Digital relay

A digital relay that protects a direct current power system, the digital relay comprising:

• a measurement circuit that measures, as an input current, a value detected by a current detecting device that detects a current flowing in the power system, and outputs the measured value as digital data;
• an output circuit that outputs an operation signal to a switching device that interrupts the power system;
• a display circuit that outputs a display signal to display means;
• and
• a processor that outputs a display signal to the display circuit based on the digital data, and outputs control information to the output circuit, wherein
• the processor samples the digital data at predetermined time intervals and, in addition to performing a measurement process for output to the display circuit, outputs control information for executing a protection process using sampling data obtained by the sampling to the output circuit, and executes the protection process of the power system, and
• wherein the protection process comprises a high speed protection process that needs high speed and a normal protection process that does not need high speed, and the high speed protection process is executed every one sampling, in addition to which the normal protection process is executed at a timing of one cycle in which N times' worth of sampling data are accumulated, with N as an integer of 2 or greater, and the measurement process is performed only at a timing at which M cycles elapse, with M as an integer of 2 or greater.