In order to simulate the wave propagation process of half wave-length AC transmission（HWACT） lines and the operating characteristics of its connected power grids accurately and simultaneously

we established whole electromagnetic transient simulation model of HWACT and large scale AC/DC hybrid power grid in East China.Moreover

we established the steady-state operation mode

and simulated the steady-state operation characteristics of the HWACT line.By simulating the faults in the HWACT line and the faults of the AC/DC power grid

the transient operating characteristics of the HWACT and its interaction with AC and DC were analyzed.Research shows that the fault of HWACT lines is more serious than fault of power system; the system can be restored to stable operation after the failure.When the fault occurs at both ends of the line

the times of commutation failures are higher.After installing arresters on HWACT lines

the stability of the system can be improved

the times of DC commutation failures can be reduced

and the transmission capacity of the lines can be improved.This paper provides a research method for HWACT technology.