Research on Single-end Directional Protection for UHV Three-terminal Hybrid DC Transmission Lines Based on T-zone Low and Medium Frequency Attenuation Characteristics as Directional Elements
Protection devices are installed on both sides of the T-zone line,Propose a transient current direction protection method for UHV three-terminal hybrid DC transmission lines.The frequency characteristics of the rectifier side,the T-zone,and the inverter side boundary of the line end of the UHV three-terminal hybrid DC transmission system are analyzed,and it is found the T-zone boundary has a certain attenuation effect on the low-frequency component of the fault current transient signal.Rectifier side boundary and end of line inverter side boundary had a significant attenuation effect on the high-frequency components of the fault current transient signal.Using wavelet decom-position,according to the T zone on both sides of the line transient current in the low-frequency band energy difference to determine the direction of the fault,put forward the fault direction criterion.When the fault occurs on the left side of the T-zone,the high-frequency transient current energy detected at the end of the line and the ratio of the low-frequency transient current energy to discriminate the rectifier side within and outside the fault;when the fault occurs on the right side of the T-zone,the high-frequency transient current energy detected at the first end of the line and the ratio of the low-frequency transient current energy to discriminate the inverter side of the end of the line within and outside the fault;When a fault occurs within the T zone,it is directly determined as an outside zone fault.To give a single-end direction-preserving expansion scheme for UHV three-terminal hybrid DC transmission lines based on the T-zine low and medium frequency attenuation characteristics constituting the directional element,Finally,the PSCAD/EMTDC simulation platform was used to build a model of the Kunliulong UHV three-terminated hybrid DC transmission system and to validate the proposed protection method.The simulation shows that the method proposed in this paper can realize the complete line speed protection of UHV three-terminated hybrid DC transmission lines.
UHV three-terminal hybrid DCtransmission linesT zonehigh and low-frequency energy differences in transient currentsdirection protection
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