Study Of Fast Search Algorithm For Flow Transferring Based On BFS And Over Load Emergency Control Strategy

In recent years, the frequent occurrence of blackouts in domestic and foreign countries have caused huge wastage to our social lives. In fact, most of these blackouts are caused by the cascading faults due to a single reload element, which may cause flow transferring. If it is controlled properly in the initial period of development, those blackouts can be avoided. Therefore, how to quickly and accurately find lines that influenced seriously by flow transferring to constitute a transmission section in order to avoid analysis and control of large-scale grid, and take emergency control measures to eliminate the overload when there is a possibility to cause a chain overload tripping accident, have become an important research topic in power system security control.This paper focus on transmission section fast search scheme research and transmission section chain overload preventive emergency control strategy research.First of all, this paper proposes a fast search algorithm for transmission section based on automotive relay. An automotive Relay model-based new algorithm is presented to quickly search the transmission section. Firstly, the power network can be turned into a topology, with nodes seen as stations and line impedance as path length. Secondly, according to certain rules, several cars of the same type take part in a relay between original and terminal station. Thirdly, as fuel consumption is proportional to the path length, cars could be sorted according to its remaining amount of gasoline, which means K shortest paths could be searched through backtracking. It is not necessary to derive large amounts of sub graphs, and the shortest paths could be got without repeatedly solving. The DC power flow transferring coefficient is introduced, and the coefficients of each branch in the paths searched are calculated. And the branch whose coefficient above certain value should join the transmission section, an accurate transmission section set without leaking lines is reached. Compared to the usage of a single path whose search range is too small, the automotive relay algorithm could avoid leaking lines and ensure integrity of transmission section. Finally an IEEE 30-bus system simulation is analyzed, demonstrating the effectiveness of the algorithm.Then, this paper proposes a fast search algorithm of transmission section for multi-branches removal event based on breadth first search. The concept of active power transferring coefficient is put forward, which of multi-line resection is reached via the calculation method of DC power flow. When the excision of many lines happens, by using the breadth priority search algorithm in graph theory, all the lines have been searched by level. Meanwhile their active power transferring coefficients are calculated, which could quickly search out the transmission section influenced greatly by power flow transferring, and solve the problem of leaking the line whose power flow increases reversely. Neither large-scale matrix operations nor the search of whole network topology is needed. Finally an IEEE 30-bus system simulation is analyzed, demonstrating the feasibility and effectiveness of the algorithm.Finally, this paper proposes an emergency control strategy for branches overload based on weighted sensitivity when many branches are overloaded, control demand is becoming more urgent with more serious overload, the concept of weighted sensitivity based on overload coefficient and comprehensive sensitivity is proposed. On this basis an optimal auxiliary control unit is introduced to obtain the geometric distance between each effective control unit and the optimal auxiliary control unit, a shorter distance means a stronger comprehensive ability to eliminate many branches. Take the smallest distance as the optimal control unit, and then determine controlled variable considering generator and load adjustment ranges and normal branch flow redundancy. And real time load shedding control is implemented for the next round of control until elimination of all overload situations.The IEEE 30-bus system is used as an example to test and analysis both the methods in the paper. The application outcome shows that the three algorithms are able to achieve the desire result. The methods proposed in this paper can provide some effective research thought for avoiding black outs and some reference for the safety analysis and control of the power system.