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Reduce the power system with protected power line into equivalent two-machine system with
positive sequence source impedances Z
SA
behind the IED and Z
SB
behind the remote end bus
B. Observe a fact that these impedances can not be directly calculated from the maximum
three-phase short circuit currents for faults on the corresponding busbar. It is necessary to
consider separate contributions of different connected circuits.
The required data is as follows:
400
r
U
kV
=
EQUATION1321 V1 EN-US
Rated system voltage
min
380
U
kV
=
EQUATION1322 V1 EN-US
Minimum expected system voltage under critical system
conditions
50
r
f
Hz
=
EQUATION1323 V1 EN-US
Rated system frequency
400
3
p
U
kV
=
EQUATION1324 V1 EN-US
Rated primary voltage of voltage protection transformers
used
0.11
3
s
U
kV
=
EQUATION1325 V1 EN-US
Rated secondary voltage of voltage instrument
transformers used
1200
p
I
A
=
EQUATION1326 V1 EN-US
Rated primary current of current protection transformers
used
1
s
I
A
=
EQUATION1327 V1 EN-US
Rated secondary current of current protection transformers
used
(
)
1
10.71
75.6
L
Z
j
=
+
W
EQUATION1328 V1 EN-US
Line positive sequence impedance
(
)
1
1.15
43.5
SA
Z
j
=
+
W
EQUATION1329 V1 EN-US
Positive sequence source impedance behind A bus
(
)
1
5.3
35.7
SB
Z
j
=
+
W
EQUATION1330 V1 EN-US
Positive sequence source impedance behind B bus
max
1000
S
MVA
=
EQUATION1331 V1 EN-US
Maximum expected load in direction from A to B (with
minimum system operating voltage U
min
)
(
)
max
cos
0.95
j
=
EQUATION1332 V1 EN-US
Power factor at maximum line loading
max
25
j
=
°
EQUATION1333 V1 EN-US
Maximum expected load angle
2.5
si
f
Hz
=
EQUATION1334 V1 EN-US
Maximum possible initial frequency of power oscillation
7.0
sc
f
Hz
=
EQUATION1335 V1 EN-US
Maximum possible consecutive frequency of power
oscillation
The impedance transformation factor, which transforms the primary impedances to the
corresponding secondary values is calculated according to equation
Section 7
1MRK 505 343-UEN B
Impedance protection
366
Application manual
Summary of Contents for Relion 670 series
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