1MAC309294-MB F Section 4Protection functionsRER620 185Technical ManualFigure 83: Functional module diagram. I_1H and I_2H represent fundamental andsecond harmonic values of phase currents.I_2H/I_1HThis module calculates the ratio of the second harmonic (I_2H) and fundamentalfrequency (I_1H) phase currents. The calculated value is compared with the set Pickupvalue. If the calculated value exceeds the set Pickup value, the module output is activated.Level detectorThe output of the phase specific level detector is activated when the fundamentalfrequency current I_1H exceeds five percent of the nominal current.TimerOnce activated, the timer runs until the set Trip delay time value. The time characteristicis according to DT. When the trip timer has reached the Trip delay time value, the BLK2Houtput is activated. After the timer has elapsed and the inrush situation still exists, theBLK2H signal remains active until the I_2H/I_1H ratio drops below the value set for theratio in all phases, that is, until the inrush situation is over. If the drop-off situation occurswithin the trip time up counting, the reset timer is activated. If the drop-off time exceedsReset delay time, the trip timer is reset.The BLOCK input can be controlled with a binary input, a horizontal communication inputor an internal signal of the relay program. The activation of the BLOCK input prevents theBLK2H output from being activated.It is recommended to use the second harmonic and the waveform basedinrush blocking from the transformer differential protection function 87Tif available.
