OPERATE
OPR_LS
BLKD2HPHAR_A
(from Second harmonic blocking)
BLKD2HPHAR_C
(from Second harmonic blocking)
BLKD2HPHAR_A
(from Second harmonic blocking)
Fault in protected area
(from Differential calculation)
BLKD5HPHAR_A
(from Fifth harmonic blocking)
BLKD5HPHAR_C
(from Fifth harmonic blocking)
BLKD5HPHAR_B
(from Fifth harmonic blocking)
BLKDWAV_A
(from Waveform blocking)
BLKDWAV_B
(from Waveform blocking)
BLKDWAV_C
(from Waveform blocking))
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
AND
BLKD2H
BLKD5H
BLKDWAV
OR
OR
OR
OR
OR
OR
I
Charact.
I
bias
I_D
(from Differential calculation)
I_B
(from Differential calculation)
BLOCK
BLOCK_OPR_LS
AND
AND
AND
OR
Low operate value
Slope section 2
End section 2
GUID-0E927DF9-5641-4CAE-B808-0B75EA09EA95 V2 EN
Figure 209: Operation logic of the biased low stage
The high currents passing through a protected object can be caused by the short
circuits outside the protected area, the large currents fed by the transformer in
motor startup or the transformer inrush situations. Therefore, the operation of the
differential protection is biased in respect to the load current. In biased differential
protection, the higher the differential current required for the protection to operate,
the higher the load current.
The operating characteristic of the biased low stage is determined by Low operate
value, Slope section 2 and the setting of the second turning point of the operating
characteristic curve, End section 2 (the first turning point and the slope of the last
part of the characteristic are fixed). The settings are the same for all the phases.
When the differential current exceeds the operating value determined by the
operating characteristic, the differential function awakes. If the differential current
stays above the operating value continuously for a suitable period, which is 1.1
times the fundamental cycle, the OPR_LS output is activated. The OPERATE
output is always activated when the OPR_LS output is activated.
The stage can be blocked internally by the second or fifth harmonic restraint, or by
special algorithms detecting inrush and current transformer saturation at external
1YHT530004D05 D Section 4
Protection functions
615 series 393
Technical Manual
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