142 research outputs found
Statisk Analys av Elsystem
No full textI detta kompendium behandlas modeller och beräkningsmetoder för statiska förhållanden i elsystem. I kapitel 2 beskrivs hur elkraftsystemet är uppbyggt och kapitel 3 behandlar den grund-läggande växelströmsteorin. Modeller för kraftledningar och transformatorer utvecklas i kapitel 4 och i kapitel 5 beskrivs några viktiga teorem som används vid analys av trefaskretsar. I kapitel 6 och 7 används bl a dessa till att utföra beräkningar i elsystem under symmetriska förhållanden. Kapitel 5-7 bygger på att man kan beskriva laster i elsystemet såsom impedanser. Detta leder till linjära förhållanden vilket ger relativt enkla lösningsmetoder. I vissa situationer är det mer relevant att beskriva elsystemets laster med effekter. Hur elsystemet analyseras under dessa förhållanden beskrivs närmare i kapitel 8. I kapitel 9 ges en översyn till möjligheterna att utnyttja linjära transformationer för att förenkla beräkningar i elsystem. I kapitel 10-13 beskrivs grunderna för analys under osym-metriska förhållanden. Vid osymmetrisk analys utnyttjas normalt symmetriska komponenter vilka beskrivs utförligt i kapitel 10. Vid osymmetriska förhållanden måste ledningar, kablaroch transformatorer få en noggrannare beskrivning vilket behandlas i kapitel 11-12. I kapitel 13 beskrivs hur ett osymmetriskt trefasnät med impedanslaster kan analyseras. Kapitel 3-13 förutsätter att man i elsystemet har en konstant frekvens och linjära komponenter dvs sinusformade spänningar ger upphov till sinusformade strömmar. Med olinjärakomponenter, såsom t ex kraftelektronik, i systemet uppstår icke rent sinusformade strömmar och spänningar. Vilka effekter det kan få på ett elsystem beskrivs översiktligt i kapitel 14.QC 20170227</p
Improving PV Hosting Capacity of Distribution Grids Considering Dynamic Voltage Characteristic
No full textA probabilistic distance to the power system secure operation boundary
No full textEstimation of power system operation boundaries is an important issue in power system engineering. To make an adequate approximation of the operation boundary, not only the geometric properties of the boundary have to be taken under consideration but also the stochastic properties of the future injected power. In this paper two different distance functions on the power system operation boundary are suggested. The methods used to find the distance functions assumes that the future injected power can be modeled by a diffusion process. The proposed distance functions can be used when an approximation such as a Taylor's expansion of the power system operation boundary is needed. It is then suggested to use the point on the operation boundary that minimizes one of the proposed distance functions, as the basis for the approximation. Another possible application of the distance functions is when wanting to control power system equipment in order to increase stability margins.</p
Railway Power Supply Investment Decisions Considering the Voltage Drops - Assuming the Future Traffic to Be Known
No full textTransports on rail are increasing and major railway infrastructure investments are expected. An important part of this infrastructure is the railway power supply system. The future railway power demands are naturally not known for certain. The more distant the uncertain future is, the greater the number of scenarios that have to be considered. Large numbers of scenarios make time demanding simulations unattractive. Therefore a fast approximator that uses aggregated railway power supply system information has been developed. In particular the approximator studies the impacts of voltage drops on the traffic flow. The weaker the power system and the heavier the traffic, the greater the voltage drops. And the greater the voltage drops, the more limited the maximal attainable tractive force on the locomotives. That approximator is in this paper used as a constraint in the embryo of a railway power supply system investment planning program, where investment decisions are assumed to be realized immediately, and there is no preexisting power supply system to consider. The traffic forecasts are in this first approach assumed to be perfect. This stepwise creation of the planning program makes evaluating it easier. The basic investment planning model presented here constitutes the foundation for further improvements.</p
The potential of distribution grid as an alternative source for reactive power control in transmission grid
No full textImpacts of Frequency Containment Reserve on the Optimal Coordinated Hydropower Scheduling in Three-Settlement Markets
No full textThis paper investigates the coordinated scheduling of hydropower plants in a river participating in a day-ahead, regulation and reserve markets. The gains in participating in the multiple sequential electricity markets are formulated through the linear programming. In the reserve market, the possibility of proposing an unsymmetrical frequency containment reserve (FCR) is considered for two scenarios in the winter and summer. Furthermore, the impacts of active time of regulation bids are investigated. The results show a moderate revenue increase by participating in the reserve market. Also, it states that providing the unsymmetrical FCR market will even increase revenue as an incentive for the owners to participate.</p
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