Research On Protections Of High-voltage Direct Current Transmission Line Based On The Hilbert-Huang Transform

As High-Voltage Direct Current (HVDC) transmission can transport power inlarge-capacity and long-distance, it is usually used as tie lines among large area grids. Theoperation stability of HVDC transmission line would affect its whole system and theconnected AC grid. Since HVDC transmission line is usually long, it has a high fault rate, soit is very significant for power system to improve the relay protection of HVDC transmissionline.Firstly, the principle of Hilbert-Huang Transform (HHT) is studied in this paper. It isintroduced that the definition of instantaneous frequency, intrinsic mode function, the detailedprocess of Empirical Mode Decomposition, the characteristics of Hilbert-Huang spectrum andsome applications of HHT in power system.Secondly, the transient characteristics of HVDC transmission line fault are illustrated.We can learn that the smoothing reactor and DC filter constitute a physical boundary ofHVDC transmission line, which has a stop-band characteristic to high frequency electrictransient signals. In other words there’s a big difference in high-frequency energy of internaland external faults in HVDC transmission line. Based on that, the HHT can be adopted tocreate a protection criterion for HVDC transmission lines. In the paper, instantaneous energyand Hilbert energy are defined. Then, it proposes an identification criterion for internal andexternal faults based on conspicuous difference of Hilbert energy of transient signals. A largenumber of simulation are performed, results of which show that the proposed identificationalgorithm and program are effective in the case of different fault locations and differenttransition resistance.EMD owns a good mutation point detection capability, and can be used to detect thearrival time of faults travel wave. Finally, an EMD based HVDC transmission line faultslocation algorithm is proposed in this paper. The results of simulation analysis show that itscalculation error is within an acceptable range, and won’t be affected by transition resistance.