The New Principle of New Power System Line Transient Protection Based on Time-Frequency Catastrophe Characteristics

The introduction of power electronic converters has changed the fault characteristics of the traditional power grid. It is difficult for traditional differential protection to meet the protection needs, prone to sensitivity reduction or even the risk of rejection, when the AC line fault occurs. To solve this problem, an AC line protection principle based on the fault full current multi-order mutation was proposed. The protection is based on the regular changes in the waveform deformation characteristics and mutation characteristics of the line on both sides after the fault occurs. Extracting mutation eigenvalues of full current signals on both sides by matrix gradient algorithm. That is the mutation degree of the full current signal on both sides is described. In turn, the longitudinal protection is constructed. The proposed method does not need to extract the power frequency characteristics compared with the traditional fast protection of transient quantities, Solve the problem that the fixed transient quantities cannot be accurately extracted by using the periodic component algorithm under the controlled short-circuit current, and considering the influence of the control strategy of the flexible converter on the protection principle, the protection speed and sensitivity are effectively improved. Finally, the simulation model of the converter grid-connected system is built in PSCAD/EMTDC and the effectiveness of the protection is verified. The proposed protection fault identification time is less than 7.5ms. The proposed protection can better meet the demand of the converter grid-connected line for protection speed and selectivity.