Search And Safety Control Of Dangerous Lines In Power Flow Transferring And Transmission Section

To improve the real time monitoring and safety control level in power system under line fault trip and normal operating conditions, researches on the search and safety control of dangerous lines in power flow transferring and transmission section are carried out in this paper.Firstly, a fast search method for dangerous lines in power flow transferring resulted from multi branches simultaneous removal based on graph theory and the phase angle of voltage is put forward. The line set which is affected heavily by line disconnection fault is obtained by matrix operation, the equal-phase theory and path search. The power increment of each line in the set is estimated rapidly by direct-current power flow method. The power flow transferring risk index is defined to identify the dangerous lines in power flow transferring with the overload risk.As to the overload lines caused by power flow transferring, a zone-divided and multi control-node emergency control strategy based on power sensitivity is put forward. The power sensitivity matrix between line power variation and nodal injection power variation is derived. The balance machine is involved in the emergency control. The power system is divided into generalized power flow transferring zones according to the network topology. The nodes outside of zone and the zone connection cut point have very close power sensitivity with the lines inside of zone. The computational area is simplified to the generalized power flow transferring zone the overload lines belong to. When the control-node set selected by comprehensive sensitivity makes the overload degree of few overload lines more serious, the multi control-nodes can effectively avoid the power of them increase. With the redundant power of normal lines considered, reverse amount adjustment method and round-trip power prediction method are used to determine the adjustment power, which can avoid the power flow verification effectively. With the local sensitivity calculation and the sparse vector techniques combined, the amount of calculation and memory are greatly reduced.The above two parts are for the monitoring and safety control in power system with line fault trip. To make the monitoring and safety control in the power system under normal operating conditions more targeted and focused, a search method of transmission section based on key lines is proposed. The improved electric betweenness is defined to identify the key lines. Use the weighted power distribution entropy to reflect the effect on load rate distribution and the operation safety level with the key line disconnection, which aims to verify the importance of identified key lines. According to the characteristics of transmission section and power flow transferring zones, considering the constraint of section flow direction and the constraint of tightness between section lines, taking the key line as the main line, search the corresponding transmission section in the power flow transferring zone which the key line belongs to.When the power of some lines in transmission section is close to the maximum transmission power, the operation safety level of power system is reduced. As to this problem, a directional control method of the transmission section power based on power sensitivity and generator re-dispatch is put forward. Calculate the power sensitivity of the lines to all the generator nodes including the balance machine in power system. The balance machine is involved in the transmission section power control. At the basis of the power sensitivity, according to the transmission section power control target, with satisfying the constraints of adjustable output of the generators and line power redundancy, use the nonlinear optimization to get the interface power control scheme, with which the power control targets of the whole interface and each line in the interface are achieved. The method has great improvement in control precision and control ability compared with the former methods.The correctness and superiority of the proposed methods in this paper are verified by a lot of simulations.