ABB RET670 - Page 366

2 2
min
min
max
380
144.4
1000
L
V
Z
S
= = = W
EQUATION1736-ANSI V1 EN (Equation 293)
The minimum load resistance R
Lmin
at maximum load and minimum system voltage is
equal to equation 294.
( )
min min max
cos 144.4 0.95 137.2
L L
R Z j = × = × = W
EQUATION1338 V1 EN (Equation 294)
The system impedance Z
S
is determined as a sum of all impedance in an equivalent two-
machine system, see figure
160. Its value is calculated according to equation 295.
( )
1 1 1
17.16 154.8
S SA L SB
Z Z Z Z j= + + = + W
EQUATION1339 V1 EN (Equation 295)
The calculated value of the system impedance is of informative nature and helps
determining the position of oscillation center, see figure 161, which is for general case
calculated according to equation
296.
1
1
S
CO SA
B
A
Z
Z Z
E
E
= -
+
EQUATION1340 V1 EN (Equation 296)
In particular cases, when
A B
E E=
EQUATION1342 V1 EN (Equation 297)
resides the center of oscillation on impedance point, see equation 298.
( )
1
7.43 33.9
2
S
CO SA
Z
Z Z j= - = + W
EQUATION1341 V1 EN
(Equation 298)
Section 3 1MRK504116-UUS C
IED application
360
Application manual