Development of an Algorithm for Improving the Reliability of Digital Differential Protection in Transient Modes

Abstract

The article considers the problem of improving the differential protection reliability in transient modes with current transformers' saturation. It is noted that in recent years in the power systems there have been repeated some incorrect trips of these protections in transient conditions. Tripping was observed not only during external short circuits, but also during motor starts and external load switching. The digital differential protection models for generator and transformer are developed using MATLAB Simulink. Transient modes are simulated, which confirmed the possibility of incorrect protection tripping during external short circuits and during motor starts and generator switching. To increase the protection reliability, it is proposed to apply blocking principle by the aperiodic (DC) component in the differential current in addition to digital restraining. Modeling the advanced protection operation confirmed the complete exclusion of incorrect trips during external short circuits and maintaining sensitivity to internal damage. The problem of measuring the aperiodic (DC) current component in the current transformer secondary circuits is noted. It can be solved by the use of current converters based on Hall sensors.