ABB RELION 670 Series Applications Manual page 372

Section 7
Impedance protection
Reduce the power system with protected power line into equivalent two-machine system with
positive sequence source impedances Z
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:
=
U
r
EQUATION1321 V1 EN-US
U
min
EQUATION1322 V1 EN-US
=
f
r
EQUATION1323 V1 EN-US
=
U
p
EQUATION1324 V1 EN-US
=
U
s
EQUATION1325 V1 EN-US
=
I
p
EQUATION1326 V1 EN-US
=
I
s
EQUATION1327 V1 EN-US
=
Z
L 1
EQUATION1328 V1 EN-US
Z
SA 1
EQUATION1329 V1 EN-US
Z
SB 1
EQUATION1330 V1 EN-US
S
max
EQUATION1331 V1 EN-US
(
cos
EQUATION1332 V1 EN-US
j
max
EQUATION1333 V1 EN-US
=
f
si
EQUATION1334 V1 EN-US
=
f
sc
EQUATION1335 V1 EN-US
The impedance transformation factor, which transforms the primary impedances to the
corresponding secondary values is calculated according to equation 425. Consider a fact that
366
400 kV
=
380 kV
50 Hz
400
kV
3
0.11
kV
3
1200 A
1 A
( )
+ W
10.71 j 75.6
( )
= + W
1.15 j 43.5
( )
= + W
5.3 j 35.7
=
1000 MVA
)
j
=
0.95
max
= °
25
2.5 Hz
7.0 Hz
behind the IED and Z
SA
Rated system voltage
Minimum expected system voltage under critical system
conditions
Rated system frequency
Rated primary voltage of voltage protection transformers
used
Rated secondary voltage of voltage instrument
transformers used
Rated primary current of current protection transformers
used
Rated secondary current of current protection transformers
used
Line positive sequence impedance
Positive sequence source impedance behind A bus
Positive sequence source impedance behind B bus
Maximum expected load in direction from A to B (with
minimum system operating voltage U
Power factor at maximum line loading
Maximum expected load angle
Maximum possible initial frequency of power oscillation
Maximum possible consecutive frequency of power
oscillation
1MRK 505 343-UEN B
behind the remote end bus
SB
)
min
Application manual