Research On The Influence Of Ac System Fault On Hvdc Commutation Failure After Yun-guang Transmission System Commissioning

HVDC technology for Bulk power transmission over long distancss is increasingly used in power systems and AC/DC hybrid transmission system exerts important function in China. With Yun-Guang UHVDC system commissioning, the China Southern Power Grid(CSG) has been a complicated grid with the characteristics of multi-infeed and AC/DC hybrid transmission, the operating mechanism and the electrical features of which are much different from pure AC power system. The extensive application of HVDC brings a series of new theory and technology problem, among which the commutation failure is mose prominent.The CSG simulation model including Yun-Guang transmission system is established using the electromagnetic transient program PSCAD/EMTDC in this paper, which can reflect the commutation process and the AC/DC response characteristics accurately due to the DC system detailed model and the AC system equivalent model.The commutation process of DC system is analyzed, and the commutation failure mechanism and harm are expounded. Then, this paper researches the influence of AC fault features on DC system commutation process with theory deriving, and analyzes the commutation failure difference between Y Bridge and D Bridge due to the converter transformers different connection, and verifies the influence pattern of unbalanced faults and transition resistance on commutation failure with simulation examples.The pattern of commutation failure caused by AC fault is searched via scanning the faults of the whole gird, and the duration time of commutation failure is analyzed. The complexity and particularity of multi-infeed system after Yun-Guang transmission system commissioning are indicated by researching the problems of successive commutation failure and commutation failure caused by AC fault clearing.