ABB REG670 - Page 143

1. Instantaneous values of currents (samples) from the HV, and LV sides for two-
winding power transformers, and from the HV, the first LV, and the second LV
side for three-winding power transformers.
2. Currents from all power transformer sides expressed as fundamental frequency
phasors with their real and imaginary parts. These currents are calculated within
the protection function by the fundamental frequency Fourier filters.
3. Negative sequence currents from all power transformer sides expressed as
phasors. These currents are calculated within the protection function by the
symmetrical components module.
The power transformer differential protection:
1. Calculates three fundamental frequency differential currents and one common
bias current. The zero-sequence component can optionally be eliminated from
each of the three 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
IDL1MAG
2nd
Harmonic
5th
Harmonic
Wave
block
IDL1
AND
Cross Block
from L2 or L3
OpCrossBlock=On
OR
1
IBIAS
TRIPUNREL1
STL1
TRIPRESL1
BLK2HL1
BLKWAVL1
en06000545.vsd
a
b
b>a
OR
AND
Cross Block
to L2 or L3
AND
AND
AND
BLKUNRES
BLOCK
BLKRES
BLK5HL1
S
w
i
t
c
h
o
n
t
o
f
a
u
l
t
l
o
g
i
c
IEC06000545 V1 EN
Figure 39: Transformer differential protection simplified logic diagram for Phase
L1
1MRK502052-UEN B Section 6
Differential protection
137
Technical manual