Fault Analyis And Application Of Symmetri Cal Component Method In Distribution Network

It is very important to analyze and calculate the asymmetric fault of power system for power system fault analysis and relay protection setting.In its development,it can be divided into two parts:symmetrical component method and phase component method.Under the condition of three phase symmetry of power system,the symmetrical component method can be divided into three phases of positive sequence,negative sequence and zero sequence,and the three order component is independent,the fault calculation is intuitive and simple,so it has been widely used.In the distribution network of China,there are asymmetric power supply structure and unbalanced three-phase load,therefore,it is difficult to avoid the asymmetry of three-phase parameters in the distribution network.Facing the current situation of distribution network,in the application of the traditional symmetrical component method,the positive sequence,negative sequence and zero sequence can't be used to decouple the three phase quantities and lost the meaning of calculation.For this problem,because the phase component is calculated and analyzed directly in phase coordinates,so the problem of decoupling under coordinate transformation is avoided.Therefore,the phase component method can be used to calculate the three phase system directly.But the phase component method in the application is complex steps,a large amount of calculation,take up a long memory time,so the application of phase component method is limited.In view of this,in order to make use of symmetrical component method in power system analysis and calculation quickly and easy,at the same time,it is necessary to avoid the limitation of the symmetrical component method due to the asymmetry of the three-phase power system parameters.In this paper,a method of equivalent transformation of network structure is proposed.In this method,firstly,the asymmetric part of the three-phase parameters in the power network is transformed into a three phase parameter symmetric network structure with some fault.This structure has two changes compared with the original network structure,first,the original fault-free of the power network into a certain fault with the power network,the two is that the network structure outside of the fault port is changed from the original three phase parameter to the three phase parameter symmetric structure.After satisfying the condition of three phase symmetry,that will do the symmetrical component method is used to analyze and calculate the Three-phase parameter symmetric" fault "network.So the application of symmetrical component method in the system of three phase parameter asymmetry is realized.Compared with the phase component method,this method can effectively reduce the computation and improve the operation speed.With the development of economy,the load which is connected to the distribution network increases year by year and the load structure becomes more complex.Therefore,the main reason of the unbalanced three-phase power system is the load unbalance.In this paper,under the premise of the symmetry of three phase parameters of circuit elements mainly analyzes and calculates the unsymmetrical load.The asymmetric load in different cases is transformed by the equivalent structure,make the three-phase asymmetric load is transformed into a three-phase symmetrical load with a certain "fault",and then the symmetrical component method is used to analyze the network.If the power network occurs elsewhere or with multiple faults,the complex fault calculation method can be used to solve the power network parameters.In this paper,the simulation platform is built to calculate the load asymmetry compare with results of algorithm.The accuracy and feasibility are verified by simulation experiments.Finally set up a unified computing model to make the method universal.