| In recent years,with the continuous development of urban distribution network,Cable lines are gradually replacing overhead lines,the structure of the network becomes more and more closer,the extensive using of automation equipment and application of new fault line selection technology making the choice of urban distribution network neutral grounding modes become more complicated.There are two kinds of viewpoints about the development direction of the neutral grounding modes in distribution network in our country: one view advocates the continuous use of the low current grounding mode that mainly uses the arc suppression coil grounding mode;the other viewpoint promotes the use of the low resistance grounding mode.So far,there is no definite standard on how to determine the neutral grounding mode in distribution networks.In addition,with the extensive DG access to the distribution network,the choice of grounding mode and the single-phase grounding fault characteristics need further research.Based on the above considerations,at first this paper analyzes the theory of current and voltage characteristics of single-phase with transition resistance grounding fault and intermittent arc grounding fault under the arc suppression coil grounding mode and the low resistance grounding mode.Taking the actual distribution network of Foshan in Guangdong Province as the research object,the capacity of the arc suppression coil and the resistance values of the small resistance are selected according to the actual parameters.The single-phase grounding fault simulation models under two kinds of grounding modes are established by using PSCAD,the transition resistance grounding and arc grounding fault are simulated respectively,and the protective relaying under two kinds of grounding modes are configured.The essay has put forward how to analysis the tripping–rate model under Petersen coil and low resistance grounding modes when single-phase ground fault happens.Taking only the single-phase ground fault into consideration,while other parts remain normal,the essay tries to analyze the influence on load point reliability from the perspective fault isolation and load transfer respectively.Taking advantage of the minimal path method,this essay also developed two different reliability index based on different grounding modes with regards to the long-term power outage rate,average long-term power outage time,short-term power outage rate and average short-term power outage time.The power supply reliability of Foshan in Guangdong Province was evaluated to provide reference for choosing the grounding modes in urban distribution network.Based on a low resistance grounded distribution network containing IIDG,according to the control strategy of IIDG combined with symmetrical component method,the single-phase earth fault analysis model of upstream and downstream side of IIDG is established,Earth fault point current,sequence fault current,and three phase fault current are analyzed respectively when IIDG’s parallel transformer adopts different grounding modes and finally use PSCAD/EMTDC to build fault simulation model to verify the correctness of the analysis.The conclusions could be provided as reference when choose the grounding modes for IIDG’s parallel transformer and the configuration of protective relaying. |
