ABB RELION REX640 Technical Manual page 642

Section 4
Protection functions
636
harmonic content / % of fundamental
Stop value 5. H
hysteresis
Start value 5. H
hysteresis
5 th harmonic block
GUID-D9C39F1B-8F17-4EEA-B740-E9E88B6B69E1 V1 EN
Figure 350: The fifth harmonic blocking limits and the operation when both
blocking and deblocking features are enabled through the Harmonic
deblock 5. setting
Fifth harmonic blocking has a hysteresis to avoid rapid fluctuation between TRUE
and FALSE. The required consecutive fulfillments of the condition can be counted
using the blocking counter. When the condition is not fulfilled, the counter is
decreased (if >0).
Also fifth harmonic deblocking (based on the higher limit, Stop value 5.H, if enabled
with Harmonic deblock 5.) has a hysteresis and a counter which counts the required
consecutive fulfillments of the condition. When the condition is not fulfilled, the
counter is decreased (if >0).
Waveform blocking
The biased low stage can always be blocked with waveform blocking; it cannot be
disabled with Restraint mode. This algorithm has two parts. The first part is intended
for external faults while the second is intended for inrush situations. The algorithm has
criteria for the low-current periods of differential current during the inrush and
external fault.
Blocking reset
All three blocking signals, that is, waveform and the second and fifth harmonic, have
a counter or time limit which holds the blocking on for a certain time after the blocking
conditions have ceased to be fulfilled. The deblocking takes place when the counters
or time have elapsed. This is a normal case of deblocking.
The blocking signals can be reset immediately if a very high differential current is
measured or if the phase difference (angle) between the compared currents is close to
zero (in normal situations, the phase difference is 180 degrees).
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REX640
Technical Manual