Improvement of internal charging current compensation for transmission line differential protection

In 1980, a PCM differential relay was developed to allow for the increase in charging current through transmission lines incidental to 1000 kV overhead lines and 500 kV underground cable lines in urban areas. This differential relay compensates the charging current so that the sensitivity of its relay may not decline. The authors first applied a hardware circuit for differential operation of each terminal voltage to compensate the charging current, and then applied a modified differential approximation of self terminal voltage based on numerical calculation to compensate the charging current. The PCM differential relay for transmission lines has been greatly improved in performance, making full use of the advantages of new (second generation in Japan) technology applied to commercial relays