1MAC309294-MB F Section 4
Protection functions
RER620 185
Technical Manual
Figure 83: Functional module diagram. I_1H and I_2H represent fundamental and
second harmonic values of phase currents.
I_2H/I_1H
This module calculates the ratio of the second harmonic (I_2H) and fundamental
frequency (I_1H) phase currents. The calculated value is compared with the set Pickup
value. If the calculated value exceeds the set Pickup value, the module output is activated.
Level detector
The output of the phase specific level detector is activated when the fundamental
frequency current I_1H exceeds five percent of the nominal current.
Timer
Once activated, the timer runs until the set Trip delay time value. The time characteristic
is according to DT. When the trip timer has reached the Trip delay time value, the BLK2H
output is activated. After the timer has elapsed and the inrush situation still exists, the
BLK2H signal remains active until the I_2H/I_1H ratio drops below the value set for the
ratio in all phases, that is, until the inrush situation is over. If the drop-off situation occurs
within the trip time up counting, the reset timer is activated. If the drop-off time exceeds
Reset delay time, the trip timer is reset.
The BLOCK input can be controlled with a binary input, a horizontal communication input
or an internal signal of the relay program. The activation of the BLOCK input prevents the
BLK2H output from being activated.
It is recommended to use the second harmonic and the waveform based
inrush blocking from the transformer differential protection function 87T
if available.
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