Research On 10kV Distribution Network Deep Current Limiting Adaptive Reclosure Technology

When the traditional auto reclosing mode is used in the distribution network,the short-circuit current will not only make the working conditions of the circuit breaker worse,but also cause great impact on the system.Especially with the extensive use of cables in the domestic distribution network,a large number of hybrid lines coexisting with overhead lines and cables have emerged,and the reclosing failure rate of traditional auto reclosing has increased,which makes the advantage of auto reclosing in improving the reliability of power supply unable to be fully exerted.Therefore,it is of great significance to study an adaptive reclosing technology to judge whether there is any fault on the distribution line before reclosing.In this paper,an adaptive reclosing scheme of deep current limiting distribution line is proposed,that is,putting the impedance probe into operation when the fault occurs,and using the current amplitude passing through the impedance probe to distinguish the transient fault and the permanent fault.From three aspects:the proportion of resistance,the depth of current limiting and the demand of instantaneous and permanent fault judgment,the selection of resistance value of the impedance component is analyzed theoretically.Based on the appropriate resistance value of the trial impedance element,a permanent fault criterion is proposed,that is,when the current amplitude through the main switch and the trial impedance element circuit is greater than the set value,it is a permanent fault,otherwise it is a transient fault,so as to achieve adaptive reclosing.Based on PSCAD/EMTDC simulation software,the distribution line model is established,and the effects of load characteristics,inrush current and low voltage off grid on fault criterion are studied.The results show that the effect of load characteristics on the fault criterion can be eliminated by properly modifying the resistance value of the trial impedance element obtained from the theoretical analysis;the short-circuit current and inrush current can be effectively distinguished by adding 0.3s delay in the fault criterion;when the load rate is large,the trial impedance element will lead to low-voltage off grid of the sensitive load,which will flow through the main break in case of transient fault Circuit breaker-test the current reduction of the impedance element circuit,which will not affect the fault criterion.Through the establishment of distribution network system model,the simulation analysis of transient and permanent faults of three-phase and two-phase phases of pure overhead line,pure cable line and hybrid line in different fault positions and with different transition resistance is carried out,and the validity and feasibility of the proposed permanent fault criterion are verified.This paper discusses two specific methods to design the test impedance element of the core reactor and air core reactor.It is concluded that the size of the air core reactor with the same impedance value is far smaller than that of the core reactor.Finally,the air core reactor is chosen to realize the test impedance element.