ABB REC670 Applications Manual page 393

1MRK 511 401-UEN A
Bay control REC670 2.2 IEC
Application manual
The calculated load voltage U
Main menu/Test/Function status/Control/TransformerVoltageControl(ATCC,
90)/TR1ATCC:x/TR8ATCC:x.
Load voltage adjustment
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:
= + ×
Usetadjust Uset S
a
I Base 2
IECEQUATION1978 V1 EN-US
U Adjusted set voltage in per unit
set, adjust
USet
Original set voltage: Base quality is U
S Automatic load voltage adjustment factor, setting
a
I Load current
L
I2Base Rated current, LV winding
S Constant load voltage adjust. factor for active input
ci
LVAConst1, LVAConst2, LVAConst3 and LVAConst4 )
is shown on the local HMI as value ULOAD under
L
I
L
+
S
ci
n2
Section 14
Control
SEMOD159053-118 v6
(Equation 118)
VRAuto
i (corresponding to
387