Key Technologies Of The Protection For The UHV Half-Wavelength Transmission Line

Half-wavelength AC transmission(HWACT)is an ultra-long-distance AC transmission technology,whose electrical distance is close to half-wavelength at the system power frequency,namely,3000krn(half-wavelength at 50Hz)or 2500km(halfwavelength at 60Hz).Because it has the advantages of no additional reactive power compensation,no need for intermediate switching stations,good economy and reliability,half-wavelength transmission technology has received extensive attention at home and abroad.As an efficient long-distance transmission method,half-wavelength transmission technology will play an important role in the Global Energy Interconnection which advocating international and intercontinental interconnection.As a new type of ultra-long-distance transmission mode,there are still several technical problems to be solved in the half-wavelength transmission line.Relay protection is an important condition for achieving safe and stable operation of half-wavelength lines,and it must be considered in the process of building halfwavelength lines.This paper focuses on the key issues of relay protection for halfwavelength transmission lines.Firstly,the theoretical maximum transmission capacity of the half-wavelength transmission line and the electric characteristics are studied.The key problems to be solved by the half-wavelength line protection are clarified.The calculation effect of the Bergeron equation in the transient process of the halfwavelength line is verified.This paper also introduces the physical simulation method of half-wavelength lines.Due to the long transmission distance of the line,the electrical characteristics of the half-wavelength line are quite different from the existing UHV lines.Conventional over-voltage protection cannot meet the requirements of half-wavelength lines.In response to this problem,this paper deeply analyzes the influencing factors of steadystate over-voltage of half-wavelength lines and proposes an over-voltage protection method suitable for it.The method can accurately calculate the maximum voltage along the half-wavelength line and has good performance.Due to the lack of reliable primary protection method for half-wavelength lines,this paper analyzes the problems of split-phase current differential protection based on Bergeron model in half-wavelength lines,and proposes a multiple reference points based current differential protection modified algorithm.In addition,based on the full use of the anti-fault characteristics of half-wavelength lines,a new fault-component based directional protection method for half-wavelength lines is proposed.Theoretical analysis and simulation prove that the proposed protection principles satisfy the speed and selectivity requirements of half-wavelength line which could be used as the main protection of the half-wavelength lines.