Risk Analysis of CT Saturation Caused by Aperiodic Components

The intrusion of rail transit stray current into the power grid will cause the DC biasing phenomenon of electromagnetic power equipment such as transformers, which will affect the reliability of the relay protection judgment and the accuracy of the electric energy measurement. The equivalent circuit models is used to derive the mathematical models of the magnetic flux density, the parallel error and the phase error of CT under aperiodic components,and the influence of CT transfer characteristics on the instantaneous over-current protection under aperiodic components is analyzed. The PSCAD/EMTDC is used for simulation research. Analysis and simulation indicate that the aperiodic component of the line current will change the excitation characteristics by changing the bias of the core flux, which will adversely affect the transfer characteristics of CT and the correct operation of the protection. The research results provide a reference for the research on the influence of stray current on the accuracy of relay protection and electric energy measurement.