Research On Units Distribution In Self-Healing Decision Scheme Of Power Grid

With the rapid development of our country electric power system, power load increases sharply, more UHV ac and dc transmission line have been put into operation, the dynamic characteristics of power grid is becoming more and more complicated. According to recent years’ research on cascading failure in power system, results show that even strong system can not completely eliminate the possibility of failure and large-scale power failure always cause huge losses. Although power system failures are inevitable, powerful self-healing ability can help power grid defense fault in time as well as speed up the recovery process. Scientific and reasonable self-healing strategy build a fence for electricity network which improves immune ability of cascading failures. Thus it is of great importance and value to study distribution schemes of units that involve in self-healing decision schemes.Distribution of start-up units greatly affects power system restoration process. Studying and establishing a scientific and reasonable location scheme will not only help propel power system restoration process reducing the outage time effectively, but also inhibit the occurrence of cascading failure in the early stage minimizing outage scope and economic losses as much as possible. Therefore, from the perspective of graph theory, this paper firstly deduces two basic properties of location scheme: minimum branch inclusion and inheritance, and proves the inheritance by the method of reduction to absurdity. Then based on the inheritance property of scheme, recursive method is put forward. This method can quickly and accurately derive the optimal distribution scheme with fixed unit number. An economic benefit index of distribution scheme is established, with comprehensively consideration of economy and safety requirements to help researchers figure out suitable scheme from a series of optimal schemes. Due to the choice of both conventional black start units and thermal power unit with mature fast cutting load technology, this paper also establishes an evaluation index consisted by failure load factor and network impact factor to evaluate feasibility of transforming conventional unit into fast cut back unit under fault situation resulting in preventing cascading failures. Then six steps for deriving distribution scheme are pointed out. Finally the two different schemes are compared and by combining the two, an improving strategy of unit location has been put forward. A practical example is analyzed to verify the rationality and feasibility of the mentioned strategy. Results derived verify that the mentioned strategy can provide scientific and reliable decision advise for engineering practice and system planning.