ABB rec670 - Page 454

Assume that we want to achieve that j
2
= -90°, then:
0
1 1
( )
90
0
1
0
1
90
90
j j j
j
j j
j j
+
-
D = ´
ß
D = ´ =
ß
- = +
ß
= - -
j j
j j
V Z I
Ve Ze Ie ZIe
EQUATION1983-ANSI V1 EN-US (Equation 124)
If for example cosj = 0.8 then j = arcos 0.8 = 37°. With the references in figure 181, j
will be negative (inductive load) and we get:
0 0 0
1
( 37 ) 90 53
j = - - - = -
EQUATION1939 V1 EN-US (Equation 125)
To achieve a more correct regulation, an adjustment to a value of j2 slightly less than
-90° (2 – 4° less) can be made.
The effect of changing power factor of the load will be that j2 will no longer be close
to -90° resulting in
V
L
being smaller or greater than V
B
if the ratio Rline/Xline is not
adjusted.
Figure
182 shows an example of this where the settings of Rline and Xline for j = 11°
from figure
181 has been applied with a different value of j
(j = 30°).
Section 14 1MRK 511 401-UUS A
Control
448 Bay control REC670 2.2 ANSI
Application manual