ABB RELION REX640 Technical Manual page 1554

Section 9
Control functions
1548
hysteresis limits, a second adjustable delay T2 (Control delay time 2), usually with a
shorter time setting than T1, starts. This delay is used for the control commands within
the same sequence until the recovery of voltage occurs. The delays T1 and T2 can be
selected either with definite or inverse time characteristics. In the inverse time mode,
the operate time depends on the difference between the control voltage and the
measured voltage as shown in
the shorter the operating time. More information on the inverse time operation can be
found in the Timer characteristics
Regulation equation
The simple regulating principle is often complemented by additional features to take
the voltage drop of lines into account (line drop compensation), coordinate the
regulation of parallel transformers and change the voltage level according to the
loading state of the network. The control voltage U
equation
U U U U U
+ + −
=
p s z ci rsv
GUID-F4946E3E-E0A5-409B-A255-4EEBB33E1EFC V1 EN
U Control voltage
p
U Set voltage level (
s
U Line drop compensation term
z
U Circulating current compensation term
ci
U Voltage reduction parameter
rsv
U can be directly read in the monitored data U_CTL.
p
The circulating current compensation term is calculated only in the parallel active
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.
GUID-BCD27593-579A-4E82-8180-043A289C6B6D V1 EN
Figure 813: Equivalent electrical circuit for calculating the LDC term
The compensation parameters Line drop V Ris (U
percentage values of U
n
Equation 345. The bigger the difference in the voltage,
chapter.
Band center voltage )
I
L
R
L
U
B
according to the equations
1MRS759142 C
is calculated according to the
p
(Equation 338)
X
L
U
L
) and Line drop V React (U
r
Technical Manual
) are
x
REX640