ABB RELION 670 Series Applications Manual page 104

Section 7
Impedance protection
The impedance transformation factor, which transforms the primary impedances to the
corresponding secondary values is calculated according to equation 16. Consider a fact that all
settings are performed in primary values. The impedance transformation factor is presented for
orientation and testing purposes only.
KIMP
EQUATION1735 V1 EN-US
The minimum load impedance at minimum expected system voltage is equal to equation 17.
Z
L min
EQUATION1736-ANSI V1 EN-US
The minimum load resistance R
equation 18.
=
R
L min
EQUATION1338 V1 EN-US
The system impedance Z
system, see figure 45. Its value is calculated according to equation 19.
=
Z Z
S
EQUATION1339 V1 EN-US
The calculated value of the system impedance is of informative nature and helps determining the
position of oscillation center, see figure 46, which is for general case calculated according to
equation 20.
=
Z
CO
EQUATION1340 V1 EN-US
In particular cases, when
=
E
A
EQUATION1342 V1 EN-US
resides the center of oscillation on impedance point, see equation 22.
98
I
V 1200 0.115
= p × = ×
s
I V 5 400
s p
2 2
V 380
min
= = =
144.4
S 1000
max
Lmin
( )
j
× =
Z cos 144.4 0.95 137.2
L min max
is determined as a sum of all impedance in an equivalent two-machine
S
(
+ + =
Z Z 17.16
SA 1 L 1 SB 1
Z
-
S Z
SA 1
E
B
+
1
E
A
E
B
=
0.069
W
at maximum load and minimum system voltage is equal to
× = W
)
+ W
j 154.8
1MRK 511 364-UUS A
(Equation 16)
(Equation 17)
(Equation 18)
(Equation 19)
(Equation 20)
(Equation 21)
Application manual