| The rapid development of economy and society makes the power supply reliability of distribution network more and more people pay attention to it.The configuration and setting of relay protection and distribution automation of distribution network are directly related to the operation safety of distribution network.The research on relay protection of distribution network in our country started late.The branch switch and boundary switch of distribution network are mostly load type,and they do not have the ability to block the fault current.The failure of the traditional distribution network protection line has caused the substation outlet switch to trip.High power outage rate and poor power supply reliability.Due to the large number of grades and complex topology,distribution network protection has not yet had a simple and reliable protection configuration scheme so that it can not only isolate the failure in place to reduce the power outage range,but also achieve all levels of protection to prevent overstepping.Therefore,the design and optimization of a new distribution network protection scheme that is more consistent with the four characteristics of relay protection has become an urgent problem for improving the reliability of power supply in distribution networks.In order to explore a distribution network protection configuration and adjustment scheme that is more in line with the four characteristics of relay protection,this paper carries out research on the basis of Shandong distribution network.The main contents include:analyzing the structure,equipment and protection configuration of Shandong distribution network.According to the characteristics of Shandong distribution network exploring the hierarchical protection scheme,the principle of the arrangement and configuration of the hierarchical protection of Shandong distribution network is designed,and the protection reform scheme of Shandong distribution network is put forward,and the functional comparison between hierarchical protection and traditional protection is carried out with the actual failure case.The main findings are as follows:(1)The parameters and operating data of the distribution network in 16 cities in Shandong Province are collected and analyzed from five dimensions:distribution network structure,branch switch configuration,branch line length,feeder automation,and protection flow limitation.Using a lot of actual data to sum up and analyze the five outstanding characteristics of Shandong distribution network:the structure of the distribution network is clear,the number of branch lines is not large,and the structure has conditions for hierarchical protection;The failure rate of branch line is high,and the local isolation of branch line failure can greatly improve the reliability of distribution network power supply.Most of the lines achieve hierarchical protection without large-scale transformation and have conditions for promotion;The overall feeder automatic configuration rate is still not high,and the ability of fault self-recovery still needs to be strengthened;There are a large number of long lines that limit the load current due to the protection value,which affects the open capacity level and requires the installation of an interstitial circuit breaker.(2)Based on the characteristics and current situation of the Shandong distribution network,combined with seven distribution network fault scenarios,the hierarchical protection action process of the distribution network is envisaged,the design results are extracted,and the concept of hierarchical protection of the distribution network 1s summarized.The hierarchical protection of distribution network includes three levels:local protection,station protection,and regional protection.In-situ protection refers to the local protection of the distribution network branch switch,demarcation switch,etc.,which can achieve the nearest isolation of the distribution network failure.Station area protection refers to substation line switch protection and transformer protection.When on-site protection can not isolate faults,backup protection 1s provided.Area protection refers to the distribution automation system and self-installation,and realizes the overall load reserve and the self-recovery supply of non-fault areas.The main task of hierarchical protection of distribution network 1s to coordinate the role of distribution network protection and distribution automation,straighten out the relationship between main network protection and distribution network protection,improve the selectivity of fault removal,and reduce the power outage area in the shrinking trip range.The basic principle is that the user's failure does not cross the boundary,the branch line failure does not affect the main line,the main line failure does not spread to the area,and the regional failure can be quickly converted for recovery.(3)Further clarify the functional positioning of the switches and systems at all levels of the distribution network,integrate the actual situation of the distribution network with the protection of the main network,and formulate the principle of hierarchical protection allocation and adjustment of the distribution network.Hierarchical protection of distribution network solves the current situation that the fault of distribution network is all due to the line protection trip.The user and branch line configuration circuit breaker switch realizes the near isolation of the failure,and reduces the main Iine trip rate;The middle circuit breaker is used to solve the problem of protection limit load,and the power supply ability is improved.Rational configuration of protection level difference and overlap gate to improve equipment short-circuit resistance and protection selectivity;Make full use of feeder automation system to speed up self-recovery.Based on the principle of hierarchical protection,it meets the actual needs of Shandong distribution network and is feasible,reliable and advanced.(4)According to the actual protection requirements of the Shandong distribution network combined with the hierarchical protection requirements of the distribution network,a detailed implementation plan was formulated from the aspects of optimization,switching and installation,and protection configuration of the distribution network,and a four-step plan for transformation was put forward.In the case of limited investment,the network fault defense capability of 81.6%of distribution lines in Shandong Province can be improved in the short term.In recent years,the protection action of the distribution network in Shandong Province has been counted and compared with the actual cases.In situ protection,site protection,and area protection of hierarchical protection of distribution network are coordinated from spatial dimension,time dimension,and function dimension to minimize the fault impact area.Since the pilot promotion,the correct operating rate of Shandong distribution network protection has increased by 35.7%,reducing the number of power outages in non-fault areas by more than 5.78 million hours,and reducing the loss of power outages by more than 90 million yuan,which has great application prospects. |
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