ABB RELION RET670 Applications Manual page 458

Section 8
Impedance protection
452
fact that all settings are performed in primary values. The impedance transformation
factor is presented for orientation and testing purposes only.
I
V 1200 0.115
= × =
p
KIMP s
I V 5
s p
EQUATION1735 V1 EN-US
The minimum load impedance at minimum expected system voltage is equal to
equation 371.
2
V 380
min
= =
Z
L min
S 1000
max
EQUATION1736-ANSI V1 EN-US
The minimum load resistance R
equal to equation 372.
(
j
= ×
R Z cos
L min L min
EQUATION1338 V1 EN-US
The system impedance Z
two-machine system, see figure 228. Its value is calculated according to equation 373.
= + +
Z Z Z Z
S SA 1 L 1 SB 1
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 229, which is for general case
calculated according to equation 374.
Z
= -
Z S Z
CO SA 1
E
B
+
1
E
A
EQUATION1340 V1 EN-US
In particular cases, when
× =
0.069
400
2
= W
144.4
at maximum load and minimum system voltage is
Lmin
)
= × =
144.4 0.95 137.2
max
is determined as a sum of all impedance in an equivalent
S
( )
= + W
17.16 j 154.8
1MRK 504 163-UUS A
(Equation 370)
(Equation 371)
W
(Equation 372)
(Equation 373)
(Equation 374)
Transformer protection RET670 2.2 ANSI
Application manual