ABB RET670 Applications Manual page 215

1MRK504116-UUS C
Application manual
The effect on the power transfer when considering a constant angle difference (δ)
between the line ends is illustrated in figure 77. Practical compensation degree runs
from 20 to 70 percent. Transmission capability increases of more than two times can be
obtained in practice.
Multiple of power over
a non-compensated line
Powe r tra nsfe r with co ns ta nt a ng le diffe re nce
3.5
3
2.5
2
1.5
1
0 0.1 0.2
D e gre e of se rie s c ompe nsa tio n [%]
IEC06000592 V1 EN
Figure 77: Increase in power transfer over a transmission line depending on
degree of series compensation
Active load sharing between parallel circuits and loss reduction
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 78.
-jX
C
R
jX
L1 L1
Line 1
jX R
L2
L2
Line 2
en06000593.vsd
IEC06000593 V1 EN
Figure 78: 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:
0.3 0.4 0.5 0.6 0.7
Degree of
compensation
en06000592.vsd
Section 3
IED application
209