The Set Of Power System Operation Condition & Its Application To Relay Setting & Coordination

In order to improve the rate of protective relays correct operation in all kinds of operation conditions, and solve the problem that the set of operation condition isn't perfect, this paper analyzes how to establish the set of operation condition and its application to the relay setting and coordination.In relay setting and coordination, the basic requirements to select the operation condition are mainly as follows, the first is to full-scale selection which ensures the protective relays operate correctly; the second is the calculation efficiency. The formerly methods always can't consider the two requirements at the same time. One kind of methods mainly considers the full-scale selection, but expends large quantity calculation. The other kind of method improves the calculation efficiency, but cannot ensure the full-scale selection.In view of the two basic requirements of the operation condition selection, this paper first search simple loops on the graph theory to determine the scope in which the most unfavourable operation condition probably arises. Then depending on the electric current distribution, the key branches are found and the set of operation condition are established. When use the depth-first search/backtracking technique to search the simple loops, the new conception of the set of connection is introduced, which reduce the search quantities and make the search process clearly. In order to calculate the electric current distribution, the fictitious branch is introduced and the unified model to calculate electric current is established. Based on the electric network theory the formulae to calculate the branch current are deduced. When a unit of current is injected to the fictitious branch, the network branches'current can be conveniently got on the formulae. This method avoids forming the matrix of impedance when the network doesn't include the generator branches.Used the approach of this paper, a computer-aided software to built the set of power system operation condition is completed using VB6.0 in the Windows. This soft ware has been used in LiaoYan power system and testified that the method presented in this paper is correct and practicable.