Research On Longitudinal Main Protection Of UHV Half-wavelength AC Transmission Lines

As my country's electricity energy demand will continue to grow,and the construction scale of energy centers in the western region is gradually expanding,further ensuring the proportion of renewable energy transmission and consumption has become one of the most urgent tasks in the current power development.Half-wavelength AC transmission technology refers to an ultra-long-distance three-phase AC transmission technology with a power frequency(50Hz)half-wavelength,that is,3000 km.As a long-distance,large-capacity,and economical high-efficiency power transmission method that can meet my country's future energy structure optimization and global energy interconnection needs,half-wavelength AC transmission has many problems to be solved in theory and engineering.This paper takes UHV half-wavelength AC transmission lines as the research object.Firstly,the steady-state voltage characteristics of half-wavelength lines are analyzed by wave propagation theory,and then the short-circuit current of half-wavelength lines is deduced and calculated based on the distributed parameter model,and combined with PSCAD simulation software The results obtained are mutually verified,and the characteristics of the fault current of the half-wavelength line are obtained through analysis.On the basis of the above,some protection principles that are expected to be applied to ultra-high half-wavelength AC transmission lines,such as traveling wave protection,current differential protection,integrated impedance protection,and negative-sequence directional pilot protection,have been studied.The results show that some of the current The protection of UHV lines can be applied to half-wavelength lines,but they will all be affected by distributed capacitance currents,line frequency-dependent characteristics and channel delays.It is necessary to improve the criteria or propose new principles to meet the requirements.Finally,this paper aims at the problem that the action speed of the longitudinal protection based on power frequency is restricted by the algorithm time,and proposes a post-test simulation principle based on the Bergeron model,and analyzes different fault conditions such as fault location,transition resistance and fault initial angle.Research and analysis have been carried out,and it is shown that compared with the existing longitudinal differential protection in terms of ideas and methods,both in terms of quick action and sensitivity,it has significant advantages.The influence of,has important reference significance for the research on the principle of transient protection of half-wavelength AC transmission lines.Aiming at the problem of the reliability of traveling wave protection,based on the analysis of the fault characteristics of the half-wavelength line in the forward and reverse directions,this paper proposes a traveling wave longitudinal connection direction based on the integral ratio of the voltage forward traveling wave and the reverse traveling wave.Protection,and the rapid action logic of this protection method is proposed,which effectively reduces the impact of too long line communication on the rapid action of the protection.A large number of simulation tests show that the traveling wave directional longitudinal protection is not affected by the busbar structure,transition resistance,fault initial angle,fault type,fault location,and can meet the requirements of half-wavelength lines for protection speed and reliability.