Adaptability analysis of differential protection for UHV half-wavelength AC transmission line

Relay protection is one of problems troubling the development of half-wavelength AC transmission technology. This paper modeled the half-wavelength line with the distributed parameter, researched the fault characteristics and the adaptability of phase-splitting steady current differential protection theoretically and through plenty of simulation work, and analyzed its influencing factors from three respects. The result indicates that conventional steady differential protection algorithm is not very suitable for half-wavelength transmission, the sensitivity of middle range is the biggest problem. Then adaptability of zero sequence current differential protection and differential protection based on deviation of power frequency component are researched, the simulation results indicate they have better sensitivity. The research result shows the differential protection can be set as backup protection, and need to coordinate with the quick protection which protect the range close to two ends.