ABB RELION 620 Series Technical Manual page 437

1MAC504801-IB E
620 series ANSI
Technical Manual
Charact.
I_D
(from Differential calculation)
I
I_B
(from Differential calculation)
BLOCK
I
bias
BLOCK_OPR_LS
Slope section 2
End section 2
Low trip value
Fault in protected area
(from Differential calculation)
AND
BLKD2HPHAR_A
(from Second harmonic blocking)
AND
BLKD2HPHAR_B
(from Second harmonic blocking)
AND
BLKD2HPHAR_C
(from Second harmonic blocking)
AND
BLKD5HPHAR_A
(from Fifth harmonic blocking)
AND
BLKD5HPHAR_B
(from Fifth harmonic blocking)
AND
BLKD5HPHAR_C
(from Fifth harmonic blocking)
AND
BLKDWAV_A
(from Waveform blocking)
AND
BLKDWAV_B
(from Waveform blocking)
AND
BLKDWAV_C
(from Waveform blocking))
GUID-9FE73954-6391-4EA7-9D7D-93CE832DB212 V1 EN
Figure 197: 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 a motor startup or
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 operation characteristic of the biased low stage is determined by Low trip value, Slope
section 2 and the second turning point setting 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 each phase. When the differential current exceeds the
operating value determined by the operating characteristic, the differential function is
activated. 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 TRIP output is always activated when the OPR_LS output is activated.
Protection functions
OR
AND
OR
AND
OR
AND
OR
AND
AND
AND
AND
AND
AND
AND
AND
AND
Section 4
TRIP
OPR_LS
OR BLKD2H
OR BLKD5H
OR BLKDWAV
431