ABB RELION RET670, Applications Manual

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from 20 to 70 percent. Transmission capability increases of more than two times can be
obtained in practice.
IEC06000592-2-en.vsd
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
1
1.5
2
2.5
3
3.5
Degree of series compensation [%]
In
c
re
a
se
i
n
p
o
we
r
tr
a
n
s
fe
r
Power transfer with constant angle difference
Degree of
compensation
Multiple of power over
a non-compensated line
IEC06000592 V2 EN-US
Figure 85: Increase in power transfer over a transmission line depending on
degree of series compensation
Active load sharing between parallel circuits and loss reduction
SEMOD168320-79 v2
A series capacitor can be used to control the distribution of active power between
parallel transmission circuits. The compensation of transmission lines with sufficient
thermal capacity can relieve the possible overloading of other parallel lines. This
distribution is governed by the reactance, while the losses are determined by the
resistance. A properly designed series compensation system can considerably reduce
the total transmission system losses, as shown in figure
86 .
en06000593.vsd
R
L1
jX
L1
-jX
C
Line 1
jX
L2
R
L2
Line 2
IEC06000593 V1 EN-US
Figure 86: Two parallel lines with series capacitor for optimized load sharing and
loss reduction
To minimize the losses, the series capacitor must be installed in the transmission line
with the lower resistance. The size of the series capacitor that minimizes the total
losses is given the following expression:
1 1
2 2
-
=
L C L
L L
X X R
X R
EQUATION1899 V1 EN-US
(Equation 56)
Section 8
1MRK 504 163-UUS A
Impedance protection
210 Transformer protection RET670 2.2 ANSI
Application manual