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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Control and protection of high voltage direct current systems

Hingorani, N. G. January 1961 (has links)
No description available.
22

Revisión de equipos y procedimientos de medición de campos eléctricos en líneas HVDC

Duarte Conte, Carlos January 2014 (has links)
Ingeniero Civil Eléctrico / La pronta llegada de los eventuales proyectos energéticos que se planifican en la XI región de Aysén ha planteado el desafío de transportar grandes bloques de potencia a través de largas distancias, hacia los centros de consumo que se concentran en el SIC. La tecnología que permite posibilitar esto de manera eficiente es la transmisión en corriente continua en alto voltaje, conocida como HVDC (High Voltage Direct Current). La tecnología HVDC se puede considerar como una tecnología madura. Sin embargo, en nuestro país es un tema relativamente nuevo que se debe abordar para entender el funcionamiento del enlace y los problemas asociados. Esta memoria está divida en tres partes principales, la primera, relacionada con la física del efecto corona, clasificación y características; por otra parte, la segunda, tiene como objetivo estudiar en forma teórica algunos de los mecanismos de medición de campo eléctrico generados por líneas de transmisión en corriente continua, los cuales requieren distintos tipos de consideraciones. En la tercera parte, se incluye una comparación de varios medidores y su puesta a prueba en las líneas HVDC bajo diferentes condiciones de carga y/o campos estáticos. Utilizando un modelo afín para evaluar el comportamiento de los medidores bajo distintos escenarios, se determina cuáles de ellos presentan mejor estabilidad al realizar una o varias mediciones. Esto será muy importante a la hora de implementar o importar un equipo de medición de campo eléctrico utilizado en líneas HVDC.
23

A robust wide area measurement based controller for networks with embedded HVDC links

Agnihotri, Prashant 12 August 2016 (has links)
The advent of Wide-Area measurement Systems has spurred interest in the use of non-local feedback signals for power swing damping control. Although damping can be improved through generator excitation systems, dc links and other grid connected power electronic converters, the full potential of wide-area measurements can be realized by coordinating the strategies used for multiple controllable devices in a grid. These strategies also need to be robust to partial or complete loss of communication, changes in operating points, topology and equipment outages, improve damping of all the controllable swing modes, and have adequate stability margins to avoid destabilization of untargeted modes. This thesis investigates a control strategy for multi-infeed and multi-terminal (also referred to as multiple embedded dc links in this thesis) dc links using local frequency difference signals as well as the frequency difference signals obtained from other dc links. This strategy combines the advantages of the local frequency difference signal with the additional degrees of freedom provided by the use of non-local frequency difference signals, to achieve targeted and enhanced swing mode damping for the poorly damped modes. Since the strategy uses only a limited set of non-local signals, the signals may be directly communicated to the dc links without having to be centrally collated with other system-wide measurements. The key aspect of the proposed strategy is the use of a symmetric positive definite (spd) gain matrix. This results in enhanced damping for all controllable swing modes. Furthermore, loss of communication between the dc links does not destroy the symmetric positive definiteness and the gain elements can be tuned to selectively enhance damping of poorly damped modes. Eigenvalue sensitivity analysis and case studies on a 3 machine 9 bus and 16 machine 68 bus system with multiple HVDC links are presented to demonstrate the key attributes and the effectiveness of this strategy. / October 2016
24

LCC Bipole with one station earthed via a large capacitor : Theory and simulations

Jernberg, Johan January 2016 (has links)
If one of the two poles will trip for some reasons in a regular bipolar HVDC transmission without a return conductor, it is necessary to block the other pole temporarily during the transition to a monopolar operation with metallic return, this procedure will take 1-2 seconds and will affect the connected AC networks by extra disturbances. The object of this survey has been to answer the question if it is possible to have a balanced bipolar transmission without a return conductor and during a trip of one pole control it as an HVDC transmission with series connected converters by adding the by-pass switches and the logic for a series connected HVDC converter system which means that a shutdown of the transferred power during the transition phases is not necessary. The survey has been performed with the software PSCAD where an already existing series connected converter circuit had been modified to a bipolar system and the control logic for the transition phases has been created. There were some problems with various control signals between the software HiDraw and PSCAD, this was solved by different methods and the result shows that it is possible to have a transition between bipolar operation and monopolar operation with metallic return without the need to totally shut down the power transfer completely. But this requires a large capacitor.
25

The protection of transmission networks containing AC and DC circuits

Wang, Hualei January 2015 (has links)
In 14th August 2003, the Northeast USA suffered its worst power outage event in history. The power disturbance spreading through the system caused mal-trips of the distance relay remote back-up protections, which indeed contributed to the power outage cascading a wide area. The power outage in the Northeast USA was constrained by the presence of HVDC interconnections between the HVAC networks in Ontario and New York. The system collapse did not progress beyond the HVDC interconnection interface with Quebec. The HVDC link can regulate the voltage and current therefore impacts on the performance of the protection and system stability. The distance relay mal-operations were one of the main cause of the Northeast USA blackout as well as the other recent major large area blackouts which were pointed out by the previous papers. This thesis is focus on investigate how HVDC interconnections contribute to maintaining the power system stability. The research work investigated the performance of a distance relay to faults and disturbance on networks containing HVDC interconnection. The research work was carried out by modelling and testing a classic signal processing distance relay in a simple AC network which was based on Kunder’s two areas system using MATLAB/SIMULINK at first. Then the modeled distance relay’s performance was investigated by combining the distance relay and a simple HVDC link based on the Kunder’s two areas system. The research work firstly combined the signal processing distance relay and the HVDC link together to investigate the distance relay’s performance when the protected feeder containing DC link. The distance relay’s performance was investigated when the protected feeders containing HVDC link under fault conditions and power swing conditions. For comparison, a similar power system without HVDC link was also simulated.
26

Stability and redundancy studies on the electrical grid on Gotland with respect to 500 MW of new wind power and a VSC HVDC link to the mainland

Larsson, Martin January 2013 (has links)
The electric grid of Gotland is connected to the mainland via a 90 km HVDC Classic bipole of 2 * 130 MW. The HVDC link balances the load and production on the island to maintain the frequency within limits, the load varies between 50 and 180 MW throughout the year. The power production on the island comes mainly from wind power. Today, the installed power is about 170 MW but the wind power production will be further exploited and the plan is to add another 500 MW of wind power capacity to the existing plants. These plants will be connected to a new 130 kV transmission grid which will have a connection to the existing 70 kV grid at a new substation called Stenkumla. Along with the increased wind power production on the island comes the need of increased transmission capacity to the mainland. A VSC HVDC link of 500 MW is planned for this purpose and it will be connected to Stenkumla. As of today, it is not certain whether the two grids will be connected or not. Having connected grids is in the interest of the grid owner Gotlands Energi AB, GEAB since they then could utilize the technology of the new link and thereby ensure stableoperation during faults that today would lead to black out. In this thesis the feasibility of having connected grids was investigated and the study was divided into three main parts. •Reactive power and voltage profiles •Short circuit study •Converter trip study This study shows that under the assumptions made regarding production grid layout and proportion of WTG types there will be no need for adding reactive power compensation equipment. That is provided that demands are set on wind power plant contractors to have their equipment contributing with reactive power compensation, even during no load. A trip of the SvK VSC HVDC converter during full power production causes the most severe stress to the system. The major problem proved to be surviving the first 100 ms after converter trip without loosing angular stability and the most important measure to improve the stability was active power reduction of the wind turbines. The overall conclusion is that it is feasible to have connected grids during normal operation but demands has to be put on wind power plant contractors.
27

Travelling Wave Based DC Line Fault Location in VSC HVDC Systems

Karasin Pathirannahalage, Amila Nuwan Pathirana 04 January 2013 (has links)
Travelling wave based fault location techniques work well for line commutated converter (LCC) based high voltage direct current (HVDC) transmission lines, but the large capacitors at the DC line terminals makes application of the same techniques for voltage source converter (VSC) based HVDC schemes challenging. A range of possible signals for detecting the fault generated travelling wave arrival times was investigated. Considering a typical VSC HVDC system topology and based on the study, an efficient detection scheme was proposed. In this scheme, the rate of change of the current through the surge capacitor located at each line terminal is measured by using a Rogowski coil and compared with a threshold to detect the wave fronts. Simulation studies in PSCAD showed that fault location accuracy of ±100 m is achievable for a 300 km long cable and 1000 km long overhead line. Experimental measurements in a practical HVDC converter station confirmed the viability of the proposed measurement scheme.
28

Small-signal Dynamic Stability Enhancement Of A DC-segmented AC Power System

Pirooz Azad, Sahar 21 August 2014 (has links)
This thesis proposes a control strategy for small-signal dynamic stability enhancement of a DC-segmented AC power system. This control strategy provides four control schemes based on HVDC supplementary control or modification of the operational condition of the HVDC control system to improve the system stability by (i) damping the oscillations within a segment using supplementary current control of a line-commutated HVDC link, based on the model predictive control (MPC) method (control scheme 1), (ii) minimizing the propagation of dynamics among the segments based on a coordinated linear quadratic Gaussian (LQG)-based supplementary control (control scheme 2), (iii) selectively distributing the oscillations among the segments based on a coordinated LQG-based supplementary control (control scheme 3) and (iv) changing the set-points of the HVDC control system in the direction determined based on the sensitivities of the Hopf stability margin to the HVDC links set-points (control scheme 4). Depending on the system characteristics, one or more of the proposed control schemes may be effective for mitigating the system oscillations. Study results show that (i) control scheme 1 leads to damped low-frequency oscillations and provides fast recovery times after faults, (ii) under control scheme 2, each segment in a DC-segmented system can experience major disturbances without causing adjacent segments to experience the disturbances with the same degree of severity, (iii) control scheme 3 enables the controlled propagation of the oscillations among segments and damps out the oscillatory dynamics in the faulted segment, and (iv) control scheme 4 improves the stability margin for Hopf bifurcations caused by various events. Since power system software tools exhibit limitations for advanced control design, this thesis also presents a methodology based on MATLAB/Simulink software to (i) systematically construct the nonlinear differential-algebraic model of an AC-DC system, and (ii) automatically extract a linearized state space model of the system for the design of the proposed control schemes. The nonlinear model also serves as a platform for the time-domain simulation of power system dynamics. The accuracy of the MATLAB/Simulink-based AC-DC power system model and time-domain simulation platform is validated by comparison against PSS/E.
29

Travelling Wave Based DC Line Fault Location in VSC HVDC Systems

Karasin Pathirannahalage, Amila Nuwan Pathirana 04 January 2013 (has links)
Travelling wave based fault location techniques work well for line commutated converter (LCC) based high voltage direct current (HVDC) transmission lines, but the large capacitors at the DC line terminals makes application of the same techniques for voltage source converter (VSC) based HVDC schemes challenging. A range of possible signals for detecting the fault generated travelling wave arrival times was investigated. Considering a typical VSC HVDC system topology and based on the study, an efficient detection scheme was proposed. In this scheme, the rate of change of the current through the surge capacitor located at each line terminal is measured by using a Rogowski coil and compared with a threshold to detect the wave fronts. Simulation studies in PSCAD showed that fault location accuracy of ±100 m is achievable for a 300 km long cable and 1000 km long overhead line. Experimental measurements in a practical HVDC converter station confirmed the viability of the proposed measurement scheme.
30

Automated Testing of HVDC Control & Protection Systems : A study on Automated Regression Testing

Halvarsson, Hampus January 2018 (has links)
Testing is an important activity when developing a system. Testing requires resources in terms of time, labour and money. By correctly automating the tests, the development time may either be shortened or there will be a possibility to run more tests. ABB in Ludvika has developed MACH, a control & protection system for HVDC (high power electrical transmission over long distances) applications. During development of the control & protection system for each HVDC project, which are all unique, the system is today tested manually, which takes considerable time.This thesis project studies the possibility of automating parts of the MACH system tests, by investigating current testing procedures, the control & protection system itself, and how a test tool may interact with the system. Using this information a test framework, aimed towards test automation, was created, and a simple test execution tool was developed. A new test case, a combination of multiple smaller test cases, ranon the system using the test execution tool.The outcome proves the proof of concept of automating parts of the system tests.The economics and the scope of the automated testing however, is dependent on how automation is implemented.

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