ABB REG670 Applications Manual page 562

Section 15
Control
556
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
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
LVAConst2, LVAConst3 and LVAConst4 )
It shall be noted that the adjustment factor is negative in order to decrease the load
voltage and positive in order to increase the load voltage. After this calculation U
will be used by TR1ATCC or TR8ATCC for voltage regulation instead of the
adjust
original value USet. The calculated set point voltage U
HMI as a service value under Main menu/Test/Function status/Control/
TransformerVoltageControl(ATCC,90)/TR1ATCC:x/TR8ATCC:x.
Automatic control of parallel transformers
Control of parallel transformers means control of two or more power transformers
connected to the same busbar on the LV side and in most cases also on the HV side.
Special measures must be taken in order to avoid a runaway situation where the tap
changers on the parallel transformers gradually diverge and end up in opposite end
positions.
Three alternative methods can be used for parallel control with the Automatic voltage
control for tap changer, single/parallel control TR8ATCC:
• master-follower method
• reverse reactance method
• circulating current method
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
I
L
+
S
ci
n2
1MRK 502 071-UEN -
(Equation 271)
VRAuto
i (corresponding to LVAConst1,
is shown on the local
Set, adjust
Application manual
set,