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Studies Of Relay Protection Based On Wide-area Measurement Information And Related Issues

Posted on:2011-07-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y WangFull Text:PDF
GTID:1102360308454627Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
Smart grid is present situation of the development and changes in power systems, and it is considered as the most important technology innovation and development trend in power systems during 21st century. The final goal of smart grid is realizing the digitalization, informatization, automatization and alternation so that the smart gird would be established intelligently, strong, efficiently and reliably. As one of the most important investigated subjects for Smart grid, wide area protection system can resolve the unilateral and independent problem of the protection at present. Wide area protection system can also keep the large-scale power grid secure and steady, and it is indispensable. In this paper, wide-area protection of Smart grid and related issues has been discussed.A principle of preventing chain over-load trip based on wide-area information is proposed. Taking the important buses as units, the over-load current coefficient of each branch is calculated using relevant elements of the node impedance matrix in the normal operation conditions stored in the wide-area scheduling centre. The possibility of chain over-load trip caused by over-load branches is then estimated based on these coefficients, to help control centers take timely measures to prevent chain over-load trip and large-scale blackouts. The protection has simple principle, fast algorithm. It is also of great significance to the power grid safe and stable operation.A new method of wide-area protection against chain over-load trip (PACOLT) based on multi-Agent technology (MAT) is discussed in this paper. After expounding the Agent technology, and analyzing the structure of wide-area PACOLT based on MAT and the function and cooperation of all the inside modules, a new theory of wide-area PACOLT is proposed to prevent the Chain over-load trip and insure the reliability and continuity of power supply.In this paper, Wide area measurement system (WAMS) and Multi-sample-rate for Digital substation are studied. Because current (voltage) transformers and Phasor Measurement Unit (PMU) of Wide area measurement system in digital substation are different in type and sampling rates, it is necessary to convert them to the same rate. In this paper, sampling rate conversion in a rational factor is realized through cascade connection of extraction, interpolation and low-pass filter. A digital narrow band-pass filter algorithm based on full cycle Fourier algorithm is proposed. This algorithm can not only obtain the useful frequency component fast and effectively, but also realize the normalization of signals'sampling rate without distortion. The method Proposed is simple, fast, effective and can be used for security and stability of power system analysis, control and wide-area protection.Phase selection and fault location of Six-line transmission system based on Wide area measurement system are studied in the paper. This paper introduces the six sequence variables method to analysis the electrical signals gained from the end of transmission lines, and uses the same positive sequence (the parallel transmission lines system) or the opposite positive sequence (six phase transmission system) signal's long line equation to locate fault point. With the help of long line equation, the fault currents can be calculated form the location of fault and electrical signals gained from the end of transmission lines. The method proposed has high fault location accuracy and can select the right fault phase. The theory of the phase selection is clear and the logical of the protection is simple and reliable. It is also free from transition resistance and distributed capacitance current influence. This method can adjust the criterion of fault phase selection when operation mode is changed. It can provide effective phase selection logic for six-line transmission systems.
Keywords/Search Tags:Smart Grid, Wide-area Measurement Information, Protection against Chain Over-Load Trip (PACOLT), Multi-Agent Technology (MAT), Frequency Conversion, Six-line Transmission System, Fault Phase Selection and Location
PDF Full Text Request
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