To achieve a more correct regulation, an adjustment to a value of
j
2 slightly less
than -90° (2 – 4° less) can be made.
The effect of changing power factor of the load will be that
j
2 will no longer be
close to -90° resulting in U
L
being smaller or greater than U
B
if the ratio Rline/
Xline is not adjusted.
shows an example of this where the settings of
Rline
and
Xline
for
j
=
has been applied with a different value of
j
(
j
= 30°).
U
B
jI
T
*
Xline
U
L
Xline
Rline
Zline
I
T
I
T
*
Rline
j=30
0
j
1
j
2
D
U
j
1
=11
0
-90
0
=-79
0
en06000630.vsd
IEC06000630 V1 EN-US
Figure 136:
Transformer with reverse reactance regulation poorly adjusted to
the power factor
, the change of power factor has resulted in an increase
of
j
2 which in turn causes the magnitude of U
L
to be greater than U
B
. It can also
be noted that an increase in the load current aggravates the situation, as does also
an increase in the setting of Zline (
Rline
and
Xline
).
Apparently the ratio Rline/Xline according to equation
j
1
must be set with respect to the power factor, also meaning that the reverse
reactance method should not be applied to systems with varying power factor.
The setting of
Xline
gives the sensitivity of the parallel regulation. If
Xline
is set
too low, the transformers will not pull together and a run away tap situation will
occur. On the other hand, a high setting will keep the transformers strongly
together with no, or only a small difference in tap position, but the voltage
regulation as such will be more sensitive to a deviation from the anticipated power
factor. A too high setting of
Xline
can cause a hunting situation as the transformers
will then be prone to over react on deviations from the target value.
There is no rule for the setting of
Xline
such that an optimal balance between
control response and susceptibility to changing power factor is achieved. One way
of determining the setting is by trial and error. This can be done by setting e.g.
Section 12
1MRK 506 375-UEN A
Control
326
Railway application RER670 2.2 IEC
Application manual
Summary of Contents for RELION RER670
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