Techniques And Applications Of The Staged Protection In Distribution Systems

With the development of distribution network automation and intelligence,the safety and reliability of power supply in China have made great progress in recent years.However,there is still a big gap compared with the developed countries.Distribution system is at the end of the power system,directly responsible for the power supply of users,so it has a decisive impact on the reliability of power supply.With the rapid increase of economy,the requirements for power supply reliability have become continuously stronger.It is urgent to carry out the researches,in order to further improve the reliability,selectivity,rapidity and recovery capability of protection technologies in the distribution network.At present,single-phase ground fault,including high impedance fault,is a common fault type in distribution network,and its fault protection technology has not been effectively solved.There are many problems in the field of distribution network protection,not only because the protection technology and equipment are not perfect,but also because there are many unreasonable aspects in operation and maintenance management.Therefore,in order to solve the problems,the mechanism,strategy,equipment and management mechanism of the whole distribution network fault protection need to be systematically studied and improved.Aiming at the most common types of faults in the current distribution network,this thesis systematically studies the principle and application strategy of the hierarchical and systematic protection technology of the distribution network,and verifies the research content in combination with the demonstration project construction of the actual operation of the distribution network.The innovative research work is as follows:(1)For the limitations of selectivity of current protection strategies,a multi-level configuration method and effectiveness evaluation scheme of short-circuit fault protection of distribution network is proposed,which is with higher reliability and selectivity.The function positioning of the protection levels of circuit breaker at the outlet of the line and the protection levels of segmental switch,branch switch and boundary switch have been studied.By taking full advantage of the optimal coordination of settings and reclosing strategies.the systematic configuration method of staged protection for overhead line and cable ring network is proposed.Furthermore,the design and transformation strategy of distribution network protection device is proposed,and the field application scheme of protection configuration is formed.The evaluation method of the influence of distribution network protection scheme on power supply quality is introduced,which provides a quantitative basis for the rationality and advance of distribution network protection scheme.(2)To solve the weakness of current protection methods when dealing with the complicated conditions of ground fault,like the intermittent fault processe,a staged protection scheme based on the transient direction,waveform similarity and amplitude of small current grounding faults is proposed;In consideration of fault diagnosis reliability and application economy,apply the proposed technology into the staged protection schemes,containing the coorperation of value setting,action time,and automatic reclosing.In this case,the rapid and nearby removal of fault can be realized.For overhead network and cable network with single power source,a method of power supply recovery in non-fault area combining centralized distribution automation system and protection terminal setting is proposed,which provides a systematic solution for fault diagnosis,protection and recovery of small current ground fault.(3)To deal with the high impedance fault happedning in the distribution network with different neutral grounding modes,based on the analyses of fault feature,this thesis proposes the location methods for small resistance grounding system and small current grounding system respectively,by utilizing the high accuracy measurements and the construction of wideband active power factor.By studying the amplitude and distribution of signal characteristics in different systems with the change of transition resistance,the corresponding techniques are proposed to improve the capcability of higher impedance protection.The hierarchical protection and automatic isolation scheme of high impedance faults in distribution network is proposed by combining fault diagnosis technology with staged protection configuration strategy.(4)The engineering practice verifies the correctness,reliability and feasibility of the new staged protection and its automatic isolation scheme for distribution networks.The theoretical method is engineered,and based on the laboratory environment and field tests,a distribution area belonging to Tai’an Power Supply Company is selected for engineering transformation and field demonstration in accordance with the scheme proposed by the research institute for different distribution network frame structures.The practical application fully verifies the correctness and effectiveness of the proposed staged protection scheme for fault diagnosis,automatic isolation and fast recovery of the distribution network,and provided a practical case for further application of the new protection technology and scheme.The application of the research results of this paper can isolate the distribution line faults nearby and quickly,detect and remove the wire falling to the ground and touching the tree faults in time,which is of great significance to improve the reliability of power supply,protect personal safety and prevent electrical fires.