ABB ret650 - Page 203

characteristic for the second time delay follows the similar formulas as for the first
time delay, but the t2 setting is used instead of t1.
Line voltage drop
SEMOD159053-105 v6
The purpose with the line voltage drop compensation is to control the voltage, not
at the power transformer low voltage side, but at a point closer to the load point.
Figure
73 shows the vector diagram for a line modelled as a series impedance with
the voltage U
B
at the LV busbar and voltage U
L
at the load center. The load current
on the line is I
L
, the line resistance and reactance from the station busbar to the
load point are R
L
and X
L
. The angle between the busbar voltage and the current, is
j. If all these parameters are known U
L
can be obtained by simple vector
calculation.
Values for R
L
and X
L
are given as settings in primary system ohms. If more than
one line is connected to the LV busbar, an equivalent impedance should be
calculated and given as a parameter setting.
The line voltage drop compensation function can be turned On/Off by the setting
parameter OperationLDC. When it is enabled, the voltage U
L
will be used by the
Automatic voltage control for tap changer function, TR1ATCC for single control
and TR8ATCC for parallel control for voltage regulation instead of U
B
. However,
TR1ATCC or TR8ATCC will still perform the following two checks:
1. The magnitude of the measured busbar voltage U
B
, shall be within the security
range, (setting Umin and Umax). If the busbar voltage falls-out of this range
the line voltage drop compensation calculations will be temporarily stopped
until the voltage U
B
comes back within the range.
2. The magnitude of the calculated voltage U
L
at the load point, can be limited
such that it is only allowed to be equal to or smaller than the magnitude of U
B
,
otherwise U
B
will be used. However, a situation where U
L
>U
B
can be caused
by a capacitive load condition, and if the wish is to allow for a situation like
that, the limitation can be removed by setting the parameter OperCapaLDC to
On.
1MRK 504 169-UEN A Section 11
Control
Transformer protection RET650 2.2 IEC 197
Application manual