Line-Drop Compensation U - ABB SPAU 341 C User Manual

Line-drop
compensation U
z
Line drop
compensation
with parallel
transformers
4
The line-drop compensation feature of the volt-
age regulating module SPCU 1D50 compen-
sates resistive and reactive voltage drop of the
line fed by the transformer. Thus the module
can maintain the reference voltage U
end. The compensation parameters to be given,
U and U , are percentage values of U
r x
ing to the following expressions:
√3 x I
x R
nt
U [%] = x 100
r
U
n
√3 x I
x X
nt
U [%] = x 100
x
U
n
I = rated current of the power transformer
nt
U = rated phase-to-phase voltage of the power
n
transformer
R = resistance of the line, Ω/phase
X = reactance of the line, Ω/phase
U [%] indicates the resistive voltage drop of the
r
line, and U [%] the reactive voltage drop of the
x
line. When calculated by the module, the real
compensation value for the voltage drop takes
into account the phase shift of the network and
the measured current. The current is selected
with the software switches.
Line-drop compensation is also possible with
parallel transformers. When the master/slave
principle is used, an unlimited number of power
transformers can be operated in parallel. The
voltage regulating module operating as master,
calculates the voltage drop on the basis of its
own measurements, assuming that the power
transformers are equally loaded. The general rule
for calculating the parameters U
is, that the line and transformer ratings for sin-
gle operation are entered.
When the negative reactance principle is used,
the regulator uses the load phase-shift setting
value and the measured current amplitude as
references for calculating the line drop. The
phase shift measured by the regulator does not
affect the line drop compensation at all. In a
case, where the actual load phase shift is equal
to the setting value, a line drop compensation
with full resistive and reactive compensation is
achieved. When calculating the U
parameters, the resistance and reactance used
in the formulas should be the values of the net-
work in common. I , the rated current of the
nt
If the compensation parameters R and X are
unknown, the voltage can be calculated by meas-
uring the voltage in both ends of the line and
the current and the phase angle of the network.
in the line To ensure that the tap-changer remains in the
s
same position during the measurement, the
accord- module has to be in manual mode.
n
The voltage in the beginning of the line and
the current and the phase angle of the network
can be read on the display of the voltage regu-
lating module.
Then U
the following expressions:
U [%] =
r
U [%] =
x
I = rated current of the power transformer
nt
U = rated phase-to-phase voltage of the power
n
transformer
ϕ = phase shift of the network
U = voltage drop
l0
I = selected current
power transformer, should be the sum of the
rated currents of the transformers operating in
parallel. If the transformer is used in both sin-
gle and parallel operation, the correct line drop
compensation can be established by entering
different setting values for U
main and second setting banks. Switch SGF1/6
can be used to change the setting bank accord-
% and U % ing to the operation mode used.
r x
When the minimizing circulating current
principle is used, the voltage regulating mod-
ules obtain current and phase-shift information
from the other modules. Therefore, they also
hold information about the load distribution
between the power transformers, and the load
phase-shift setting value does not have to be
entered. The compensating parameters U
U % are calculated in the same way as for the
x
negative reactance principle. For the line drop
compensation to work satisfactorily, it is impor-
% and U % tant that the I
r x
each voltage regulating module is set. Switch
SGF1/6 can be used to change the setting bank
according to the operation mode used.
[%] and U [%] can be calculated from
r x
x √3
cosϕ x U I
l0 nt
x
U I
n
x √3
sinϕ x U I
l0 nt
x
U I
n
% and U
r
value and the I
nt
% in the
x
% and
r
/I ratio for
nt ct