The Constructing of Backup Protections of Overhead Lines Taking into Account the Effect of the Magnetizing Current of the Power Transformers

Abstract

The authors refined the values of phase currents and their harmonic components to calculate the backup protection parameters of overhead lines with branch transformer substations in the regime of turning them on at idle. Despite the significant attenuation of the magnetizing current for the operation moment of the indicated protections, which usually operate with significant time delays, it should be noted that these values are comparable with the operation currents selected on the requirement basis of high sensitivity to fault behind low-power transformers. Analytical dependences of currents on the initial state of transformers and parameters of the electric network are obtained. This allows us to reasonably calculate backup protection settings of overhead lines with branch and intermediate substations, which often allows us to provide the required sensitivity for short three-phase faults on the low voltage side of low-power transformers.