Research On Relay Protection And Grid Connection Mode Improvement Of Photovoltaic Grid-connected Substation

With the continuous expansion of the construction scale of photovoltaic power stations in China,more and more photovoltaic power stations are connected to the power grid.Centralized photovoltaic power stations with a scale of 10MW-30MW(hereinafter referred to as photovoltaic power station),are usually made up of several photovoltaic power generation units which are respectively boosted to 35 k V or 10 k V voltage level through the unit boost transformer,gathered from the collection line to the photovoltaic power station busbar and then directly connected to the grid to the 35 k V or 10 k V busbar on the low-voltage side of the substation in the form of a switching station.Due to the different grounding modes of substations and photovoltaic power stations,when the single-phase grounding failure of the grid feeder occurs,it brings many effects to the safe grid connection of photovoltaic power stations and the safe and stable operation of substations.The original relay protection configuration of substations and the grid connection mode of photovoltaic power stations no longer meet the requirements of the safe and stable operation of the power grid and photovoltaic power stations.This article takes a 10 k V photovoltaic power station as the research object.Firstly,it briefly introduces the basic composition and working principle of the photovoltaic power generation system.The influence of photovoltaic power supply,the collection system and line on the zero-order current of photovoltaic power station is elaborated in detail.Then,the theoretical derivation and model construction are conducted,analyzing the implementation method of removing grounding faults in photovoltaic power stations through simulation and verifying the reliability of the built simulation model,which lays a foundation for the subsequent chapter analysis.Secondly,the article gives theoretical analysis of the influence of grounding zero-order current of substation before and after grid connection of photovoltaic power stations,and elaborates the configuration and setting principles of zero sequence overcurrent protection for photovoltaic power stations.Through example setting and simulation,it is shown that after the photovoltaic power station is connected to the grid,there is mutual influence between the photovoltaic power station and the substation.The original substation relay protection configuration and the grid connection mode of the photovoltaic power station have certain limitations.Finally,two improvement schemes are proposed based on the relay protection configuration and grid connection mode of photovoltaic power stations.The relay protection configuration of substation feeder and gridconnected line are improved.Feeder protection is used to remove the singlephase ground fault of the line and grid-connected line protection is used to realize effective backup protection and the grid connection mode of photovoltaic power stations is improved.The isolation transformer is added at the busbar side of grid connection line of photovoltaic power stations to effectively isolate the two different grounding modes to eliminate mutual influence.Moreover,simulation is verified in PSCAD4.6 simulation software to demonstrate the effectiveness of the two improvement schemes.