Research On Fault Analysis Method And Protection Impact Of Complex Fault On The Crossings And Multi-circuit Transmission Lines On The Same Tower

Due to the limitation of the resources of transmission corridors,the phenomenons of multiple transmission lines erected in the same corridor or cross-over between lines are increasing.In recent years,severe weather occurs frequently in the southern region,and the probability of complex faults such as line collision and line collision after line breakage,which occurs on the same tower or cross-over multi-circuit lines,increases greatly.The influence of this complex fault on the system may exceed the original defense standard,or lead to the problem of relay protection refusal or malfunction and enlarge the blackout scope.The existing fault analysis methods and software tools are lack of a general expression and mathematical model of such complex faults,which is not conducive to the scanning analysis and calculation of complex faults at crossing points of power grid.For this reason,this dissertation focuses on the construction of a general model for complex faults of cross-span and multi-circuit transmission lines on the same tower,the short-circuit current calculation and sensitivity analysis of protection based on the above general model,as well as the application of electromechanical transient simulation.The main research contents are as follows:1.Aiming at the complex faults on multi-circuit lines,such as cross lines short circuit,cross lines after breaking or multi-contact fault at the same location,this paper defines multi-fault buses,broken line and non broken line fault ports,connects each phase line of each fault port with the state of fault switches,and constructs a general fault topology which can describe any complex faults of multi-circuit lines.A general description method for any complex faults of multi-circuit lines is proposed.2.According to the states of the switches in the general fault topology,the initial boundary equation matrix of voltage and current is constructed by phase.With the irrelevant variables being eliminated,the boundary characteristic matrix of fault ports under the sequence component is obtained by using symmetric component transformation.Thus the boundary characteristic model of fault ports,which is suitable for any complex faults of multi-circuit lines,is constructed.3.On the basic of the impedance matrix of the nodes at each end of the fault lines and the mutual inductance between the fault lines,the impedance matrix of any fault ports is obtained when the multi-circuit lines are coupled or not.And then the sequence network characteristic model of the fault ports is constructed.The short circuit current calculation of any complex faults of the multi-circuit lines is realized by combining the boundary characteristic model of the fault ports.4.Definining a fault card format suitable for arbitrary complex faults of multi-circuit lines,and using it as the input of the short circuit current calculation program in this paper.The correctness of the short circuit current calculation method proposed in this paper is verified by the simulation with the models such as the same voltage level transmission lines and the different voltage levels ones containing lines on the same tower.Calculating program is used to go through all the complex fault types and to verify the sensitivity of complex faults for main protection and backup protections of cross-over lines in actual power grids.5.By using the fault port boundary characteristic model and the fault port sequence network characteristic model,we can construct the positive sequence additional characteristic model of the fault port,and then obtain the positive sequence additional equivalent circuit cards of the nodes at each end of the fault lines,which is realizing the transient data equivalent description of the complex faults of cross-over and multi-circuit transmission lines on the same tower.Then,the simulation output of the electromechanical transient can be finished by the BPA.The correctness of the positive sequence additional equivalent circuit model is verified by comparing with the electromechanical transient simulation output of the short circuit fault card for double circuit lines in the BPA.