Line drop V Ris U
I R
U
Line dro
r
CT n
VT n
=
[ ]
=
× ×
×
[ ]
%
_
_
3
100
1
1
%U
n
pp V React U
I X
U
U
x
CT n
VT n
n
=
[ ]
=
× ×
×
[ ]
% %
_
_
3
100
1
1
GUID-B79F4E6B-B70E-4D85-BD8C-7877BD52A334 V1 EN (Equation 90)
I
CT_n1
Nominal primary current of the CT
U
VT_n1
Nominal primary voltage of the VT (phase-to-phase voltage)
R Resistance of the line, Ω/phase
X Reactance of the line, Ω/phase
The general LDC equation can be calculated.
U
I
I
U U
z
injected
n
r x
= ×
[ ]
+
[ ]
( )
[ ]
% cos % sin
ϕ ϕ
100
xU
n
GUID-B004A188-862D-4015-868D-8654F8F5D214 V1 EN (Equation 91)
I
injected
Average of the currents I_A, I_B and I_C
U
r
Setting
Line drop V Ris
U
x
Setting
Line drop V React
φ Phase angle between U_A and I_A (ANGL_UA_IA in monitored data)
By default, the line drop compensation (LDC) is not active. LDC is activated by
setting LDC enable to "True". To keep the LDC term within acceptable limits in all
situations, OLATCC has a setting parameter LDC limit, which has a default value
of 0.10 xU
n
. As a result, this gives the maximum value for U
z
in Equation 89.
If more than one line is connected to the LV busbar, the equivalent impedance is
calculated and given as a parameter setting as shown in
Figure 398 for the
equivalent electrical circuit for calculating LDC. For example, if there are N
number of identical lines with identical loads in the substation, the R- and X-values
needed for the settings Line drop V React and Line drop V Ris are obtained by
dividing the resistance and the reactance of one line by N. Because the voltage
drop is different in lines with different impedances and load currents, it is
necessary to make a compromise when setting the Line drop V React and Line drop
V Ris settings. Raising the voltage in the point of lowest voltage must not lead to
overvoltage elsewhere.
By default, the line drop compensation is effective only on the normal active power
flow direction. If the active power flow in the transformer turns opposite, that is,
from the regulated side towards the system in the upper level, the LDC term is
ignored, that is, set to zero. In such a case, it is assumed that the feeding units at the
regulated side of the transformers maintain proper voltage levels. This can cause a
conflict if the transformer tries to reduce the voltage at the substation. Additionally,
1YHT530004D05 D Section 9
Control functions
615 series 735
Technical Manual
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