Phase Segregated Current Phase Differential Protection For UHV Transmission Lines

The National Development and Reform Commission (NDRC) and State GridCorporation of China (SGCC) had decided to construct the first UHV transmissionlineofAC 1000kVfrom Jin-southeast toNanyangandthentoJingmen,andit willgointoactionin2008. Itwillpromotethedevelopmentofpowersystemofthenation. Inorder to ensure the UHV transmission lines running stability, a new high-poweredrelayprotectiondevicewithhighreliabilitymustberesearchedanddeveloped.Current phasedifferential protectionwill not beaffectedbypowerswingandtwophase operation condition of transmission line. It is more simple in structure withoutneed of voltage information. But it will seriouslybe affected bydistributed capacitivecurrent of transmission line, and it does not possess Phase Selection function. So thatcurrent phase differential protection can not be used on long UHV transmission lines.SoanovelprincipleofphasesegregatedcurrentphasedifferentialprotectionforUHVtransmissionlinesbasedonBergeronmodelisproposedforthefirsttimeinthispaper.The proposed principle will not be affected by distributed capacitive current and ismore sensitive and reliable than traditional current phase differential protection.Bergeron model is an accurate transmission line model, it is a de-coupled method ofcomputing voltage and current of two points on transmission lines in their normaloperation condition including outside faults of the line. When there are some innerfaultsintherangeoftransmissionline,themodel willbenottrue.Thisdiscriminationcanbeusedtoidentifywhetherthereisfaultinthetransmissionlineornot.Thenovelprinciple has considered the influence of distributed capacitive current, so it does notneed capacitive current compensation. In this paper, method of fault analysis oftransmission lines based on Bergeron model and analysis of protection operation incase of various types of faults are introduced. The paper has also proposed anothernew principle of phase segregated current phase differential protection based on faultcomponent during 1~2 periods after fault inception to improve the ability of bearingtransition resistance. Simulation results by ATP and MATLAB proved that theprincipleiscorrectandhasbestperformanceswhenusedonUHVtransmissionlines.