Simulation Analysis On The Effect Of AC Side Fault On The Protection Of Yongfu HVDC Transmission System

With the rapid development of HVDC technology, AC-DC hybrid pattern become complex increasingly, AC-DC hybrid system interaction during the fault makes the original fault electrical characteristics change, a factor that led to DC protection action is no longer strictly observed that the protection of accurate and reliable operation when occur DC fault and the protection does not operate reliably when AC fault,while DC protection malfunction leads to DC block and then expand the scope of the accident when AC fault. Tian-Guang HVDC "6.23" incident and the Guangdong Power Grid "6.18 Day" accident, 100Hz protection and DC circuit protection malfunction makes AC and DC interaction for the safe operation of the DC system bring the challenge can not be ignored.Therefore this paper expand a study on that the operating characteristics of the DC system protection when AC fault in Yongfu AC-DC hybrid system, and possible malfunction of the protection proposed improvements, provide a reference for the security and stability of AC and DC mixed-linked system. The main work is as follows:(1) In PSCAD/EMTDC simulation software for Yongfu HVDC system modeling. Yongfu HVDC system for electrical equipment and DC control system in detail modeling, and when AC system of rectifier occur single phase grounding fault、the DC system occur grounding fault near the rectifier and AC system of inverter,we do a detailed simulation analysis of the response charateristics of the control system. the results prove that if failure, the control system can be response failures.reasonably and reliably.(2) A detailed analysis of the factors influencing the commutation failure, the main expand the research on control system and operation methods on commutation failure. In Yongfu HVDC system based on the critical commutation failure transition resistance size expand a lot simulation to study control system and operation mode on commutation failure on,the simulation results show that:the control system on commutation failure seriously affect the extent of having a discrete,the operation mode on commutation failure seriously affect the extent of having less impact severity.(3) AC-DC hybrid system, AC fault occurred caused the current imbalance in the DC transient could lead to bridge differential protection and manifold differential protection malfunction of a detailed analysis and further study the influence of the failure time and DC operational modes on bridge differential protection and manifold differential protection action response and action time exports response,the results showed that:AC fault, manifold differential protection may occur malfunction, bridge differential protection does not occur malfunction, the effect of AC fault occurrence time and DC operation mode on manifold differential protection action response and action time exports response is uncertain.(4) For Yongfu HVDC system traveling wave protection were tested, and expand a study the effects of failure fault resistance and fault distance on traveling wave protection, the test results show that:currently traveling wave protection setting which was used in Yongfu DC transmission system can not distinguish inside and outside the fault, differential undervoltage protection can accurately respond when main protection tripping, DC differential protection can accurately respond when high resistance ground fault, the greater the fault resistance, the longer the distance to fault, the lower the sensitivity of DC protection action.