Research On New Technologies Of Power System Intelligent Protection

A salient characteristic of the recent developments in protective relaying is the use of intelligence and information technologies in protection devices. It was a great leap that traditional analog protective relays were replaced by microcomputer-based protection relays. The powerful computation and analysis capabilities of microcomputer-based relays make it possible to take full advantage of Digital Signal Processing, Artificial intelligence and many other interdisciplinary technologies. As such, not only can the protection functions be optimized, but also the protection principles and performances can be improved significantly. In this paper, the power swing issue in distance protection and the inrush current issue in transformer protection are discussed. The two problems are essentially identification problems of complex states, and have not been solved successfully in conventional relays. Fuzzy set theory and wavelet analysis are used in this thesis to identify the states according to their external characteristics and internal rules. Advancement in communication technology is one of the prime movers of protection principles. With the informationization process of microcomputer- based protection relaying, the integration of power system protection and control becomes more and more noticeable, especially in communication based distribution system protection. This paper covers a network-based distribution line carrier communication system, which offers a solution to integrated distribution integrated automation based on distribution system protection with distribution line carrier communication. The main contents of this paper are: I Power swing issue is a focus of distance relay research. In this thesis a new principle is provided to identify three-phase faults under power swing conditions, which is based on fuzzy set theory. The states of power swing and three-phase fault have many common characteristics. Based on the overall state changes of electrical waveform, the new principle distinguishes the voltage changes at swing center before and after three-phase fault under power swing conditions. The fuzzy feature of the identification process offers a good time response and makes the method more robust. The principle can be also applied in the identification of phase-phase faults under swing conditions. 2 Based on the concepts of synthetic space vectors, synthetic negative-sequence vector (SNSV) concepts and a highly accurate algorithm are provided in this thesis. SNSV is very useful in the identification of non-symmetrical faults. However, due to the high sensitivity of the current negative- sequence algorithms to system frequency, a large proportion of non-balance output can not be avoided under power swing conditions, which greatly affects the sensitivity of negative-sequence component. By contrast, the integrated negative-sequence component is not influenced by system frequency and has a high accuracy. Thus, combining synthetic negative-sequence component and zero-sequence component, earth faults during power swings can be identified reliably. 3 A new fault-phase identification method is offered for earth faults under power swing conditions. For distance protection, fault-phase identification is of great importance in the clearance of non- symmetrical faults under power swing conditions. In this paper, based on the comparison of three phase Isin q?before and after non-symmetrical faults under swing conditions, fault-phase identification can be realized. 4 Inrush current identification is a key problem in transformer protection...