~
Load
R
L
X
L
U
B
U
L
U
B
R
L
I
L
jX
L
I
L
Re
IE C06000487-2-en.vsd
IEC06000487 V2 EN-US
Figure 153: Vector diagram for line voltage drop compensation
The calculated load voltage U
L
is shown on the local HMI as value ULOAD under Main menu/
Test/Function status/Control/TransformerVoltageControl(ATCC,90)/TR1ATCC:x/
TR8ATCC:x.
Load voltage adjustment
SEMOD159053-118 v6
Due to the fact that most loads are proportional to the square of the voltage, it is possible to
provide a way to shed part of the load by decreasing the supply voltage a couple of percent.
During high load conditions, the voltage drop might be considerable and there might be
reasons to increase the supply voltage to keep up the power quality and customer
satisfaction.
It is possible to do this voltage adjustment in two different ways in Automatic voltage control
for tap changer, single control TR1ATCC and parallel control TR8ATCC:
1. Automatic load voltage adjustment, proportional to the load current.
2. Constant load voltage adjustment with four different preset values.
In the first case the voltage adjustment is dependent on the load and maximum voltage
adjustment should be obtained at rated load of the transformer.
In the second case, a voltage adjustment of the set point voltage can be made in four discrete
steps (positive or negative) activated with binary signals connected to TR1ATCC or TR8ATCC
function block inputs LVA1, LVA2, LVA3 and LVA4. The corresponding voltage adjustment
factors are given as setting parameters
LVAConst1
,
LVAConst2
,
LVAConst3
and
LVAConst4
.
The inputs are activated with a pulse, and the latest activation of anyone of the four inputs is
valid. Activation of the input LVARESET in TR1ATCC or TR8ATCC block, brings the voltage
setpoint back to
USet
.
With these factors, TR1ATCC or TR8ATCC adjusts the value of the set voltage
USet
according
to the following formula:
2
L
a ci
I
Usetadjust Uset S S
I Base
= + × +
IECEQUATION1978 V1 EN-US (Equation 121)
U
set, adjust
Adjusted set voltage in per unit
USet
Original set voltage: Base quality is U
n2
S
a
Automatic load voltage adjustment factor, setting
VRAuto
Table continues on next page
1MRK 511 358-UEN A Section 13
Control
303
Application manual
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