DIGITAL PROTECTION RELAY AND THRESHOLD LEARNING METHOD OF DIGITAL PROTECTION RELAY

A digital protection relay (1) includes: an A/D conversion unit (12) configured to sample inputted AC current at regular intervals; a calculation processing unit (13) configured to perform frequency analysis on the basis of a sampled digital value; a control unit (14) configured to inhibit the interruption operation when a proportion of a harmonic extracted by the calculation processing unit (13) is equal to or greater than a threshold set on the basis of a proportion of a harmonic contained in excitation inrush current; and a threshold learning unit (15) configured to, when excitation inrush current flowing through the transformer has occurred, calculate an update value for the threshold on the basis of a harmonic content rate of a harmonic contained in the excitation inrush current that has occurred.