Energy and Power Engineering, 2013, 5, 1293-1297
doi:10.4236/epe.2013.54B245 Published Online July 2013 (http://www.scirp.org/journal/epe)
Research on the Long-distance Transmission
Xueli Wu1, Xiuyuan Yang1, Hong Shen2, Qinyong Zhou2
1Shool of Automation Beijing Information Science and Technology University, Beijing 100192, China
2China Electric Power Research Institute, Beijing 100192, China
Received March, 2013
ABSTRACT
In view of the imbalanced distribution of power load and resources, including the status of “electric shortage” in some
cities in our country, the article discusses the long-distan ce tran smission techno log y. It mainly analyzed two ways of the
long-distance transmission: UHV AC transmission and UHV DC transmission. The fractional frequency transmission
technology and half wavelength AC transmission technology of AC transmission are introduced. Some key technolo-
gies of long-distance transmission are described. It has a guess for long-distance transmission future direction.
Keywords: Energy; Long-distance; Ultra-high Voltage (UHV); Alternating Current (AC); Direct Current (DC);
Transmission
1. Introduction
According to the requirements of the development of
China's national economy, the national power generation
capacity of 1100-1200 GW plan is expected to be real-
ized in 2020. China's current situation analysis, energy
and electricity load in the geographical distribution of ex-
eme imbalance, according to the latest data, about 68%
of the hydropower resources in China located in the
southwest region, about 76% of the coal resources dis-
ibution in the north or the northwest of China, and about
70% of the electricity load is mainly concentrated in the
eastern coastal areas [1-5]. The situation is shown in
Figure 1.
More and more serious with the consumption of
resources, a lot of our region have been facing the risk of
resource depletion, coal resources is an important
resource for thermal power, coal shortage has caused
Figure 1. Resources and electricity load distribution.
some of our cities face a “shortage” dilemma, serious
impact has an affect of the residents’ production and liv-
g. But the development of nuclear power, wind power,
hydropower and other new energy can significantly
reduce the proportion of thermal power. As in Sweden,
nuclear power and hydropower accounted for 70% of the
proportion. And by the end of 2008, the installed
capacity of wind power in China has more than 10
million kilowatts capacity. If this part of wind power
transfer out through long-distance transmission, can not
only solve the problem of "shortage", but also make a
great contribution for scheme s of grid interconnection
and “North to South".
As the adjusting of the strategic approach in our
country, just like “development of the western region”,
“West to East”, to promoting the implementation of the
policy. Making large-capacity, and the imminent application
of long-distance power transmission technology, high-
apacity, high reliability combined power syste m is bound
to become the future development direction. Therefore,
high pressure, long-distance power transmission technology
has become an integral part of grid technology.
2. Long-distance Transmission Mode
According to the long distance transmission, in order to
solve the long-range, high-capacity transmission process,
the article put forward the UHV transmission techno logy.
The transmission capacity of 500 kV voltage level is
about 1000-1500 MW, and the transmission distance is
about 300-1000 km [5], then it’s not able to fulfill the
requirements of the grid no matter on the length, the ca-
city of the transmission, or limit the short-circuit current.

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Based on the issues above, in April 2005, the Chinese
Society of Electrical Engineering, China Machinery
Enterprise Confederation and the China Power Engineerg
Consultants Group Corporation jointly organized discussion
of UHV AC and DC standard voltage clear of AC UHV
nominal voltage 1000 kV, the highest voltage for equip-
ment 1100 kV; UHV DC rated voltage 800 kV[3].
Paragraphs in the national network of UHV transmission
grid transmission capacity of about 5-20 GW, conveying
distance of about 600-2000 km as the choice.
2.1. UHV AC Transmission Technology
As the long-distance transmission with the long-distance
and high-capacity, the State Grid Corporation has at the
end of 2004 to accelerate the construction of UHV power
grid in order to the 1000 kV exchange system as the core
of a strong national grid as a strategic objective. UHV
AC transmission technology can solve the regional
power grid interconnection trunk system increased trend
of increase brought the system unstable and short-circuit
level, reduce transmission losses and efficient transmis-
sion, This paper briefly describes AC Transmission
Fractional Frequency Transmission and a half-wave-
length AC transmission technology.
2.1.1. Fractional Frequency Transmission Technology
In traditional power transfer process, generally used to
change the voltage level of the way to achieve long-
distance and large-capacity transmission, and subfrequency
transmission technology is selected under the conditions
of the lower frequency transmission by changing the
frequency of the electrical energy in the transmission
process, and at higher electricity frequency, i.e. the
frequency of electrical energy in the control conveying
process in order to improve the energy transfer due to the
conveying distance is too large power loss and other
problems.
Fractional Frequency Transmission diagram is shown
in Figure 2. You can see from the chart that the fre-
quency generator issue 50/3 HZ the electrical energy in
the process of transmission keep 50/3 HZ frequency un-
changed until the transmission end of the frequ ency mul-
tiplier frequency adjustment 50 HZ frequency power
system power supply to the Public. Compared with the
traditional power transmission frequency with 50 HZ, the
frequency 50/3 HZ theoretically line transmission capac-
ity can reach three times that of the former, can
Figure 2. Fractional Frequency Transmission schematic
diagram.
reduce the number of transmission circuits and an area of
the corridor [6].
Xifan Wang, the professor of Xi'an Jiao tong Univer-
sity, pointed that the Hydro-generators speed is low, for
giving low-frequency power, simply reduce the number
of pole pairs. Hydro-generators can transformer core area
by increasing the number of turns to achieve the decrease
in energy frequency issued [9-10].
Fractional Frequency Transmission critical frequency
multiplier, the double main control system is AC - AC
inverter circuit, to join AC - AC converter, however,
presents a lot of problems; the problem which usually
appears is that the inverter thyristor guide passes to cause
the failure. To solve this problem [7-8], analysis the lit-
erature on the single bridge and other bridge arm not
conducting both cases for Fractional Frequency. Ac-
cording to the probably problem of transmission fre-
quency converter for the divider, required to strengthen
the developed of the frequency multiplier control system.
2.1.2. Half-wavelength the A C transmissi o n [ 11-13]
The half-wavelength AC transmission refers to the
transmission of electrical distance of nearly a half-wave
power frequency, frequency 50HZ electrical energy
situation for our workers, and the half-wave transmission
distance of 3000 km. With a high degree of social and
economic development, can not deny that the future of
electricity transmission is transnational and even
intercontinental, that 3000 km ultra-long-range transmis-
sion technology has higher practicality.
The 3000km distance of half wavelength transmission
of natural distance, and not in the long-distan ce transmis-
sion process every time to ensure the transmission
distance is precisely 3000km, when the transmission
distance of more than or less than 3000km manual tuning
technology need to take the actual line is tuned into a
half-wavelength . Currently used in two ways: to increase
the series inductance and shunt capacitance, only
increase the shunt capacitance. Wherein, in the same
over-voltage conditions, and the latter can transmit more
power, when a failure occurs at the same time, the power
loss of the former is smaller than the latter, the transient
stability of the latter is preferred.
Literature [11] starting from the half-wavelength
transmission technology, transmission characteristics,
and clarify the advantages of the transmission mode, and
also pointed out that such a transmission line does not
require installation of reactive power compensation
equipment from multiple angles, the reactive power line
capacitance issued by line own inductance consumption.
The literature analysis means half-wavelength AC
transmission failure and its inhibition may occur. Verify
the validity of the transmission mode. The literature [12]
of the half-wave AC Transmission economic argument,
drawn UHV DC transmission, certain funds within the

X. L. WU ET AL. 1295
transmission capacity of 5000MW under the half
wavelength AC Transmission economy better than 800kv
HVDC transmission.
2.2. UHV DC Transmission Technology
DC transmission as the the UHV transmission of a form,
the major powers of the world's electricity currently an
important means to so lve the high -voltag e, high-cap acity,
long-distance transmission and grid interconnection.
Compared to AC transmission, DC transmission, power
generation exchange system and exchange system of
electricity without synchronous operation at both ends of
the exchange system can be run in accordance with their
respective frequency and phase; DC transmission is a
two-wire, all savings supplies, to reduce the loss of
transmission lines, etc..
UHV DC transmission project a 10-year development
plan, China has completed in 2011 and put into operation
the Xiangjiaba - Shanghai 800kV construction. Jinping I
and II power plant are expected to be completed in 2014,
the two power plants to the East China 800kV power
transmission level HVDC Transmission Project [2], the
nominal voltage of UHV DC transmission 800kV. UHV
DC transmission project put into operation in China:
three Chang, three Guang, three Hu Engineerings, have
achieved good results .
HVDC following schematic is shown in Figure 3, the
DC transmission converter station (the rectifier and
inverter stations), DC line, AC side and the DC side
power filter, reactive power compensation device, the
DC reactor which the converter station is the heart of the
DC transmission system, alternating current converted
into direct current through the rectifier equipment
delivered to the receiving end through a DC transmission
line, and through the inverter DC reverse into AC input
AC grid.
Advantages of UHV DC transmission technology:
1) Conserve supplies, direct current transmission is
compared to the two-wire AC. Transmission can save 1/3
of the transmission material.
2) The AC system of generating end and the receiving
end don’t need to run simultaneously, the both ends of
Figure 3. DC transmission schematic.
the AC system can be run in accordance with the
respective frequency and phase, to facilitate adjustment.
3) With respect to the AC transmission compared to
the pollution of the environment and the interference of
the communication device.
3. The Key Technical Issues of the
Long-distance Transmission
3.1. Consolidated Potential Compensation Issues
[16]
Undertake the task of even the receiving end of the
system, and long-distance power plant or a different
partition power system long-distance transmission, long-
distance transmission will cause some inconvenience to
the power system, how the power system to maintain
stability in the effective regulation has been is the key
issue the integrated electric potential compensation
technology proposed fo r this problem.
Integrated potential compensation by the string in the
appropriate place of the long-distance transmission lines
into an amplitude and phase can be adjusted continuously
the potential to achieve a variety of functions needed to
improve the power system operating characteristics. [15]
verified by simulation analysis of the potential
compensation in the transmission process, not only to
improve the static stability of th e system, while also able
to reduce the power of the generator shaft imbalance,
improve the transien t characteristics.
3.2. Overvoltage and Insulation Problems
In the long-distance transmission process, due to the
general use of UHV overhead lines transmission line to
endure operating pressure, fault hazards, lightning impulse
voltage is too high may cause problems, transmission lines
insulation technology is a test. This insulation comprises
two parts: the insulation and on the tower of the power
transmission line of the insulator insulating. Insulation of
transmission lines on the one hand to consider voltage
requirements, on the other hand to consider the economic,
select the correct and economical way to reduce the
voltage level of the equipment is critical to the long-
distance transmission. Domestic overhead line insulators
porcelain insulators, three types of glass insulators and
composite insulators and transmissio n line insulation, the
choice of the insulator also equally important to be
selected according to the specific circumstances of the
transmission.
3.3. Environmental Protection
Long distance transmission of high-voltage, highcapacity
network structure during operation on the inevitable
existence of electromagnetic interference, radio waves,
radiation, corona, and other environmental protection
issues.

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1296
3.3.1. Electromagnetic Radiation
Long-distance transmission of the electromagnetic
radiation is mainly divided into two categories: active
and passive jamming interference, an active interference
mainly from the wires of the corona discharge and the
corona current to the space radiation of electromagnetic
waves, resulting in the in crease of the background noise;
passive interference including high-voltage transmission
lines as great size metal grid to radio signals may
produce secondary radiation, refraction, reflection and
shielding.
Also, China is also an earthquake-prone geographical,
the earthquake happened in Wen Chuan in 2008 has
affected people by now, so the prediction and detection
on earthquake ar e especially important. Seismic observation
stations predict the activity of geological from the subtle
changes of the geomagnetic field. Signals of magnetic
field and DC magnetic field generated by DC transmission
line are difficult to distinguish. If the current or
parameter of the DC transmission line changed, the DC
magnetic field will change too, which may cause
interference to the geological staff, to generate the error
signal.
3.3.2. Corona Interference [14-17]
Corona is decomposed into positively charged ions and
negatively charged electrons due to the gas molecules in
the air when the influence of a strong electric field, the
field strength is further increased when the phenomenon
of electron multiplier, which would form a corona
discharge. Instant corona discharge generates a pulse
current, the current energy in the form of electromagnetic
waves outward release interested around the thus
generated electromagnetic wave radio signal interference,
but also affect the normal work of the high-frequency
carrier channel. The instant of corona discharge will not
only produce electromagnetic interference, also produces
audio interference, irritability serious cau se the surround-
ing reside nt s .
4. Development Prospects
This paper introduces the research status of the long-
distance transmission technology briefly, although the
long-distance transmission are still some problems, but
this is not deter its development and has been widely
used in the curren t long-d istan ce transmissio n techn o logy.
UHV long transmission technology also has improved
steadily, with the forward to the continuous advancement
of science and technology, some technical problems in
the course of transmission will continue to be resolved,
UHV transmission technology will have a good
development. In the context of globalization, with un-
balance of electricity load and the uneven distribution of
resources of international or national, transnational and
even intercontinental transmission may be achieved in
future. Then there will be a major test on core technology
of long-distance transmission.
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