The position of grid-forming inverters is crucial in high-proportion renewable energy power systems. When a fault occurs in the grid-forming inverter’s outgoing line

especially when the voltage drops below the minimum voltage specified by the low-voltage ride-through regulation

significant transient overcurrent can be generated

posing a threat to the safety of the inverter equipment. Therefore

a rapid action protection is necessary to isolate the fault. This paper first analyzes the changes in the control system of a grid-forming inverter with a voltage-current dual-loop control structure at the initial moment of a fault. Then

an equivalent model of the inverter’s connection line is established for the outgoing line of the grid-forming inverter. By using this model

the transient frequency characteristics of the inverter’s terminal voltage after a fault in the outgoing line are analyzed. Based on these characteristics

a distance protection scheme for the outgoing line of the grid-forming inverter is designed for three-phase symmetrical faults and two-phase short circuits. The proposed protection scheme utilizes post-fault transient information

demonstrating excellent speed performance. It is well-suited for grid-forming inverter feeder lines

and the simulation results in PSCAD/EMTDC have verified the effectiveness of the proposed scheme.