was built for completing damping tests. The

    results of these tests validated the numerical model with a high degree of accuracy.

  • 22.
    Chen, Cheng
    KTH, School of Electrical Engineering and Computer Science (EECS).
    The Impact of Voltage Dip Characteristics on Low Voltage Ride Through of DFIG-based Wind Turbines2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In last decade, there is a large increase in installed capacity of wind power. Asmore wind power is integrated into utility networks, related technologychallenges draw much attention. The doubly fed induction generator (DFIG) isthe mainstream choice for wind turbine generator (WTG) in current market andthe object of this thesis. It is very sensitive to voltage dips. The enhancement oflow voltage ride through (LVRT) is one of the most important issues for DFIG,and many works have already been done to provide solutions.In current works, the voltage dip waveforms that are applied in LVRTrelated works are largely different from waveforms in reality, because they failto consider the the effect of realistic wind farm configurations on waveforms ofvoltage dips and significant influences of additional characteristics of voltagedips. The true impact of the voltage dip needs to be assessed in performanceevaluation and development of LVRT methods. To support the development ofpractical LVRT capacity enhancement solutions, the application of voltage dipknowledge is definitely demanded.In this thesis, the characteristics of realistic waveform voltage dips in windfarm are analyized based on voltage dip knowldege from power quality field,measured voltage dip from industry and realistic wind farm configurations.Classical analysis theory is applied to explain the principles of the impact ofvoltage dip characteristics on dynamic behavior of DFIG. The impacts of manywidely neglected characteristics such as phase angle jump (PAJ), point on wave(POW) of initiation and recovery, voltage recovery process, transformerconfigurations, load effect are revealed and verified by simulations. The impactof many voltage dip characteristics on DFIG are studied for the first time.

  • 23.
    Chen, Zhenwei
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Virtual Power Plant Simulation and Control Scheme Design2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Virtual Power Plant (VPP) is a concept that aggregate Distributed Energy Resources (DER) together, aims to overcome the capacity limits of single DER and the intermit-ted natural characteristics of renewable energy sources like wind and solar. The whole system can be viewed as a single large-capacity power plant from the system‘s point of view.

    In this project, the literature review of VPP concept, architecture, existed project and the survey of VPP in Sweden are being conducted first. Secondly, the simplified VPP model is built on MATLAB/Simulink software. The simplified system contains a wind farm, a hydro power plant, a dynamic system load and an infinite bus representing the large transmission grid. During the simulation process, the generation and consump-tion unites are running according to the real history data located in external database. In the third place, optimized control schemes for the hydro unit in VPP model to decrease its effects on transmission grid are implemented in Simulink model. At the same time, hydro turbine should be controlled in an optimized way that without large turbulence. Basically, the hydro power plant is responsible for balancing the active power between the wind farm and dynamic load. Since there is a limit for the hydro turbine output, the rest of either power shortage or surplus power need to be com-pensated by the grid. This is the fundamental control scheme, so called run time con-trol scheme. The advanced control schemes here are based on the moving average control method and forecast compensation control method. The forecast compensa-tion control method use the 24 hours ahead load forecasting data generated by Artifi-cial Neural Network. Later on, analysis of those three control schemes will be pre-sented. The last part of the project is the conclusion of the different control schemes according to comparison of their control results.

  • 24.
    Cheng, Jialu
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Broadband Dieletric Properties of Impregnated Transformer Paper Insulation at Various Moisture Contents2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The actual life of a transformer is determined by ageing of the cellulosic insulation such as transformer paper. The presence of moisture in the insulation system decreases the electrical strength of paper and accelerates the aging. It is an efficient way to monitor the moisture content in paper insulation by measuring the dielectric constant of the paper. The moisture dependent permittivity of impregnated transformer paper below 1 MHz has been widely investigated. High frequency (> 1 MHz) dielectric spectroscopy is under requirement since the loss peak information is missing. The impregnated paper is kept in desiccators with saturated salt solutions to get the samples with moisture content from 1 % to 5.5 %. Then they are placed in a coaxial line and the scattering parameters are obtained by modern Vector Network Analyzer. Full wave analysis is utilized to calculate the permittivity from the obtained S-parameters due to its high accuracy. The magnitude of the dielectric spectroscopy below 100 Hz is very dependent on the moisture content while there is a horizontal shift of curves towards higher frequencies depending on the water content over a wide frequency range. The loss peaks appear between 1 MHz and 1 GHz for the impregnated paper with moisture level less than 5.5 %. Due to the limited system accuracy, there is a blank frequency band from 1 MHz to 100 MHz.

  • 25.
    Cofre Osses, Aliro
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Construction and Design of a Switch-Mode Converter for a TFPMSM in Wave Power Application2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Established climate changes and increasing regulations on fossil fuels makes it important toexplore different options for electric power generation from renewable energy sources. In 2015Sweden had the highest proportion of renewable energy in the European Union and electricitygeneration contributes the most to the proportion of renewable energy. An interestingopportunity to a further improvement on the number of renewable energy sources is wavepower. Wave power is based on the conversion of energy available in the motion of the wavesto electric power. Electric power generation from wave power plants has been studied since1970 and the major obstacles for its development have been the high costs of the plants and lowefficiencies. The KTH researcher PhD Anders Hagnestål, has developed a new type of wavepower generator with significant improvements on the machine’s efficiency. This master thesisdeals with the electrical energy conversion of the electric power provided by the generator. Thedesign and construction of single-phase switch-mode converter used for the electricalconversion AC/DC and DC/AC of the generated electric power is discussed and explained. Theconstructed single-phase converter showed a good electrical design. Nevertheless, importantimprovements are needed in the operating speed of the used microcontroller.

  • 26.
    COUCKUYT, LORENZ
    KTH, School of Electrical Engineering (EES), Industrial Information and Control Systems.
    Demand Response in Active Distribution Networks using integration of Network Manager and Aristo2013Independent thesis Advanced level (degree of Master (Two Years)), 10 HE creditsStudent thesis
    Abstract [en]

    As distribution and transmission grids have to become more and more ’active’, in order to increase performance and economic profitability, control is getting more complicated. Therefore an integration of a network control system and a power system simulator would be useful for analysis and training of operators having to adapt to a new way of controlling the grid.

     This thesis describes the technical implementation work performed to successfully create such an application: an integration of Network Manager and Aristo. Network Manager, created by ABB Ventix, is a network control center package, including SCADA. Aristo, created by Svenka Kraftnät, is a power system simulator for training purposes. Both systems are integrated using two modern standards: OPC UA and CIM. CIM is used to import the Svedala model from Aristo to Network Manager. OPC UA is used to integrate both programs in real time and provides communication of measurements, statuses and commands between both systems. CIM is used to export the Svedala power system model from Aristo to the databases of Network Manager. A local controller, optimizing the control of parallel transformers in substations, has been programmed in JACK. This local controller was also integrated in the system as a proof of concept.

     Our integrated Network Manager-Aristo platform can in the future be used in the ongoing research for better control strategies of grids by adding different local controllers and running different simulation scenarios.

  • 27.
    Croce, Pierre
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Evolution of the LV Network2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Providing reliable electricity to everyone is a very important matter nowadays. Both thetransmission system operator and the distribution system operator are acting on the grid inorder to insure it. The latter sometimes has to deal with problems regarding the voltage,especially in rural areas. Those issues are crucial because they might lead to a bad functioning ordamage some appliances, so they lower greatly the quality of supply. Moreover, the installationof new small producers such as wind power plants and solar panels to this network hasworsened the situation by complicating and multiplying the constraints. New methods are thusneeded to bring more flexibility to the distribution grid and consequently solve the voltageproblems and possibly others.The aim of this project was to test possible solutions to voltage problems in the lowvoltage network which is the part of the distribution grid directly connected to the finalconsumers. The main ones were the use of an on-load-tap-changer, capacitors and the controlof the producers connected at this level. At first, statistical models for the loads and theproducers were developed. The simulation itself was then designed and programmed. It isbased on Monte Carlo using a load flow procedure and takes into account a 30 years evolutionof the network. Finally, many cases were run to observe various behaviors and the mostinteresting ones were selected for the conclusions.The results showed that the on-load tap-changer is the possibility that adds the mostflexibility to the system and seems thus the best option due to the high randomness of theevolution of such networks. The other options tested are efficient in specific cases and cheaperso they might be interesting when it is possible to forecast the new customers and producers ofthe area, which is unfortunately not often the case. Finally, the negative effect of unbalance onsuch networks has been highlighted and it would be very good idea to develop procedures ableto give the best repartition of consumers among the phases at every bus in order to optimizeparameters such as voltage and losses.

  • 28.
    Crosara, Alessandro
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Calculating the Risk of Power Shortage in the Nordic Power System2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the near future, the decommissioning of large power plants is planned in the Nordicelectric power system, due to environmental and market reasons. This will be counteredby an increase in the wind power installed capacity, as well as by signicant investmentsin the transmission system. In such a context, characterized by several changes, theNordic power system might face reliability challenges.This thesis aims to calculate the risk of power shortage in the dierent price areas whichconstitute the Nordic power system, for three dierent scenarios: a base scenario 2015,scenario 2020, and scenario 2025. Dierent case studies, focusing on the Nordic powersystem and on some of its subsystems, are investigated. The reliability evaluation whichis carried out follows a probabilistic approach, by means of Monte Carlo simulations.Crude Monte Carlo, as well as an advanced variance reduction technique { namely Cross-Entropy based Importance Sampling (CEIS) { are applied and compared. An alternativesampling method based on stratied sampling is presented too.The starting point of this thesis is Viktor Terrier's 2017 Master thesis, \North EuropeanPower Systems Reliability" [1]. Model-wise, among the other improvements, load andwind power are sampled in a dierent way to account for the correlation between them.Data-wise, more realistic assumptions are made and more accurate data are used, thanksalso to the collaboration with Sweco Energuide AB, Department of Energy Markets.From the model perspective, it is concluded that CEIS outperforms crude Monte Carlowhen simulating small to medium size systems, but it cannot be successfully appliedwhen simulating large and very reliable systems like the Nordic system as a whole. Thepresented alternative sampling method can however be used for such cases. From thenumerical-results perspective, the drawn conclusion is that the Nordic power system isestimated to become more reliable by years 2020 and 2025. Even if partly intermittent,more generation capacity is expected to be available, and thanks to the signicant investmentswhich are planned in the transmission system, it will be possible to eectivelytransmit more power where needed, regardless of the area where it has been generated.The thesis is carried out at KTH Royal Institute of Technology, Department of ElectricPower and Energy Systems, in collaboration with Sweco Energuide AB, Department ofEnergy Markets, within the frame of the North European Energy Perspectives Project(NEPP).

  • 29.
    Damström, Julia
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Life cycle cost analysis of lithium ion batteries using different charging strategies: case study Stockholm Arlanda airport2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To reach existing climate goals, the transportation sector need to be readjusted. One alternative is to use electricityas fuel. A positive trend is that the market share of electric vehicles is increasing, much thanks to that the ba�eryprices are decreasing. One ba�ery that is commonly used in electric vehicles is the lithium ion ba�ery (LIB), whichprice has decreased and is expected to continue to decrease. One useful tool when investigating the costs is lifecycle cost (LCC) analysis.One goal of this master thesis is to perform a systematic literature review on existing research about LCC analysison LIB. �e literature review results show that the found, existing research mainly focuses on LIBs and life cycleassessments. �e focus on LCC analysis is concluded to be small, based on the found published literature.�e main goal of this project is to investigate the charging strategy impacts on LIB lifetime from an LCC perspectiveduring a 20 year period. �e investigated charging strategies are slow, fast and induction charging. Depending onhow a ba�ery is charged, di�erent lifetimes may be obtained which is why these strategies are investigated. �eLCC analysis includes and discusses the investment cost, preventive maintenance cost, corrective maintenance costand the residual value. �e aging of the LIB is examined using a ba�ery block in Simulink/MATLAB. �e ba�erymodel and LCC analysis is applied on a mail truck at Arlanda airport and uses therefore inputs from the mail truckto model for example the discharging pa�ern.�e results from the Simulink aging model show that depending on which charging strategy that is used, di�erentlifetimes are achieved for the same LIB.�e results also show that the lifetime of the LIB is strongly a�ected by thecharging current and the SOC limits. Induction charging gives the longest lifetime, 9.4 years, while fast charginggives the shortest lifetime, 7.7 years for an ambient temperature of 20

  • 30.
    De Lima, Francisco
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Power System Protection Modelling with IEC 61850 and IEC 614992019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The nature of the power system is changing; what was once a clearlydened generation-transmission-distribution-consumer power ow is nowshifting towards a distributed infrastructure, with great amounts of variablerenewable sources in the system. The penetration of alternative energieslike solar and wind have represented a game changer for the electricpower industry, diminishing the traditional dominance of fossil fuel basedsources, and moving towards a more renewable mixture. All this wasmade possible due to severe climate regulations, both in the Europeanand global framework, as well as ever decreasing installation, operationand maintenance costs for these novel technologies.However, the penetration of renewable energies brings challenges to thereliability and stability of the power system, which must be tackled accordingly.Fortunately, the tools are there, standards like the IEC61850 andIEC61499 were independently designed, and for dierent purposes. TheIEC61850 standard strives for inter-operability and vendor-independencewithin the substation design eld, specically in regards to the data objectsexchanged between the devices. On the other hand, the IEC61499standard is used for the design of industrial distributed systems.This report aims to answer the question: is it possible to generate anIEC61499 description which complements an IEC61850 substation speci-cation? To this end, an IEC61850-IEC61499 interface was created, whichtakes an IEC61850 substation specication description, as well as a seriesof conguration les (rules, connections, allocation, parameters) andgenerates extended descriptions of the substation, as well as a fully operationalIEC61499 system specication. This can be directly imported inthe 4DIAC tool, and executed to evaluate the performance of the designedprotection systems, in a network of distributed or centralized devices.A series of test cases were evaluated, and the obtained results demonstratethat it is possible to bridge the gap between IEC61850 and IEC61499,thus enabling power system engineers to assess the performance of a certainprotection scheme, before actually implementing it in the substation.This potentially reduces human errors and development times. The interfacewas implemented in Java p.l. and is distributed as an open sourceproject.

  • 31.
    Duenas Solis, Jose Luis
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Uppskattning av nollföljdsimpedansen hos trefas krafttransformatorer med utjämningslindning2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An important comission for Svenska kraftnät (SvK) as the Swedish authory in charge of the power distribution network is to operate the grid in the most efficient way. In order to ensure 99,9% uptime, constant maintenance and fault diagnostics are required for the entire network of which power transformers are an important component. The zero-sequence impedance is a way to determine the maximum fault currents a transformer can accept before being damaged. The zero- sequence impedance is one of three sequences used to analyze three-phase systems and is a quantity which is not easily obtained analytically. Its value is usually determined in tests carried out during the fabrication process. This information is not available for several transformers currently in service on the power grid.

    The focus of this thesis is to develop empirical models to estimate the value of the zero-sequence impedance for three- and five limb power transformers with three (YY∆) and four windings (YYY∆) including a stabilizing winding. A stabilizing winding is a delta-connected winding which is not brought out; its purpose is to reduce and balance the zero-sequence impedance in adjacent windings. The value for the zero-sequence impedance can only be estimated since a direct measurement on the winding is not possible for this type of transformers. The resulting models are part of an algorithm where different transformer quantities are used as inputs to estimate the value of the zero-sequence impedance for a given transformer.

    The method used to obtain these models is based on an analysis of the correlation between the zero-sequence impedance and other known and calculated quantities where a linear regression based on the least-squares method produces an approximative trend line. This approximation is made more robust with a bisquare-weight algorithm where less weight is given to diverging data points. This process is carried out for all the transformers included in this study where general models are obtained. The process is then repeated for specific subgroups of transformers with the goal of deriving more accureate models for these subgroups. The subdivision criteria is based in coupling- and core type which includes an0- and yn0-couplings and three- and four limb cores respectively. The reliability of each model is analayized with respect to their goodness of fit, statistical relevance and the quality of the data used to develop the model. Only models with a substantial goodness of fit and which were based on a sufficiently large number of transformers to be considered statistically representative of the target group are included in the final algorithm. In general, all the data analyzed follows a normal distribution which indicates that there are few extreme values. Consequently, the data used in this study is condsidered to be appropriately distributed to determine its trend. The performance of the models for transformers with three windings was tested against the expected values for the zero-sequence impedance based on the approximation algorithm which is currently being used by Svk. The test results from some of the models match the expected values while oth deviations.

    MATLAB is used in this projetct as the development platform for all analyses

  • 32.
    Eiriksson, Eysteinn
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Distribution grid capacity for reactive power support2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The modern power system is changing at a rate faster than would have been expected20 years ago. More and more conventional power plants will be shut down in favour ofdistribution generation (DG). This is happening now with the trend of introducing renewableenergy sources (RES) to the power system.The grids were designed to transfer power from generating units connected to the highvoltage grids towards the end consumers connected to the low voltage grids. With changedpower mix, power flows in the system will change resulting in possible grid problems. Oneof the main problems is keeping the voltage within operational limits of the system. Whenthe generation exceeds the consumption in a distribution network, the power will flow fromthe low voltage network towards the high voltage network (reverse power flow) which willcause the voltage to rise in the low voltage network. Reactive power support from DG canbe a valuable resource to mitigate the problem. Reactive power is necessary to operatethe power system. The main source of reactive power is synchronous generators. If thissource is shut down, the reactive power must come from another source.This thesis investigates if DG could be used to support reactive power to the highvoltage transmission network to control the voltage. For this purpose, a distributionsystem located close toWorms, Germany will be studied. This distribution system consistsof two MV feeders with high penetration of DG, mostly photovoltaic (PV) but also windturbines (WT). Consumption and generation measurement data was provided by the localdistribution system operator (DSO). A few reactive power control methods are introducedand tested on this system. From the results, it is concluded that it is possible to providereactive power support from distribution networks and a voltage dependent reactive powercontrol can be used to this purpose.

  • 33.
    Elawa, AMR
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Översyn av skyddsanordning samt nollpunkt för fördelningsstationen Fs Myrängen2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This is a report of a Master’s thesis done in behalf of the local network

    in Stockholm, under Fortum Distribution AB. The thesis was to

    conduct a review of a distribution station named Fs Myrängen located in

    Täby. A model was created for the 11 kV network linked to the secondary

    side of Fs Myrängen. Based on this model and using symmetrical components,

    theoretical fault currents (short circuit and ground fault) could

    be calculated. The results of these fault currents are used to investigate

    and develop new settings for relay protection and ground equipment in

    the station. The results of the calculated fault currents were also used

    to investigate unwanted voltages that occurs for grounded parts due to

    earth faults. The value of these unwanted voltages was then compared

    to heavy current regulations developed by the Electrical Safety Authority

    in Sweden. Another element of the work was to create a rehabilitation

    plan for the structure on the 11 kV side of Fs Myrängen, the main goal

    regarding the rehabilitation plan was to investigate the advantages and

    disadvantages that exist at a possible transition to numerical protection

    relays. This was done by making a market overview of the different types

    of numerical protection relays and compare these with the existing analog

    protective device in Fs Myrängen.

    The study showed that protective relay settings should be revised according

    to the recommendations in the report, ground equipment should

    be replaced with a self-regulating type, transformers should be replaced

    due to age and capacity limitations. Regarding a switch to numerical

    protection relays the type REF615 from ABB was recommended, in that

    case the control board in the station should be replaced to a station computer.

    Furthermore should current transformers be replaced to recive a

    desired sensitivity regarding detection of ground faults. The report also

    showed that Fs Myrängen meets the regulations of unwanted voltages over

    grounded parts in distribution stations due to earth faults.

  • 34.
    Erbay, Ali
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Parameter Study of Ferro-Resonance with Harmonic Balance Method2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Ferro‐resonance is an electrical phenomenon which can cause damage to electrical equipments of power systems by its characteristic steady state over voltages and over currents. Configurations where ferro‐resonance is possible has more than one steady state operation. With time domain simulations, different dangerous steady state operations are hard to find due to the fact of dependancy of initial conditions and parameters of the system. Determination of risk of ferro‐resonance needs special studies involving frequency domain and Fourier series based harmonic balance method. Two different types of harmonic balance method are used; namely analytical and numerical method. In order to draw twoparameter continuous curves, harmonic balance with hyper‐sphere continuation method algorithm is created in MATHCAD environment. Work of two case studies in academic literature are extended by comparing different system parameter curves and calculating stability domain risk zones for fundamental ferro‐resonance, subharmonic‐1/2 and subharmonic ‐1/3 ferro‐resonance. Alstom’s test system is also investigated with approximations. Application of numerical harmonic balance method is more superior than analytical method since it is ease of use with thevenin equivalents rather than deriving system equation by hand and possibility to study subharmonic ferro‐resonance. Hypersphere continuation method worked well enough to turn limit points on parameter curves depending on considered Fourier components. Critical values for system parameters have been found for each type of ferro‐resonance allowing to analyse normal operation and ferroresonance operation regimes. Critical values of static damping resistor in the system can be calculated by harmonic balance method without using empirical formula. Damping resistor calculated by harmonic balance method showed difference than the one calculated by empirical formula. Fundamental and subharmonic ferro‐resonance solutions existence zones are co‐existant and sensitive to parameter changes therefore same attention should be given to subharmonic as in fundamental ferro‐resonance. For future studies, three‐phase models for harmonic balance method should be developed in order to study neutral isolated networks and a more customized method of solving non‐linear harmonic balance equations for faster computation can also be developed in MATLAB environment.

  • 35.
    FALEYE, OMOBOBOLA
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Modelling Demand Uncertainties in Generation-Transmission Expansion planning: A case study of the Nigerian Power System2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Nigerian power system is one plagued with incessant load shedding due to inadequate generation and transmission capacities. Currently, less than 40% of the population is connected to the national grid and less than 50% of the available installed capacity is actively used in meeting demand. A new wave of energy reforms is on-going in the nation. There are proposed generation and expansion plans. These reforms have only fully taken into consideration present demands and not future energy demands. This means that even with new plants and transmission lines being constructed; there may still be inefficient generation and transmission capacities due to demand increase. This thesis models the uncertain future demands in the integrated generation-transmission planning model. An optimal investment plan is found using the deterministic optimization model of integrated generationtransmission planning. A decision analysis method was initially used to study the introduction of uncertain demand into the deterministic model. Then, a two-stage stochastic model of the generation-transmission planning taking into account uncertainties in energy demand is developed using scenario-wise decomposition method. The demand was modelled as taking discrete values with certain probabilities. These models are mixed-integer linear programming problems. They are implemented in the GAMS platform and solved using the CPLEX solver. A stylized version of the Nigerian power system is developed and tested. A thorough analysis and comparison of results from the models were carried out using the developed version of the Nigerian transmission grid.

  • 36.
    Fazlagic, Berina
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Utilization and evaluation of the Swedish incentive scheme for the regulatory period 2016-20192017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The distribution system operators in Sweden act under monopoly, whichmeans that some of its operations and functions are regulated by thegovernment authority Swedish Energy Market Inspectorate (Ei). A centralpart of Ei's task is to determine the revenue cap for all distribution systemoperators. The revenue cap is among other determined by, capital costsand quality of distributing the power.In the 2016-2019 revenue framework driving forces, in the shape of incentives,have been introduced thus to achieve efficient utilization, whereas one ofthe incentives focuses on improving the load factor. This study indicateshow the load factor can be modulated, calculated, controlled in order togenerate a more efficient use of the power grid. This implies that Ei canuse the load factor as a control / reward factor, an incentive thus to inducedistribution system operators to strive for the European Union directiveregarding efficient utilization [1].The study has been based on studying following calculation models of theload factor:1) Annual average load factor, based on daily basis.2) Weighted average, a calculation model that weight days higher with ahigh load.3) Proposed calculation model of load factor that is based on several ratiosof load factor calculations. This model is based on the average sum of:daily load factor, weekly load factor, monthly load factor, seasonal loadfactor and yearly load factor.In addition to the first part of the study, a general optimization model hasbeen developed. The optimization model has been applied to visualizehow distribution system operators can adapt their business according toincentives to achieve optimal reward.The results from the first set of the study indicate significant differences inefficiency performance and financial outcomes, depending on whichmethod of the load factor is imposed in the incentive framework. Theproposed load factor strive and require greater power of action, thus toachieve a good utilization ratio.The result of the optimization problem demonstrates a basis for assessinghow a electricity grid company can adapt its operations, such as pricepricing for different periods of time, in recognition of incentive regulation.The results indicate that price is highly dependent on how price sensitivecustomers are in demand for electricity.

  • 37.
    Felix, Isbi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Dynamic analysis of the impact of grid connection of "La Higuera" hydropower plant to the transmission grid2006Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Studies regarding the development of a new hydropower plant exploiting the water resources offered by the upper Tinguiririca river, located about 150 km south-east of the capital Santiago in Chile, has been done by Pacific Hydro Ltd from Australia and Lahmeyer International from Germany. These studies have resulted in proposals to construct two Hydropower Stations, �La Higuera� and �Confluencia�. Both hydropower stations will have a total installed capacity of 300 MW.

    When setting up a new hydropower plant, it is important to foresee how the hydropower plant would affect the existing transmission grid in different situations during operation as well as how events in the grid may affect the La Higuera and/or Confluencia hydropower stations. In this report three kind of analysis are highlighted, which are static analysis, large signal stability and rotor angle stability. To perform these analyses a simulation tool named DigSilent is used. DigSilent is used to perform these analyses in a simulated network of the studied transmission system.

    These two hydropower stations as shown in the results will improve the existing transmission system by enhancing the stability margins in the presence of a fault. When performing the simulation of the existing transmission system with the newly installed hydropower plant we could see that it had a poor damping after a disturbance; this might be due to the large distance between production plants and the existing loads. This phenomenon can be alleviated if a power system stabilizer (PSS) is integrated in the hydropower plant.

    The final conclusion is that the integration of the two hydropower plants will improve the existing transmission system in Chile.

  • 38.
    Fernández Martínez, Alberto
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Grid planning with a large amount of small scale solar and wind power2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The total energy demand in the world is expected to increase in the future years due to thehigh development rate of developing countries. Access to energy enables development, butthe current global energy mix has to be modified if a sustainable growth is desired. Renewableenergy sources (RES) benefit from both a political and economic support from manygovernments and international entities. The growing installation of RES takes place both inlarge scale, as wind farms with sizes 10 – 1000 MW, and in small scale in homes or smallenterprises with sizes 100 W – 100 kW. Small scale wind power connected to the grid is rarenowadays except in the case of remote mini-grids. By contrast, small scale solar photovoltaic(PV) power is being more and more commonly installed, especially in the form of investorownedroof-installed units. Taking increasing small scale solar and wind power into accountin network planning is a challenge faced by the distribution system operator (DSO).The aim of this thesis is to present a guideline that assists DSOs when planning lowvoltage (LV) distribution networks (DN) with a large amount of small scale distributedgeneration (DG) on a short-term perspective. A review on integration issues of DG isperformed and over-voltage constraints are identified as the most relevant issue. Simple ruleshave already been designed for individual DG units, as the one presented in the AMKhandbookpublished by Svensk Energi; but these are not valid any more when consideringmore than one DG unit. The new proposed guideline employs the AMK-handbook as astarting point and develops it further by including the interaction between DG units. Theguideline is then applicable to scenarios with more than one DG unit. The maximum capacityof a new DG unit applying for a connection to a grid is calculated based on the location andcapacity of the already installed DG units, and without any reinforcement. The proposedguideline can be applied under no load and minimum load condition.Since this thesis is a collaboration project between KTH-Royal Institute of Technologyand Vattenfall R&D, two specific Swedish LV distribution networks owned by VattenfallEldistribution AB are studied. Scenarios with different penetration levels of DG, with valuesbetween 12% and 71%, and capacity of individual DG units below 43.5 kW are analyzed.Evaluation of the results shows that the proposed guideline leads to acceptable results. Thedevelopment of future simple guidelines is suggested to be based on the following twoaspects: absolute and relative location of the DG units; and a correct identification of the weakbus. Relative location reveals the interaction with other DG units within the DN. Moreover, itis stated that the use of the penetration level as a planning measure, based on the total DGcapacity, has a limited application.

  • 39.
    Fjällström, Emil
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Impact of Converter Modulation Strategies on the Losses in a Traction Motor2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With an increased demand on high-efficiency electrical machines in traction applications, better understanding

    in the losses induced by the converter is needed. The harmonic losses from the converter are

    non-negligible part of the total losses in an induction machine, and these harmonic losses have been

    studied here with a focus on iron, skin-effect and proximity losses. The main goal of the thesis is to

    advise how the modulation method can be changed to lower these time harmonic losses in an induction

    machine. A model of the induction machine was created in the FEM(Finite Element Method) software

    FLUX.

    The iron, the proximity and the skin-effect losses were simulated in the FLUX model with different

    modulation method to analyse the time harmonic losses due to respective phenomena.

    The modulation method at higher operation is square-wave modulation, this is due to that maximum

    fundamental voltage has been reached. At lower operation, pulse width modulation is used, and the

    switching frequency can be increased to lower the time harmonics losses in the motor.

    The iron losses simulated in FLUX show that the losses increase with frequency even if the motor

    enters flux weakening operation at higher frequencies.

    The proximity phenomena gives rise to a distinct increase of resistive losses in the conductor closest

    to the air gap in the stator winding.

    The skin-effect phenomena affects the losses at square-wave modulation of high frequencies mostly

    as the time harmonics are larger and of low order.

  • 40.
    Galland, Olga
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    The Short-Run Security-Constrained Economic Dispatch2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In liberalized electricity markets, the outputs of controllable units (both generatorsand demands) must be defined at regular time intervals ("dispatch intervals"). Nowadays,balancing services are procured and dispatched not in the most efficient waypartly due to long dispatch intervals. The dispatch interval in most European countriesis one hour. The shortest dispatch interval is five minutes and is used in theAustralian National Electricity Market (NEM). During the dispatch interval, demandand wind power capacity uctuates a lot. To keep the supply-demand balance in thesystem, some generators participate in frequency control. This action increases thesystem operation cost.By reducing the dispatch interval to short periods of time over which physical limitsof the power system are fully respected, balance services could be dispatched in amore efficient way. This improves the overall economic efficiency of the system.This work derives the mathematical model for short-run economic dispatch. For thismodeling, three stages are considered: (1) initial steady state in which the systemmight be exposed to a change, (2) the transition period which models the transitioncost after the change happened and before the system goes to another steady stateequilibrium, and finally (3) the final steady state equilibrium which models the systemcost when the change in the system has been handled by the exible generating units.These three stages are modeled in a single optimization problem. The developedoptimization problem is a linear programming problem. The developed formulationfor the short-run economic dispatch is modeled in GAMS platform. Two applicationsof the proposed model are discussed: (1) power system security, and (2) real-timebalancing market. In the first application, analysis of the optimal dispatch of nodaloperating reserves to provide sufficient exibility to survive a set of credible contingenciesis performed. In the second application, an algorithm for the dispatch ofbalancing services in the real-time balancing market is proposed . These two applicationsof the proposed short-run economic dispatch are tested on a simple six-busexample system and IEEE twenty-four-bus example system. The optimal dispatch isfound and conclusions are drawn. The numerical results of the proposed model showpromising results.

  • 41.
    GAO, XIANG
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Remedial Action Schemes Derived from Dynamic Security Assessment2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Electric power is becoming more and more important in the modern world. Since most electric power utilizations should be supplied by the power transmission and distribution system, the security of power system is paid more and more heed to nowadays. All over the world, there are some trends to introduce the deregulated power system into the power system operation, and to increase the stability of electric power supply. As a result, making accurate predictions for the power system operating conditions is an important task for the current power system research. The research mainly interests in checking if the operating conditions are acceptable after contingencies. Dynamic Security Assessment (DSA) is proposed and studied under such context. One tool to implement the DSA is to create the Stability Indices (SI) system. The SI system is used to indicate the operating conditions for the power system. This master thesis project aims to develop the appropriate Remedial Actions Scheme (RAS) by using the SI system. The RAS is used against different instabilities. Firstly, all indices of the SI system are summarized. The summarization is based on theoretical study on to-date DSA researches. The indices of the SI system are able to predict power system operating conditions. They are also able to release the stress of DSA computing, and to reduce misclassification and failed-alarm. The SI system is computed by quantities of state variables from the components of the power system. Secondly, the functionalities of different remedial actions are clarified. Then, those remedial actions are used to develop the RAS. The RAS is developed according to the evaluation by the SI system. Using the SI system, different remedial actions are tested and evaluated. The results of evaluation are used to develop and categorize different RASs against different instabilities. After that, the RASs are analyzed, and qualities of RASs are ranked by the SI. In this way, more suitable RAS against each type of instability is developed. The results show the process of analysis is both fast and accurate. All analysis and evaluations are implemented by simulation software of PSS TMNETOMAC. The thesis has been implemented between cooperation of Royal Institute of Technology (KTH) in Sweden and Energy Sector of Siemens AG in Germany.

  • 42.
    Garcia, Carlos Bernardo
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    Shielding of transformer stray fields in trains2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In construction of modern trains there are many requirements on the magneticstray fields from the train’s electrical components. These stray fields should not disturbneither other components in the train or components outside the train. Anotherimportant aspect is that the magnetic field exposure to the passengers shall be belowrequired levels.One component that creates stray field with high magnitudes is the maintransformer in the trains. In a recently manufactured Bombardier train, those fieldsreached unacceptable high values.In this Thesis a realistic 3D model of the transformer is created, in order toevaluate the effect that different shielding have on the stray fields. The first part isfocused on the transformer design, studying different materials that can be used for themagnetic core and the tank. In addition, the thickness of the tank is also studied.The second part evaluates the effect of different metallic shields on the leakageflux, in order to achieve a solution that reduces the stray field as much as possible usingthe least amount of shields.To build up the model and obtain the induction values, a FEM software has beenused.

  • 43.
    Gautam, Himanshu
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    The Impact of Customer Battery Storage on the Smart Grids and how Power Tariffs can increase Battery Storages’ penetration percentage2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The batterystoragewillplayanimportantroleinfuturesmartdistributiongrids.Atthesame time,thereshouldbeavailabilityofvaryingtariffstructures,fromwhichcustomerscan chooseaccordingtotheirrequirement.Thisresearchthesisfocusesonthestudyofimpact ofbatterystorageinthedistributiongridandhowpowertariffscanhelpincreasethebattery storage’spenetrationpercentage.The researchisdonetoassesstheimpactofbothhomebatteriesandEVsonthedistributiongrid, andhowmuchcantheyincreaseordecreasethedemandintheregion.Alsoapartofthesis isdedicatedtocreatenewpowertariffstructuresforStockholmregionofEllevio,andthenelectricity billsoftheconsumersarecomparedwithexistingtariffsandnewsuggestedtariffs.ForthethesisaresidentialareaofStockholmRoyalSeaport/NorraDjurgårdenstadenischosen.Ellevio iselectricitydistributionresponsibleforthearea.HomebatteriesofPowervaultU.KandTeslaPowerwall2arechosenandforEV,TeslaModelSwith60KWhbatterysizeisselected.One ofthemostinterestingfindingsisthatagroupof480customerswithhomebatterycanbring thepowerdemandduringpeakhoursdownbyupto11%,butontheotherhanda50%penetration ofEVintheareacanincreasedemandatcertainhoursbymorethan250%.Oneofother findingwasthatifcustomersshifttheirchargingpatternofEVbycoupleofhourstheycan increasethedemandinthegrid,emphasizingontheroleofcustomersinfuturedistributionsystems.SuggestedPowertariffsshowanincreaseinmonetaryamountsavedbycustomerifthey optforhomebatteries.Themostamountsavedbythecustomerisincaseofthestrictestpower tariffsuggested,i.e.Powertariffwithcriticaltimecomponentandtimeofusecomponent.This thesiswillbecomeafoundationforfuturestudyofimpactofbatteriesonalargerregionand impactofbatteriesownedbyDSOinthegrid.Italsoopensnewpathwaystostudyvaryingretail contractsforthecustomersandhowcombinationofvaryingretailcontractandpowertariffs canresultinbetterdemandflexibility.

  • 44.
    Gerlitz, Cecilia