grids with higher voltage levels and for
cross-regional interconnections.
Second, flexible DC power transmission.
Flexible DC is now used to connect wind farms
to the grid, transfer high-quality power to city
centres, and create DC networks for remote
regions and islands—these are the main applications. Flexible power transmission improves
the quality of unstable renewable energy in the
grid. For some remote regions characterised by
low and fluctuating loads and long transmission
distances, HVAC and conventional HVDC
power transmission technologies are not technically and economically feasible. Flexible DC
power transmission transports power through DC
lines to remote regions and load islands, supporting local economic development with
emission-free electricity.
Third, multi-terminal DC (MTDC) power
transmission transports electricity from multiple
power sources to multiple load centres. It is more
cost effective than conventional HVDC power
transmission, which links one converter station to
another via HVDC transmission lines or cables.
For example, Tibet has great hydropower
potential and will be an important energy source
for China in the future. However, the existing
power transmission corridor is inadequate, and
the single hydropower station that generates
power from the Jinsha, Lancang and Nujiang
rivers in east Tibet is small. An MTDC system
could be used to transfer power from multiple
plants on the three rivers to multiple receiving
terminals near load centres. Several MTDC
power transmission systems are already in operation in China, Africa, Europe, the USA and
shortly in India. MTDC power transmission
projects will play an important role in future
long-distance and large-capacity power transmission in many countries.
Fourth, superconducting power transmission
has already been demonstrated in power distribution because of its low voltage level and short
power transmission distance. Many countries are
researching its application in long-distance
power transmission. For example, the Netherlands is researching superconducting transmission at a rated voltage of 50 kV, and South Korea
is examining high-temperature applications.
The USA is researching three-phase resistance
and a saturated core high-temperature superconducting fault current limiter using the second
generation of high-temperature superconducting
materials. Superconducting DC power transmission could become a future technology trend. It is
more efficient than superconducting AC because
it loses less power in transmission. It is also more
cost effective than AC at the same transmission
capacity. China and Japan have both carried out
experiments in superconducting DC power
transmission. The Institute of Electrical Engineering at the Chinese Academy of Sciences is
constructing a demonstration project to supply
power to an electrolytic aluminium plant.
Fifth, fractional frequency power transmission
has become a research priority for transporting
large-scale offshore wind power, as it is potentially more cost effective and reliable than alternative technologies. However, research is still at
the theoretical and simulation stage. Although it
does merit deeper study and deployment in real
projects. The technology is a combination of
fractional frequency power transmission and
power electronics, which together have the
potential to produce benefits in terms of system
design, control, capacity, reactive power and
harmonics. Another application for this highly
promising technology is hydropower.
Sixth, half-wavelength AC power transmission
means that the electrical distance of power transmission is close to one power frequency
half-wavelength, i.e. 3,000 km or 2,600 km
ultra-long distance three-phase AC power transmission. A lossless half-wavelength AC line is
like an ideal transformer with a transformation
ratio of −1. Sending-end and receiving-end voltage is at the same level but opposite in phase. It is
suitable for ultra-long distance and ultra-large
capacity power transmission. A.A. Wolf and his
colleagues in the former Soviet Union came up
with the idea of half-wavelength AC power
transmission as early as 1940. Potentially,
half-wavelength AC power transmission has
several advantages over conventional AC power
transmission over long distances—such as no
need for reactive compensation equipment and
Special Report 3: A Study of China’s Technology Revolution
359
cross-regional interconnections.
Second, flexible DC power transmission.
Flexible DC is now used to connect wind farms
to the grid, transfer high-quality power to city
centres, and create DC networks for remote
regions and islands—these are the main applications. Flexible power transmission improves
the quality of unstable renewable energy in the
grid. For some remote regions characterised by
low and fluctuating loads and long transmission
distances, HVAC and conventional HVDC
power transmission technologies are not technically and economically feasible. Flexible DC
power transmission transports power through DC
lines to remote regions and load islands, supporting local economic development with
emission-free electricity.
Third, multi-terminal DC (MTDC) power
transmission transports electricity from multiple
power sources to multiple load centres. It is more
cost effective than conventional HVDC power
transmission, which links one converter station to
another via HVDC transmission lines or cables.
For example, Tibet has great hydropower
potential and will be an important energy source
for China in the future. However, the existing
power transmission corridor is inadequate, and
the single hydropower station that generates
power from the Jinsha, Lancang and Nujiang
rivers in east Tibet is small. An MTDC system
could be used to transfer power from multiple
plants on the three rivers to multiple receiving
terminals near load centres. Several MTDC
power transmission systems are already in operation in China, Africa, Europe, the USA and
shortly in India. MTDC power transmission
projects will play an important role in future
long-distance and large-capacity power transmission in many countries.
Fourth, superconducting power transmission
has already been demonstrated in power distribution because of its low voltage level and short
power transmission distance. Many countries are
researching its application in long-distance
power transmission. For example, the Netherlands is researching superconducting transmission at a rated voltage of 50 kV, and South Korea
is examining high-temperature applications.
The USA is researching three-phase resistance
and a saturated core high-temperature superconducting fault current limiter using the second
generation of high-temperature superconducting
materials. Superconducting DC power transmission could become a future technology trend. It is
more efficient than superconducting AC because
it loses less power in transmission. It is also more
cost effective than AC at the same transmission
capacity. China and Japan have both carried out
experiments in superconducting DC power
transmission. The Institute of Electrical Engineering at the Chinese Academy of Sciences is
constructing a demonstration project to supply
power to an electrolytic aluminium plant.
Fifth, fractional frequency power transmission
has become a research priority for transporting
large-scale offshore wind power, as it is potentially more cost effective and reliable than alternative technologies. However, research is still at
the theoretical and simulation stage. Although it
does merit deeper study and deployment in real
projects. The technology is a combination of
fractional frequency power transmission and
power electronics, which together have the
potential to produce benefits in terms of system
design, control, capacity, reactive power and
harmonics. Another application for this highly
promising technology is hydropower.
Sixth, half-wavelength AC power transmission
means that the electrical distance of power transmission is close to one power frequency
half-wavelength, i.e. 3,000 km or 2,600 km
ultra-long distance three-phase AC power transmission. A lossless half-wavelength AC line is
like an ideal transformer with a transformation
ratio of −1. Sending-end and receiving-end voltage is at the same level but opposite in phase. It is
suitable for ultra-long distance and ultra-large
capacity power transmission. A.A. Wolf and his
colleagues in the former Soviet Union came up
with the idea of half-wavelength AC power
transmission as early as 1940. Potentially,
half-wavelength AC power transmission has
several advantages over conventional AC power
transmission over long distances—such as no
need for reactive compensation equipment and
Special Report 3: A Study of China’s Technology Revolution
359