ABB Relion 670 series - Page 146

fundamental frequency differential currents and at the same time from the common bias
current.
2. Calculates three instantaneous differential currents. They are used for harmonic, and
waveform analysis. Instantaneous differential currents are useful for post-fault analysis using
disturbance recording
3. Calculates negative-sequence differential current. Contributions to it from both (all three)
power transformer sides are used by the internal/external fault discriminator to detect and
classify a fault as internal or external.
IdUnre
IDMAG_A
2nd
Harmonic
5th
Harmonic
Wave
block
IDA
AND
Cross Block
from B or C phases
OR
IBIAS
TRIPUNRE_A
PU_A
TRIPRES_A
BLK2H_A
BLK5H_A
BLKWAV_A
ANSI05000168_2_en.vsd
a
b
b>a
OR
AND
Cross Block
to B or C phases
AND
AND
AND
BLKUNRES
BLOCK
BLKRES
NOT
CrossBlockEn=Enabled
ANSI05000168 V2 EN-US
Figure 42: Transformer differential protection simplified logic diagram for Phase A
Section 6 1MRK 502 066-UUS B
Differential protection
140
Technical manual