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Since China entered the era of high-voltage AC and DC hybrid power grids, many high-voltage transmission lines have been successfully constructed. Due to the high voltage and long transmission distance of high-voltage transmission lines, once a fault occurs, it will cause serious losses. The research on the relay protection method of high-voltage transmission lines based on time-frequency analysis is proposed, which has important contribution value to ensure the stable development of the power grid. The fault signal of the high-voltage transmission line is extracted based on time-frequency analysis. The fault transient component of a high-voltage transmission line is detected by decomposing the fault signal characteristics. The phase correlation protection based on the fault transient component is realized to realize the relay protection of the high voltage power transmission line. The simulation results show that the accuracy of the proposed method is 100%, which verifies the reliability of this method.

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In order to improve the protection performance of relay protection devices in complex large-scale power grid, a simulation analysis method of relay protection action and weak point adaptability under non preset operating conditions of complex large-scale power grid is proposed. In this method, pscad/emtdc simulation software is used to establish the simulation models of zero sequence and negative sequence directional elements, distance elements and longitudinal current differential elements of relay protection devices. Under the non preset working conditions of complex large power grid, the DC voltage imbalance characteristics, AC and DC power distribution characteristics and fault harmonic characteristics are analyzed, and the adaptability and weak points of relay protection action are analyzed according to these characteristics. The experimental results show that this method is more accurate in obtaining the characteristic value of DC fault under non preset conditions of complex large power grid, and can effectively obtain the action of relay protection devices at different times when non preset conditions occur in complex large power grid and when the setting value of DC low voltage is different. It is concluded that its action adaptability is better when the setting value of DC low voltage is 1.5 kA, and when the setting value of DC low voltage is 5.5 kA and 15 kA, The fault time is short, and the relay protection action has weak points.

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