Key Protection Assessment And Its Application In Optimization Of Setting Calculation Starting Point

The basic task of relay protection setting calculation in power system is to provide a reasonable setting value for the protection relays.So that protection relays can coordinate with each other in the event of malfunction and accurately remove the fault to avoid the accident range expanding and reduce the loss of fault.The correct setting calculation is an important guarantee for the security and stability of modern complex power grids.Its research has important theoretical and practical significance for improving the safe operation level of power grids.With the development of modern transregional and even transnational power grids,more and more loop networks appear in the system.It makes the significant step of setting calculation very important,which is to ensure the setting calculation starting point.This paper focus on the optimization of setting calculation starting point in loop network.The research contents include finding the minimum break point set by using optimization method and dimensionality reduction principle of protection dependency,evaluating the relay protection importance in power system,selecting minimum break protection dependency set by using optimization method and relay protection importance.The specific research contents and achievement are as follows:A dimension reduction principle of protection dependency based on protection function dependency list is proposed,and the minimum breakpoint set is obtained by combining with improved biogeography optimization algorithm.The principle can simplify the protection dependency and reduce the computational cost when dealing with complex grid.The improved biogeography algorithm has good search capability.The simulation results show that compared with the existing methods,this method can effectively reduce the MBPS dimensions,the solving time and the consumed memory.A new method of key protection assessment for power systems based on risk and electrical betweeness is proposed.This method judges the severity of the system caused by the protection's incorrect actions from the perspective of risk,and defines the protection dynamic importance index.The line electric betweeness and node electric betweeness are calculated based on the concept of electric betweeness,which is used to quantify the contributions of the lines and nodes in the power transmission over the system,and defines the protection static importance index.Finally,taking the two index into conisideration,the comprehensive importance index is defined to measured the protection importance in the system,which determines the key protection in the power system.An optimization method for calculating the minimum break protection dependency set based on protection dependency importance is proposed.The MBPS and the MBPDS are all designed to unlock the ring network so that the setting calculation starting point can be determined.The MBPS method disconnects all the protection dependencies in the MBPS.As modern grids become more complex,the number of protection dependencies that need to be disconnected before setting calculation increases sharply,which is unbeneficial for the power system security and stablility.The MBPDS method will greatly reduce the protection dependencies that need to be disconnected when unlocking all simple directional loops.The optimal result is chosen based on the protection dependency importance from all the derived solutions.Thus the optimal setting calculation starting point and the protection setting sequence is determined by the corresponding MBPDS.Example analysis verifies the effectiveness of the method.