| The nonlinear problem of current transformer has always been the focus of experts and scholars at home and abroad.In our country,the current transformer is still based on electromagnetic current transformer,and the problem of core nonlinearity will inevitably occur.In particular,the application of new energy sources,such as wind power generation,is becoming more and more widespread,and the configuration of the transmission line current transformer in wind farm is still selected and calculated by conventional methods.Most of the related research uses a single current to analyze the current transformer,and does not consider the transfer function of the current transformer in the simulation or data processing.Some field data show that large short-circuit current can also be provided on the large wind farm side of the centralized access to the short circuit fault of the sending out line.At the same time,the non-periodic component and the high order harmonic are more important in the short circuit current,which is an important factor causing the saturation of the current transformer,which brings great hidden danger to the microcomputer protection of the transmission lineAiming at the above problems,out of the transmission line fault current component of the wind farm is complex and not easy to quantitative analysis,this paper adopts the software modeling and Simulation in the form of the whole model to build wind farm access system of wind farms,simulation under different fault conditions,analysis of the current transformer iron core saturation process,effect of the influence of nonlinear characteristics of feeders differential protection and distance.According to the simulation results,when the current transformer in the wind farm is sent to the nonlinear working area,it will cause the longitudinal differential protection to be mistakenly moved out of the fault,and the distance protection will not move near the end of the protection area.So in terms of microcomputer protection algorithm,proposed in the longitudinal difference protection device with improved recursive point multiplication algorithm and in the distance protection device when the modified differential equation algorithm measures,through software programming,simulation and data analysis show that the longitudinal differential protection misoperation and distance protection misoperation caused external fault algorithm can effectively avoid the saturation of current transformer,and the action is fast,accurate measurement of impedance,the outgoing line relay protection in fast and reliable guarantee. |
