ABB RELION RET670, Applications Manual

Page: 458 / 1016

fact that all settings are performed in primary values. The impedance transformation
factor is presented for orientation and testing purposes only.
1200 0.115
0.069
5 400
p
s
s p
I
V
KIMP
I V
= × = × =
EQUATION1735 V1 EN-US
(Equation 370)
The minimum load impedance at minimum expected system voltage is equal to
equation
371 .
2 2
min
min
max
380
144.4
1000
L
V
Z
S
= = = W
EQUATION1736-ANSI V1 EN-US
(Equation 371)
The minimum load resistance R
Lmin
at maximum load and minimum system voltage is
equal to equation 372 .
( )
min min max
cos 144.4 0.95 137.2
L L
R Z
j
= × = × = W
EQUATION1338 V1 EN-US
(Equation 372)
The system impedance Z
S
is determined as a sum of all impedance in an equivalent
two-machine system, see figure 228 . Its value is calculated according to equation 373 .
( )
1 1 1
17.16 154.8
S SA L SB
Z Z Z Z j
= + + = + W
EQUATION1339 V1 EN-US
(Equation 373)
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 .
1
1
S
CO SA
B
A
Z
Z Z
E
E
= -
+
EQUATION1340 V1 EN-US
(Equation 374)
In particular cases, when
Section 8
1MRK 504 163-UUS A
Impedance protection
452 Transformer protection RET670 2.2 ANSI
Application manual