ABB RELION REX640, Technical Manual, Page: 1704 / 1960

U
p
Control voltage
U
s
Set voltage level Band center voltage
U
z
Line drop compensation term
U
ci
Circulating current compensation term
U
rsv
Voltage reduction parameter
U
p
can be directly read in the monitored data U_CTL.
The circulating current compensation term is calculated only in the parallel acting
operation modes "NRP" and "MCC".
Line Drop Compensation (LDC)
The LDC feature is used to compensate the voltage drop along a line or network fed
by the transformer. The compensation setting parameters can be either calculated
if the resistance and reactance of the line are known or measured from the line drop.
I
L
X
L
R
L
U
B
U
L
Load
Figure 917: Equivalent electrical circuit for calculating the LDC term
The compensation parameters
Line drop V Ris (U
r
) and
Line drop V React (U
x
), are
percentage values of U
n
according to the equations.
Line drop V Ris U
I R
U
Line dro
r
CT n
VT n
=
[ ]
=
⋅ ⋅
⋅
[ ]
%
_
_
3
100
1
1
%U
n
p p V React U
I X
U
U
x
CT n
VT n
n
=
[ ]
=
⋅ ⋅
⋅
[ ]
% %
_
_
3
100
1
1
(Equation 374)
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
L
CT n
r x
= ⋅
[ ]
+
[ ]
( )
[ ]
_
% cos % sin
1
100
ϕ ϕ
xU
n
(Equation 375)
I
L
Average of the currents I_A, I_B and I_C
I
CT_n1
Nominal primary current of the CT
U
r
Setting
Line drop V Ris
Table continues on the next page
Control functions 1MRS759142 F
1704 REX640
Technical Manual