Preliminary Study Of Generalized Short-circuit Current Limitation In Power Grid

With the expansion of power system and the growing level of relational degree, short-circuit current is increased year by year. At the same time, another noticeable question is that the non-equilibrium distributing situation of short-circuit capacity in the whole network has become increasingly evident. This phenomenon threatens the operational safety of power grid and the switch breaking capacity. Therefore, the short-circuit capacity of the power network must be decided in the middle way between the running quality and the breaking capacity of the switches.The generalized short-circuit current limitation approach is proposed in this thesis. The purpose of this thesis is to explore the reasonable distribution of short-circuit capacity by changes of the operating modes, in order to reduce the differences of the short-circuit capacity between the various nodes. By this solution, the nodes which short-circuit capacity is lower can be enhanced the anti-disturbance capacity. Moreover, it can lower the short-circuit capacity of some nodes to achieve the purpose of limiting short-circuit current. Regarding the short-circuit current as a clue, this thesis organically considers the relationship between the normal operation mode of the power system and the limitations of the short-circuit current, and carries out some research works as follows:The analysis of the relationship between the possible operating modes and the short-circuit capacity will be given first. There are many operating modes you can choose to run in the power system. Different operating mode corresponds to a different distribution of short-circuit capacity of each node. So, it is essential to describe the possible operating mode in order to study the distribution of short-circuit capacity. Combining the physical meaning of the short-circuit capacity of and variability of the power system operating mode, this thesis describe the definition of the possible operating mode in detail, and propose the effective switch sets as the decision-making space of the operating mode. On this basis, the functional relationship between the operating modes and short-circuit capacity is established. It sets the stage for furthering the research of the short-circuit capacity. The changes in operating modes base on the adjustable switches in the power plants and substations in this thesis. However, the number of adjustable switches is huge for a complex power grid. To simplify the computational effort, this thesis processes all adjustable switches and describes the effective switch sets which can decide the operation modes. Then the model of the topological analysis is built. The meaning of the topological analysis here is to find the connectivity of nodes by the adjustable switches state and provide the actual network structure for flow calculation and short-circuit calculation.On the basis of the above two-step, this thesis expand approaching the distribution of short-circuit capacity in the power grid. With the change of power structure, the thesis proposes an optimal method which can make a compromise decision for short-circuit capacity distribution. In this method, the target is the balance of short-circuit capacity in power grid, and seeks the compromise optimal program between short-circuit current limitation and the operation mode, in order to achieve the generalized short-circuit current limitation. At last, the validity and actual value of the thesis is proved by two examples.All in all, as the development of network scale and the diversity, the generalized limitation is useful to the operation and the expansion planning in power grid. The long-term and sustained research has important guiding effects for the investment and operational safety. This thesis is the preliminary study, further study is still continuing.