30-11-2012, 04:33 PM
Solutions for Smart and Super Grids with HVDC and FACTS
Solutions for Smart and Super Grids.pdf (Size: 2.16 MB / Downloads: 110)
Abstract
Deregulation and privatization are posing new
challenges to high-voltage transmission systems. High-voltage
power electronics, such as HVDC (High Voltage Direct Current)
and FACTS (Flexible AC Transmission Systems), provide the
necessary features to avoid technical problems in heavily loaded
power systems; they increase the transmission capacity and
system stability very efficiently and assist in preventing
cascading disturbances. Environmental constraints, such as
energy saving, loss minimization and CO2 reduction, will also
play an increasingly more important role. The loading of existing
power systems will further increase which will lead to
bottlenecks and reliability problems. Therefore, the strategies for
the development of large power systems go clearly in the
direction of Smart Grids, consisting of AC/DC interconnections
and point-to-point bulk power transmission “highways” (Super
Grid Solutions). FACTS technology is also an important part of
this strategy. These hybrid systems offer significant advantages
in terms of technology, economics and system security. They
reduce transmission costs as well as help bypass heavily loaded
AC systems.
INTRODUCTION
The electric power supply is essential for life of a society,
like the blood in the body. Without power supply there are
devastating consequences for daily life. However,
deregulation and privatization are posing new challenges to
the transmission systems. System elements are going to be
loaded up to their thermal limits, and wide-area power trading
with fast varying load patterns will contribute to an increasing
congestion [1, 2].
In addition to this, the dramatic global climate
developments call for changes in the way electricity is
supplied. Environmental constraints, such as loss
minimization and CO2 reduction, will play an increasingly
important role. Consequently, we have to deal with an area of
conflicts between reliability of supply, environmental
sustainability as well as economic efficiency [3, 4]. The power
grid of the future must be secure, cost-effective and
environmentally compatible [2]. The combination of these
three tasks can be tackled with the help of ideas, intelligent
solutions as well as innovative technologies. The combination
of these three tasks can be solved with the help of ideas,
intelligent solutions as well as innovative technologies.
Innovative solutions with HVDC and FACTS have the
potential to cope with the new challenges. By means of Power
Electronics, they provide features which are necessary to
avoid technical problems in the power systems, they increase
the transmission capacity and system stability very efficiently
and help prevent cascading disturbances.
The vision and enhancement strategy for the future
electricity networks are, for example, depicted in the program
for “SmartGrids”, which was developed within the European
Technology Platform. Features of a future Smart Grid such as
this can be outlined as follows: flexible, accessible, reliable
and economic. Smart Grids will help achieve a sustainable
development.
HVDC AND FACTS TECHNOLOGIES
In the second half of the last century, high power HVDC
transmission technology was introduced, offering new
dimensions for long distance transmission. This development
started with the transmission of power in a range of less than a
hundred MW and was continuously increased.
Transmission ratings of 3 GW over large distances with
only one bipolar DC line are state-of-the-art in many grids
today. Now, there are ways of transmitting up to 6 GW and
more over large distances with only one bipolar DC
transmission system. The first project in the world at a DC
voltage of +/- 800 kV is the Yunnan-Guang project in China
with a power transmission capacity of 5,000 MW. Further
projects with similar or even higher ratings in China, India
and other countries are going to follow.
Prospects of HVDC in China
In China, the 3,000 MW +/- 500 kV bipolar Gui-Guang
HVDC system (Fig. 11) with a transmission distance of
980 km was build to increase the transmission capacity from
west to east. It is integrated into the large AC interconnected
system. In the same system there is also an already existing
HVDC scheme Tian-Guang in operation. Both DC systems
operate in parallel with an AC transmission in this grid.
CONCLUSIONS
In conclusion to the previous sections, Table 1 summarizes the
impact of FACTS and HVDC on load flow, stability and
voltage quality when using different devices. Evaluation is
based on a large number of studies and experiences from
projects. For comparison, mechanically switched devices
(MSC/R) are included in the table.