Research On Distance Measurement And Location Of Single-Phase Grounding Fault Based On Distributed Distribution Network

Modern distribution network is composed of a large number of underground cables and overhead lines,with complex structure and many branches,and single-phase grounding faults often occur.Correct line selection and accurate location of single-phase grounding fault in complex distribution network has always been a theoretical research hotspot and engineering application problem in power system.The research on fast,accurate,simple and practical grounding fault line selection and location methods for complex distribution network has important theoretical significance and engineering application value for timely troubleshooting and restoring normal power supply,and improving the power supply reliability of distribution network.This thesis presents an innovative method of distance measurement and location in distribution network based on zero sequence current passive high frequency carrier.The principle and idea of this method are as follows:in the distribution network,a certain number of zero sequence current transformers are installed at intervals along each feeder,and the secondary load resistance voltage signal of these distributed zero sequence current transformers is modulated at high frequency to form a high-frequency carrier signal containing feeder zero sequence current information.The secondary load resistance voltage carrier signal can also be called "Zero sequence current carrier signal".The current transformers installed in different(geographical)places along the line are allocated to characteristic carrier frequencies,so these high-frequency carrier signals contain complete information of zero sequence current amplitude,phase-angle and geographical location(installation point of current transformer)of distribution network feeders.The zero sequence current carrier signal at the secondary side of the zero sequence current transformer is self coupled to the line primary feeder,and transmitted to the carrier signal receiver(CVT)installed on the substation bus through the feeder for signal filtering and sorting,feature identification and grounding fault line selection and positioning.Because the energy of the above carrier signal source comes from the line zero sequence current itself,the term "passive" is adopted in this paper to distinguish the other carrier signal generation approaches using external power line communication systems(PLCs).The main contents of this paper are as follows.(1)Summarizes the main principles and methods of single-phase grounding line selection and fault location in distribution network on the basis of consulting Chinese and foreign literatures.This paper classifies the single-phasegrounding fault line selection and location methods into centralized and distributed methods,and points out the shortcomings of centralized and distributed methods.Combining the advantages of centralized and distributed positioning methods,it is proposed to directly carry out high-frequency carrier modulation on the secondary side current of zero sequence current transformer installed along the feeder and use the feeder itself for carrier signal transmission,so as to realize the intelligent real-time monitoring of line zero sequence current distribution information.Since the zero-sequence current carrier signal involves any digital and coding,the requirements for carrier communication channel are not high,which is conducive to practical application.(2)Studies the distribution characteristics of zero sequence current and the fault line selection and fault location criteria suitable for passive high-frequency carrier of zero sequence current fault line selection and location approach in different neutral point grounding situations,namly the isolated neutral point,when the neutral point is grounded,the arc suppression coil with adjustable number of turns is used to realize,neutral point with magnetically controlled reactor grounding,as well as neutral point via small resistor grounding.At last,the concrete implementation scheme of this method is proposed.Zero sequence current transformers are installed in each feeder of medium voltage distribution network,and the corresponding positions of the transformers form each monitoring point.(3)The transmission characteristics of zero sequence current carrier signal along the feeder are studied.According to the theoretical analysis,the distributed circuit is used forsimulation,and the impedance parameters of the earth loop are considered.The overhead line and underground cable are simulated respectively,and the attenuation coefficient of the zero-sequence current carrier signal under load condition is verified,which verifies that the attenuation of the zero-sequence current carrier signal is within the controllable range.Inaddition,a method of zero-sequence current carrier signal enhancement is proposed for weak zero-sequence current carrier signal under high-impedance grounding fault.(4)The MATLAB simulation circuit is established,and the low-voltage experimental model is built.The MATLAB simulation and simulation experiments are carried out for the single-phase grounding fault line selection and location under various distribution network grounding modes,which verify the correctness and feasibility of the proposed method.