ABB REL650 - Page 167

2 2
min
min
max
380
144.4
1000
L
V
Z
S
= = = W
EQUATION1736-ANSI V1 EN (Equation 75)
The minimum load resistance R
Lmin
at maximum load and minimum system voltage is
equal to equation 76.
( )
min min max
cos 144.4 0.95 137.2
L L
R Z
j = × = × = W
EQUATION1338 V1 EN (Equation 76)
The system impedance Z
S
is determined as a sum of all impedance in an equivalent two-
machine system, see figure 76. Its value is calculated according to equation 77.
( )
1 1 1
17.16 154.8
S SA L SB
Z Z Z Z j= + + = + W
EQUATION1339 V1 EN (Equation 77)
The calculated value of the system impedance is of informative nature and helps
determining the position of oscillation center, see figure
77, which is for general case
calculated according to equation 78.
1
1
S
CO SA
B
A
Z
Z Z
E
E
= -
+
EQUATION1340 V1 EN (Equation 78)
In particular cases, when
A B
E E=
EQUATION1342 V1 EN (Equation 79)
resides the center of oscillation on impedance point, see equation 80.
( )
1
7.43 33.9
2
S
CO SA
Z
Z Z j= - = + W
EQUATION1341 V1 EN
(Equation 80)
1MRK 506 334-UUS A Section 6
Impedance protection
161
Application manual