Increase of sensitivity of current longitudinal differential protection of intersystem power lines

Current longitudinal differential protection is the main protection of overhead power lines. In the classic version of this protection, the tripping algorithm is based on a comparison of phase currents measured in half-sets. They are located at the ends of the protected object, namely at substations. Currently, in most of the combined power systems, there is a difficult situation regarding the reliability and sensitivity of the differential protection of the intersystem lines of the power grid 500 750 kV. According to the data for 2016 2017, the National Energy System of Russia recorded more than 20 cases of longitudinal differential protection failure due to insufficient sensitivity and, as a result, non-selectivity. This problem is associated with the neglect of significant unbalance current due to bias currents of power lines.