ABB RET670 - Page 666

The calculated load voltage V
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
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.
It is possible to do this voltage adjustment in two different ways in Automatic voltage
control for tap changer, single control TR1ATCC (90) and parallel control TR8ATCC
(90):
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 (90) or TR8ATCC (90) 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 (90) or TR8ATCC (90) block, brings the voltage
setpoint back to Vset.
With these factors, TR1ATCC (90) or TR8ATCC (90) adjusts the value of the set
voltage Vset according to the following formula:
2
L
a ci
I
Vsetadjust Vset S S
I Base
= + × +
EQUATION1978-ANSI V2 EN (Equation 423)
V
set, adjust
Adjusted set voltage in per unit
VSet Original set voltage: Base quality is V
n2
S
a
Automatic load voltage adjustment factor, setting VRAuto
I
L
Load current
I2Base Rated current, LV winding
S
ci
Constant load voltage adjust. factor for active input i (corresponding to
LVAConst1, LVAConst2, LVAConst3 and LVAConst4 )
Section 3 1MRK504116-UUS C
IED application
660
Application manual