Abstract: Data from a digitizing unit is stored in a time-series data buffer, via a data receiving circuit. The data on which a digital filtering process is performed by a digital filtering processing circuit is stored in time series in a time-series instantaneous-value data storing circuit. A digital computing unit sets a time of temporally oldest data from among a group of latest time data stored in a latest time-data storing circuit as a reference time, extracts time data having the same time as the reference time from the time-series instantaneous-value data storing circuit, and then performs a digital computation.

Abstract: Data from a digitizing unit is stored in a time-series data buffer, via a data receiving circuit. The data on which a digital filtering process is performed by a digital filtering processing circuit is stored in time series in a time-series instantaneous-value data storing circuit. A digital computing unit sets a time of temporally oldest data from among a group of latest time data stored in a latest time-data storing circuit as a reference time, extracts time data having the same time as the reference time from the time-series instantaneous-value data storing circuit, and then performs a digital computation.

Abstract: A protective relay for a transformer issues a relay tripping command when the differential current that is the difference between currents in the primary and secondary windings of the transformer has a magnitude larger than the specified value and, at the same time, when the differential current includes the fifth harmonic component less than the specified value. Another cause of tripping signal generation is the differential current value processed to have a certain timer characteristics.

Abstract: A current ratio-differential relay for protecting a power system comprises a logical circuit which provides the final output upon determination that the operating force signal is active and the suppressing force signal is inactive. The operating force signal is made active when the scalar quantity of the vector summation of line currents flowing into and out of the bus-bar is larger than a certain value, and the suppressing force signal is made active when the maximum value of scalar quantities of the line currents is larger than the scalar quantity of the vectorially-summed current multiplied by a certain constant. Both signals are supplied to the logical circuit through circuit means having a certain time delay in the restoring operation.

Abstract: A protective relay which generates a signal to protect an object in a power system that is to be protected in response to a differential signal and a suppress signal showing an abnormal condition, which are obtained from electric currents of two separate points in the object. The protective relay is equipped with a logical decision circuit which generates the signal to protect the object only when the differential signal is greater than a predetermined value, and the second harmonic component contained in the differential signal is smaller than a predetermined ratio.

Abstract: A rectifier circuit includes three operational amplifiers, the first of which is provided with feedback loops containing diodes of opposite polarity. The other op-amps are coupled to the output of the first one via the respective diodes, and the outputs thereof are fed back to the inputs thereof and to the input of the input op-amp.

Abstract: A relay adapted for protection of a transformer and capable of functioning with certainty upon occurrence of any internal fault in the transformer but not functioning in the case of an inrush current which flows therein at the time of non-load energization or the like.