Research On Protection Strategy Of HVDC Transmission Lines

In China,the rapid development of economy and other aspects has led to a significant increase in electricity demand.AC transmission loss is large,suitable for short-distance transmission,not suitable for cross-network interconnection.Due to the low cost of the line,DC transmission can transmit power over long distances,which makes the rapid development of DC transmission technology.The rapid increase of transmission distance and voltage level makes transmission loss less,but also causes DC system,DC line and other faults to occur more frequently.In order to improve the reliability,selectivity and sensitivity of the protection,this paper mainly analyzes and summarizes from the following aspects:(1)Mainly summarized and summarized from the aspects of protection configuration and principles,protection principles.According to the line operation requirements,the protection configuration principle is as follows: traveling wave protection as the main line protection,after the traveling wave protection is rejected,the differential undervoltage protection action.When the differential undervoltage protection exits or refuses to operate,the differential protection and low voltage protection start.At the same time,the protection principle of voltage traveling wave protection and differential undervoltage protection are summarized in terms of protection criteria,tuning principle and logic principle,and the operating conditions of differential undervoltage protection are analyzed: differential criterion and undervoltage criterion.Through these two criteria,after the traveling wave protection is rejected,the protection can identify the DC line ground fault.(2)The three engineering cases of a DC line fault at ±800kV Fulong Converter Station,the fault of the pole I pole II of ±800kV Jinping Converter Station,and the fault of the pole I DC line of ±800kV Jinping Converter Station were analyzed.A certain DC line fault at ±800kV Fulong Converter Station,the DC line voltage suddenly drops,the DC line current suddenly increases,and the DC line sudden change protects the action.The fault of the bipolar DC line of ±800kV Jinping Converter Station is due to the lightning voltage causing the grounding grid voltage in the station to rise,and at the same time causing the overvoltage protection breakdown of the pole I and pole II DC voltage divider voltage divider varistor.±800kV Jinping converter station pole I DC line fault,pole protection and sudden amount protection are working correctly.The causes and mechanisms of the occurrence of three failures are described,and suggestions for improvement or precautions are proposed;(3)It mainly analyzes the fault characteristics of DC line,the difference between non-fault lightning and short circuit fault,and the protection configuration method.According to the theoretical analysis,the criterion is established to form a new DC line protection method based on correlation analysis.According to the relationship between fault current and measuring point current,the correlation coefficient is introduced to construct the fault identification criterion based on current correlation.The waveforms of lightning strike and short circuit fault are analyzed,and the correlation function based on voltage quantity is introduced to establish non-fault lightning strike.And the identification criteria of the faulty line,the fault identification criterion based on voltage correlation is constructed.The proposed criterion can judge various fault types,and each criterion is configured together to ensure high reliability of protection,strong resistance to transition resistance,and high protection sensitivity.Based on PSCAD/EMTDC simulation platform,the feasibility of the proposed method is verified.