The objective of this thesis work was to study the stability of a distribution network with several distributed generators (DGs) considering different types of regulators in the DGs and loading conditions. The distribution network under study, Øie – Kvinesdal, is a 57 km long radial feeder. It contains 8 distributed generators; seven synchronous and one induction generator. The largest generator has 10.3 MW rated power and the lowest has 0.25 MW rated power. The first and last generators are located 7.3 km and 45 km away from the 106/22 kV transformer respectively. Four of the synchronous generators are located on the same side branch.Four cases were studied with three different total active power production levels, two medium and one maximum production levels, and two different network loading conditions, high and low load.In each case, five different types of disturbances were created to analyse the dynamic response of the distribution network. The disturbances are synchronous generator disconnection, change in load, change in system voltage, short circuit fault, and disconnection of the 22 kV feeder from the HV network. Five different scenarios of synchronous generator disconnections were studied; disconnecting the largest four one by one and disconnecting the smallest three at the same time. Two different scenarios of load changes were studied. The first one is a step change in load either from high load to low load or from low load to high load depending on the initial loading condition of the network. The second type of change in load is disconnection of loads in one area which account to 66% of the total loads in the system. Change in system voltage was created by a 2.5 % step up on the swing bus voltage. The pre-disturbance linear analysis result showed that controllers connected to the smallest generators have strong relations with the least damped eigenvalues. The case with maximum generation and low loading had very low damped oscillations; as low as 6% damping ratios. Selecting appropriate regulator gain constants plays vital role in the distribution system’s small signal stability. There are some eigenvalues with imaginary part as high as 11 Hz. This is due to the low inertia of the distributed generators.The generators in all cases were able to regain synchronism after disturbances caused by disconnection of synchronous generators, change in load and system voltage. This is because the distribution network is connected to a strong high voltage network. But not all studied scenarios had terminal voltage and power factor within the allowed range in their post-disturbance steady state. Depending on settings of reactive power and over voltage relays, and how quickly a new set point is calculated for the excitation system controllers, a cascade of faults may occur. This could lead to instability. Relays were not included in this study.The critical clearing time for the case with maximum production and low load was the shortest because the distribution network had high voltage and the DGs were operating with their rated capacity in the pre-disturbance steady state. The distribution network was not able to reach new steady state, and be able to operate in island mode after disconnection of the feeder from the HV network with the turbine and governor models used.

Denne rapporten gjengir det arbeidet som er gjort i forbindelse med uttredelsen av muligheten for Skagerak Energi AS å bygge sitt egent PLS styrt kontrollanlegg til deres mange småkraftverk.Oppgaven gikk ut på å programmere en PLS, bygge et kontrollanlegg med komponenter ogsimulere et kraftverk for å sjekke om konfigurasjonen virket og om det var en reell mulighet for selskapet å bygge sitt eget kontrollanlegg. En Siemens PLS ble programmert til å være den overordnede styringsenheten i anlegget som tok seg av målinger, start- og stoppsekvensene, pumpestyringer og kommunikasjon med de resterende komponentene i anlegget. I tilegg ble en touch skjerm anskaffet og programmert til å vise diverse skjermbilder med relevant informasjon for kraftverksoperatøren. En aggregatregulator fra Hymatek AS tok seg av synkronisering, turbin- og spenningsregulering og et Siemens Siprotec vern ble benyttet.For å simulere et kraftverk ble det benyttet en aggregatsimulator som var innebygd iaggregatregulatoren til Hymatek AS og en Sverker ble benyttet til å teste vernet.

The introduction of large amounts of wind power into power systems will increase the production uncertainties due to unforeseen wind power production variations. This will have a significant impact on the required balance management quantities. The most suitable power source to balance fast production or consumption variations is hydropower because of its flexibility and low operational costs. This thesis addresses the problem of trading of electricity on the daily marketfrom a hydropower producer perspective in a system with large amounts of wind power. The overall aim is to present models that can be used in the trading decision process. This thesis describes models within three different areas:1. Modeling of the demand for balancing power by using deterministic andstochastic models. The stochastic models are based on stochastic differentialequations.2. Modeling of prices on the day-ahead and real-time markets using deterministic and stochastic models. The stochastic models are based on time series modeling.3. Short-term hydropower scheduling of trading decisions. These problems areformulated as stochastic optimization problems where the market prices arerandom variables. The first two can be used to simulate the impact of wind power on various market prices, while the third simulates how the hydropower producer responds to market prices. Thereby, the thesis presents the necessary models for short-term scheduling of hydropower for a future system with significant amounts of wind power. This thesis concludes that the proposed price models are sufficient to reflect the relevant price properties, and that the proposed short-term hydropower scheduling models can be used to simulate the actions taken by the hydropower producer in a system with significant amounts of wind power. This is also supported by the case studies in the appended publications. / QC 20100804

This paper is a report on master thesis project conducted in cooperation with SMARTMOTOR AS and NTNU. The research for electrical downhole drilling machine has developed for decades. Permanent Magnet is a new addition in this arena. SMARTMOTOR AS built a downhole drilling machine which is needed to compare with machines from other competitors of the market. This machine has 10% cogging torque over its rated torque. The reason of this cogging torque and possible solutions has been investigated throughout this project. And a new geometry and design of the rotor (with 10 poles) is suggested for the machine in this report. Measurement shows the newer design is less sensitivity to eccentricity. at nominal load and speed. Lastly, flux weakening and magnet working point of the machine also investigated. In this report it is concluded that out of 3 experimental designs, the design with less epoxy and more magnet offer better performance regarding voltage waveform and vibrations. It is superior in terms of torque per weight. The other designs however allow easier manufacturing, better efficiency and shorter length of machine. It It is therefore concluded that the last design with less epoxy can be a suitable alternative rotor design for the built up machine which can reduce the existing cogging torque upto 83.4%. The end part of the paper describes a template-style of a generic electromagnetic modeling tool for the analysis and optimization of Electrical Machines. Further accurate virtual prototypes can then be produced to help designers provide answers on the performance of specific machine designs rapidly. And further investigations to identify the design characteristics of the perfect machine. A two and three-dimensional FEA model for a generator and motor can be created in minutes, investigations to identify the design characteristics of the perfect machine. Optimization tool assists designers to find the 'best' solution automatically. The tool is structured to allow creation and analysis of customized geometries, including special proprietary features. A new Matlab-based script is developed in order to handle the optimization process of electrical machine which will be used in the finite element analysis. The script saves the designer’s valuable time. It is concluded that ‘fmincon-constrained nonlinear minimization’ method in new optimization tool of MATLAB is more accurate and less time consuming compared to the method for optimization. The report explains a modern design procedure which uses both analytical and numerical analysis. The numerical analysis uses finite element analysis that is performed in Comsol mostly.

Följande rapport beskriver ett projektarbete i att ersätta en automatisk spännings regulator (AVR) till en gammal ASEA dieselgeneratoranläggning. Generatorn är installerad på M/S Calmare Nyckel som tillhör Sjöfartshögskolan i Kalmar. Generatoranläggningen används enbart i utbildningssyfte. Den AVR som ska ersättas är en ASEA UTWH310. Det är ett väldigt gammal anläggning och vi uppskattar att den härstammar från 60-talet. Problemet med den gamla regulatorn är att när systemet har körts en stund så är det inte längre möjligt att reglera den reaktiva effekten. Vi blev tillfrågade att ersätta det gamla systemet, därför har vi inte gjort något försök att laga det. Regulatorn matar ström till en liten DC generator, mataren, som är ansluten till den större AC generatorn med remdrift. Mataren magnetiserar sedan rotorn i AC generatorn. För att få klarhet i hur systemet fungerade så gjorde vi några testkörningar. Vi tog reda på nödvändiga parametrar för att kunna ersätta den gamla anläggningen. Eftersom vi inte hade någon tidigare erfarenhet av den här typen av projekt, så hade vi lite problem att hitta en leverantör av den nya AVR utrustningen. Som tur var kom vi i kontakt med Subtron AB, ett litet företag från Enköping. De var mycket hjälpsamma, och de hade både kunskapen och utrustningen som vi behövde. Vi beslutade oss för att beställa Leroy-Somers R 448 AVR. Det är en enkel AVR men fullt kapabel att utföra det vi efterfrågar. Vi beställde också en del kringutrustning till installationen. Efter att ha testkört den nya utrustningen och kommit fram till att den fungerade utmärkt så utfördes installationen sedan på några dagar. / This following report describes a project in replacing the Automatic Voltage Regulator (AVR) in an old ASEA diesel generator system. The generator is installed on M/S Calmare Nyckel which belongs to Kalmar Maritime Academy. The Generator system is solely used for educational purposes. The AVR that is being replaced is an ASEA UTWH310. It is a very old system and we assume its from some where around 1960. The problem with the old AVR is that when the system has been running for a while there is no longer possible to control the reactive power. We were asked to replace the old system, so not much effort has been put on trying to repair it. The AVR feeds current to a small DC generator, feeder, witch is connected by a strap drive to the larger AC generator. The feeder then excites the rotor in the AC generator. To find out how the system actually worked we made some test runs. We measured necessary variables to be able to replace the old system. Because we had no formerly experience in this type of project, we had some troubles in finding a supplier of AVR equipment. Luckily we came in contact with a small company called Subtron AB from Enköping. They were very helpful and had both the equipments and the knowledge that we needed for our project. We decided to order Leroy-Somers R 448 AVR. It is a simple but fully capable AVR to preform what we asked for. We also ordered some auxiliary equipment for the installation. After a test run with the new equipment, we found out that it worked very well. The installation process was then made in a few days.

Hydroware Elevation Technology AB sells control and regulation equipment for hydraulic elevators. The company now wants to investigate the possibility of changing their present softstarters to frequency inverters to supply power to their pump engines. They also want to investigate the possibility of future use in so called ”intelligent” houses. The purpose of this report is to investigate these possibilities.

Fläkt Woods har ett fläktlab i Växjö där man utför kund och leveransprover av axiella fläktar. Befintlig anläggning är i dag bristfällig när det gäller driftsäkerhet och personsäkerhet. Även möjligheten att köra varvtalsreglerat är idag begränsad. Uppgiften är att projektera en ny anläggning omfattande en ny jordkabel, mellan- och lågspänningsställverk, transformatorer, kopplingsutrustningar och frekvensomriktare.

Harmonics are a well-known problem that has to be dealt with in the design of thegenerator. Internationally accepted standards limits the amount of harmonics allowedin the no-load voltage. These limits can be difficult to fulfill with integral slot winding,where the number of slots per pole and phase is an integer. The presence of thedamper winding often makes the problem with harmonics even worse and harmonicswith frequencies of order 6q±1 arise with significant amplitude. How the damperwinding is designed affect the content of harmonics in the no-load voltage and the aimwith these … has been to investigate in which extent design of the damper windingaffects the contents of harmonics.Simulations with the 2-D finite element method have showed that if the damper barsis centered in the pole shoe, the amplitude of the harmonics of order 6q±1dependsboth on the ratio between the stator slot pitch and damper bars slot pitch and if thedamper bars are connected between the poles or not.If the damper bars is displaced with ¼ stator slot pitch alternately, the amplitude ofthe harmonics of order 6q±1 is reduced and the influence of the ratio between thestator slot pitch and the damper bars slot pitch will vanish. To minimize the loss inthe damper bars the distance between the damper bars should then be equal thedistance between the stator slots.

Stability of a power system is vital for its reliable operation and maintaining system stability has been a big challenge for engineers over the years. One way of improving system stability is the use of power system stabiliser (PSS). Its main function is to add damping to the generator rotor oscillation by modulating the generator excitation so as to develop a component of electrical torque in phase with the rotor speed deviation. In Ghana, two power stations have their generators equipped with PSS but none of the PSS are activated. The main objective of this study is to assess how the stability of the power system of Ghana can be improved by activating the power system stabilizers (PSS) on the excitation system of some of the generating units. To effectively perform the study the following questions had to be answered.To what extent will the activation of the PSS on some generating units affect the overall system dynamic performance?Where in the power system should the PSS be activated?To what extend can the PSS reduces system oscillation? What improvement can be made to the power system to optimise the performance of the PSS?Data of Ghana and the interconnected systems were first collected, reviewed and all the systems were modelled using PSSE program. Steady state stability studies were then performed to identify the inadequacy in the system during steady state operations. Five base cases including peak and average load condition with and without contingency were used for this study. Dynamic stability studies were also carried out by selecting appropriate dynamic models for generators, exciters and governors that best fit the dynamic behaviour of the generating units in the PSSE program. Appropriate PSS models were selected for units equipped with PSS based on manufacturers’ recommendation. Series of dynamic simulations were carried out to identify the best location and parameter settings for the PSS. Small signal stability studies were also carried out to complement the results obtained from the transient studies using NEVA. There was however a defect in the NEVA program and full results could not be obtained.In conclusion, Ghana’s system is likely to experience voltage collapse during a transmission outage on some critical lines at peak period unless some loads are shed. This risk can be reduced by improving the power factor to 0.95 using more reactive power compensating devices (capacitor bank) at the local substation. Transient stability results also show that the best location for the PSS to effectively damped oscillation is Akosombo GS. Inter-area oscillations of 0.5Hz between Ghana and Ivory Coast systems, local-area oscillation of 0.8Hz between the Akosombo units and Aboadze units in Ghana, were effectively damped within 7sec with PSS at Akosombo GS. It is highly recommended that PSS at Akosombo generation station be activated since their application has a positive impact on the dynamic performance of Ghana’s system. Steady state stability be improved by correcting the power factor at the local stations and line relay settings reviewed to accommodate the present operating condition. It is also recommended that the PSS be coordinated effectively with the protection and control devices for optimal performanc

The work begins with a theoretical description of conductivity and the importance of this material property in the electrical power industry. The various theories describing high voltage conduction in highly insulating dielectric liquids are analysed to ascertain their propensity to explain the exponential rise in the conductivity of the insulating liquid at high fields.The work goes further to analyse the various methods and standards that are presently utilised in the measurement of conductivity of highly insulating oils. The short-comings of the present methods particularly the IEC 61620 and 60247 are identified. The physics behind the peculiar behaviour of the conductivity when stressed under high electric fields is described and analysed.Measurements carries out according to a standard, may not lead to useful results. Therefore, it is preferable to determine the conductivity under practical aspects and also to measure the different parameters on which the conductivity depends (1). A new method of carrying out conductivity measurements based on the use of triangular and sinusoidal input high voltage is used in this work.Conductivity analysis is carried out based on this method while time dependency, frequency dependency and field dependencies are studied.The results of the various results show a strong dependency of the resistance of the oil on the input electric field up to two powers of ten; when the electric field is varied from zero to 10 kV/mm for all frequencies. The frequency of input voltage has a minimum effect of the results of the conductivity up to 0.1 Hz; the only observable change is the increasing values of the capacitive current component of the measured total current.The time dependency of the resistance values shows a very remarkable variation of conductivity. There is an average of 3 times in the conductivity when the oil is stressed over a 24 hour period.Finally Comsol Multiphysics simulation is carried out to compare to the results of the experimental results obtained in the laboratory. The results of the current as well as the resistance values obtained using the comsol simulation bears great similarity to that of the laboratory experiments.