Analysis Of UHV Entry Characteristics And Impact On The Second And Third Lines Of Jiangxi Power Grid

According to the UHV project construction plan of the State Grid Corporation of China,it is expected that the Yazhong-Jiangxi ±800kV UHVDC project and the Jingmen-Wuhan-Nanchang-Changsha-Jingmen 1000 kV UHVAC loop network project of the Central China Power Grid will be putting into operation one after another in 2021.The structure of Jiangxi power grid will be upgraded from a single Ultra high pressure loop network to an UHV AC/DC hybrid network.The characteristics of the power grid and its operation control will have significant changes.Jiangxi power grid has smaller load,bigger difference between peak and valley,and weaker AC connection with the outside.It is more likely to cause component overload and transient stability problems after large-capacity power is enter into Jiangxi.Therefore,the entry of UHV into Jiangxi puts forward higher requirements for the second and third lines of defense of Jiangxi power grid.This paper takes 2021 UHV AC/DC accessed to Jiangxi power grid as the research background.Based on the planning data of 2021,after entering into Jiangxi power grid,the characteristics of UHV AC/DC power grid are analyzed by PSASP simulation software,and the adaptability and strategy optimization of two and three lines of defense are studied.According to the timing of AC/DC operation,the study of characteristics of UHV AC/DC entering,the DC enter in capability based on receiving end power grid constraints before and after the operation of AC loop network is analyzed from two aspects of power flow constraints and transient stability constraints,and the limit values of DC enter in under different constraints are obtained.By comparing the difference of DC enter in limit before and after the AC loop network is putting into operation.It is concluded that if the extreme operation mode of South transmission of Changnan line is not taken into account,the DC entering limit can be rised 3900 MW.It is verified that the operation of the AC loop network project has greatly improved the DC enter in limit.The control measures adaptability of the second line is studied through the typical simultaneous disconnection of double circuit lines of the same tower and the DC bipolar blocking fault.After the large capacity DC will have entered into Jiangxi power grid in 2021,the results show that existing steady control load shedding is slightly inadequate.It is suggested that the load shedding amount under heavy load mode should be increased to about 1500 MW,and the DC power speed reduction measures should be taken into account.It can ensure that the stability control measures after failure have better adaptability in normal operation mode.It is necessary to pre-control AC and DC power in overhaul operation mode,so that the stability control measures have better adaptability after failureBecause of the third line of defense in Jiangxi power grid is difficult to deal with the stability problems,which caused by the third type of disturbance fault after UHVDC access.The solution of fast operation of low-voltage load-shedding relay is proposed.The low-voltage load-shedding settings after DC crossing fault and middle switch rejection fault are given.The simulation results show that the low-voltage loadshedding relay has good adaptability and reliability.Through researching the coherence of generating units under serious faults,the Jiangxi coherence group is found out.This paper analyses the internal splitting section of Jiangxi power grid,and puts forward to the priority of setting splitting points.