Research On Reclosing And Fault Location Method For High-Voltage Hybrid Transmission Line Composed By Cable And Overhead Line

As an important part of the power system,the high-voltage transmission line is responsible for the transmission of electrical energy,connection to the power grid and electrical equipment.The normal operation of the transmission line is the basis for the safe and stable operation of the power system.In recent years,with the widespread application of hybrid transmission lines,the problems of reclosing and fault location of hybrid transmission lines have attracted the attention of many scholars.After fault occurs on the hybrid transmission line,on the one hand,it is necessary to quickly and accurately identify the faulty section,which is conducive to the correct action of reclosing;on the other hand,it is necessary to solve the exact fault distance,which is helpful to speed up the restoration of power supply and reduce economic losses.Therefore,this paper studies the reclosing and fault location methods for hybrid lines.First of all,this paper proposes a hybrid line reclosure scheme based on the change of positive sequence current phase at the connection point.This method derives the expression of the phase change value of the positive sequence current flowing through the connection point of the mixed line before and after the fault in different sections,and analyzes that the corresponding phase change value of the fault in different sections presents different characteristics,thus put forward the criterion of reclosing action.For different types of short-circuit faults,this method can accurately determine the fault section,and the determination result is not affected by the error of the line parameters;for short-circuit faults near the connection point of the mixed line,the fault section can be correctly identified,so that the reclosing can operate correctly,and there is no dead zone.Then,a method to solve the fault distance based on the voltage and current at one end of the system and the current flowing through the connection point is proposed.This method uses the discrimination method in the previous chapter to identify the fault section,and uses the pure resistance properties of the transition resistor in the known fault section to separately derive the calculation formula of the corresponding fault distance when different types of short-circuit faults occur in the system.This method is not affected by factors such as fault location,fault type,and transition resistance,and has a higher ranging accuracy.Finally,this paper proposes a fault location method for hybrid line based on double-end asynchronous data,which can eliminate the effect of double-end data asynchronization in principle.For an asymmetric short-circuit fault,the current and voltage on both sides of the system are used to calculate the fault point voltage,and the out-of-synchronization angle is eliminated by the ratio of the positive sequence voltage component and the negative sequence voltage component,and the fault location function of the hybrid line is constructed based on this.According to the monotonicity of the ranging function,it is known that the function value is only zero at the fault point,so a search algorithm such as dichotomy can be used to solve the fault point.Similarly,for symmetrical short-circuit faults,the ratio of the positive-sequence voltage component to the positive-sequence voltage fault component can be used to eliminate the out-of-synchronization angle,so as to calculate the fault distance.This method has higher ranging accuracy and is not affected by factors such as fault location,transition resistance and out-of-sync angle.