abstract: Until late 1970’s the primary focus in power system modeling has been largely directed towards power system generation and transmission. Over the years, the importance of load modeling grew and having an accurate representation of load played an important role in the planning and operation studies. With an emphasis on tackling the topic of load modeling, this thesis presents the following intermediary steps in developing accurate load models: 1. Synthesis of a three-phase standard feeder and load model using the measured voltages and currents, for events such as faults and feeder pickup cases, obtained at the head of the feeder. 2. Investigated the impact of the synthesized standard feeder and load model on the sub-transmission system for a feeder pick-up case. In the first phase of this project, a standard feeder and load model had been synthesized by capturing the current transients when three-phase voltage measurements (obtained from a local electric utility) are played-in as input to the synthesized model. The comparison between the measured currents and the simulated currents obtained using an electromagnetic transient analysis software (PSCAD) are made at the head of the designed feeder. The synthesized load model has a load composition which includes impedance loads, single-phase induction motor loads and three-phase induction motor loads. The parameters of the motor models are adjusted to obtain a good correspondence between measured three-phase currents and simulated current responses at the head of the feeder when subjected to events under which measurements were obtained on the feeder. These events include faults which occurred upstream of the feeder at a higher voltage level and a feeder pickup event that occurred downstream from the head of the feeder. Two different load compositions have been obtained for this feeder and load model depending on the types of load present in the surrounding area (residential or industrial/commercial). The second phase of this project examines the impact of the feeder pick-up event on the 69 kV sub-transmission system using the obtained standard feeder and load model. Using the 69 kV network data obtained from a local utility, a sub-transmission network has been built in PSCAD. The main difference between the first and second phase of this project is that no measurements are played-in to the model in the latter case. Instead, the feeder pick-up event at a particular substation is simulated using the reduced equivalent of the 69 kV sub-transmission circuit together with the synthesized three-phase models of the feeder and the loads obtained in the first phase of the project. Using this analysis, it is observed that a good correspondence between the PSCAD simulated values of both three-phase voltages and currents with their corresponding measured responses at the substation is achieved. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2018

In order to meet the increasing demand ofenergy in today’s society while at the same time minimizing theenvironmental impact, renewable energy sources will be requiredto be integrated into the existing energy mix. Technologicaladvances in high voltage direct current (HVDC) grids playa crucial role in making this possible. Therefore the purposeof this project has been to validate the properties of basiccontrol strategies in terms of how they respond to four differentsimulation cases. All simulations have been conducted on asimplified version of the CIGR ́E B4 test grid, consisting offour monopolar HVDC converters. After analyzing the resultsobtained from each control strategy it became evident thatprovided if the benefits of the redundancy introduced by amulti-terminal grid are to be fully utilized, a distributed voltagecontrol should be used. Moreover, after substituting one ofthe four internal controllers with an external one, it becameclear that simply deciding the droop constants based on resultsfrom the simulation model wouldn’t be sufficient for real worldapplications. / För att möta det ökande energibehovet i dagens samhälle, samtidigt som energiproduktionens miljöpåverkan ska minimeras, krävs det att förnyelsebara energikällor integreras i den existerande energimixen. Tekniska framsteg inom högspända likströmsnät (HVDC) spelar en avgörande roll i att göra detta möjligt. Därför har syftet med detta projekt varit att validera egenskaperna hos grundläggande kontrollstrategier efter hur dem reagerar på fyra olika simuleringsfall. Alla simuleringar har genomförts på en förenklad version av CIGRE´ B4 testsystem, bestående av fyra monopolära HVDC omriktare. Efter att analyserat de erhållna resultaten från varje kontrollstrategi blev det uppenbart att om fördelarna med multiterminala elnät skulle uppnås, bör en distribuerad spänningskontroll användas. Dessutom, efter att ha bytt ut en av dem fyra interna kontrollerna med en extern, visade det sig att endast bestämma droppkonstanterna baserat på resultat från simuleringsmodellen inte är tillräckligt för verkliga applikationer. / Kandidatexjobb i elektroteknik 2020, KTH, Stockholm