ADM
A
/D
c
o
n
ve
rs
io
n
s
ca
lin
g
w
ith
C
T
r
a
tio
A
/D
c
o
n
ve
rs
io
n
s
ca
lin
g
w
ith
C
T
r
at
io
P
ha
so
r
ca
lc
u
la
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f
in
di
vi
d
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al
p
h
a
se
c
ur
re
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P
h
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so
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lc
u
la
tio
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f
in
d
iv
id
ua
l p
h
a
se
c
u
rr
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nt
Differential function
IED
D
er
iv
e
e
q
u
a
tio
n
to
c
a
lc
u
la
te
d
iff
e
re
n
tia
l c
ur
re
n
ts
Trafo
Data
P
h
a
so
rs
&
sa
m
p
le
s
P
h
as
o
rs
&
sa
m
p
le
s
Instantaneous (sample based)
Differential current, phase A
Instantaneous (sample based)
Differential current, phase B
Instantaneous (sample based)
Differential current, phase C
Fundamental frequency (phasor
based) Diff current, phase A &
phase current contributions from
individual windings
Fundamental frequency (phasor
based) Diff current, phase B &
phase current contributions from
individual windings
Fundamental frequency (phasor
based) Diff current, phase C &
phase current contributions from
individual windings
Negative sequence diff current
& NS current contribution from
individual windings
ANSI05000166_2_en.vsd
MAX
Settings for Zer. Seq.
Current Reduction
IDMAG_A
IDMAG_B
IDMAG_C
IDMAG_NS
ID_B
ID_A
ID_C
IBIAS
52
152
ANSI05000166 V2 EN-US
Figure 41: Treatment of measured currents within IED for transformer differential function
Figure
shows how internal treatment of measured currents is done in case of a two-winding
transformer.
The following currents are inputs used in the power transformer differential protection function.
They must all be expressed in power system (primary) A.
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
1MRK 502 066-UUS B
Section 6
Differential protection
139
Technical manual
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