ABB RELION 620 Series Technical Manual page 438

Section 4
Protection functions
432
The stage can be blocked internally by the second or the fifth harmonic restraint, or by
special algorithms detecting the inrush and current transformer saturation at external
faults. When the operation of the biased low stage is blocked by the second harmonic
blocking functionality, the BLKD2H output is activated.
The BLKD5H output is activated when the biased low stage is blocked by the fifth
harmonic blocking functionality. Correspondingly, when the operation of the biased low
stage is blocked by waveform blocking functionality, the BLKDWAV output is activated
according to the phase information.
When required, the operating outputs of the biased low stage can be blocked by the
external control signals BLK_OPR_LS and BLOCK.
The operation of the protection relay is affected by the biasing as shown graphically by the
operating characteristic.
I [%Ir]
d
300
200
b2
100
d1
Low trip
value
100
Section 1 Section 2
End section 1
GUID-C43BE0B5-884B-42E8-A549-FDBAFB098BB1 V1 EN
Figure 198: Operation characteristic for biased operation of 87T
The Low trip value setting of the biased stage of the differential function is determined
according to the operating characteristics curve:
Lowtrip value Id
1
=
GUID-8EDE9463-6AB2-4922-B321-6A4F9B159961 V1 EN
d2
200 300
End section 2
1MAC504801-IB E
b3
d3
400 500
Section 3
620 series ANSI
Technical Manual
I [%Ir]
b
(Equation 46)