Power transmission line protection method and system based on double-end dynamic system impedance

The invention discloses a power transmission line protection method and system based on double-end dynamic system impedance. The protection method comprises the following steps: circularly recording current and voltage of first time interval data windows at two sides of an accessed power transmission line; when a current sudden change element is started, recording fault current and voltage of second time interval data windows at two sides of the line; calculating power transmission line impedance and new energy equivalent system impedance, taking an imaginary part of the sum of measured value vectors of the line impedance and the system impedances on the two sides as an action vector, taking an imaginary part of the sum of the line impedance and the calculated impedance on the power side of the synchronous machine as a comparison threshold according to a proportionality coefficient, and when the action vector is judged to be greater than a threshold value, judging that an internal fault exists; otherwise, det