Download Analysis on the Electromagnetic Environmental Factors of 500kV

Advanced Materials Research
ISSN: 1662-8985, Vol. 599, pp 884-887
doi:10.4028/www.scientific.net/AMR.599.884
© 2012 Trans Tech Publications, Switzerland
Online: 2012-11-29
Analysis on the Electromagnetic Environmental Factors of 500kV
Double Circuit Transmission Line
Jianzhao Qi1, a, Jingyi Li2, b
1,2
Hebei Electric Power Design ＆ Research Institute, Shijiazhuang, 050031, china
a
[email protected], [email protected]
Key words: 500 kV transmission line, frequency magnetic field strength, environmental factors
Abstract. This paper calculates frequency magnetic field strength by the Ampere's law, and
analyzes the main factors affecting the electromagnetic environment of the 500kV Double Circuit
Transmission Lines. In the same electromagnetic transmission line calculation parameters,
optimization of phase sequence can effectively reduce the frequency magnetic field strength; with
the increase of the distance, the line frequency magnetic field strength significantly reduces away
from the center line within 25m. Finally, the paper obtains the phase sequence arrangement with
minimal impact on the electromagnetic environment and the minimum ground clearance meeting
the environmental requirements.
Introduction
With the rapid development of China's economy and urbanization, the rapid growth of the power
load to accelerate the development of power industry, power grid construction as part of the electric
power industry development in recent years, the national power shortage situation to the
development of power grid construction provides a good platform, more and more large power
transmission facilities into the cities, villages, closer to people's daily lives. The operation of the
power transmission project to bring modern civilization to today's society, but also accompanied by
a special, invisible pollution - electromagnetic radiation pollution. In recent years, this pollution has
caused widespread concern of the community, so find out the actual electromagnetic radiation
pollution extent and scope of the high-voltage power transmission project run, and propose effective
control measures to reduce radioactive contamination, do a good job of high-voltage transmission
and transformation electrical engineering environmental protection work is essential. This paper
investigated the impacts of the transmission line height and the phase sequence arrangement on the
electromagnetic fields of the 500kV double circuit transmission lines.
Method of investigating the electromagnetic environmental impact of 500kV double circuit
transmission lines
Regulations of the power frequency electromagnetic field in china
Potential gradient to the earth is formed by overhead transmission lines and then
electromagnetic induction is generated. The main theory of this phenomenon is based on the
Maxwell electromagnetic theory, that is, the variable current generates magnetic field around it over
time. So, the variable magnetic field generates electric filed over time and the variable electric field
produces magnetic filed over time as well. Electric field and magnetic field can transfer into each
other and spread in space to form electromagnetic waves. Magnetic field could be formed around
transmission lines when in operation. The impacts are produced on the surrounding environment
through electromagnetic induction.
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Advanced Materials Research Vol. 599
885
The current Chinese national regulatory standard for the power frequency magnetic field is
based on recommended environmental protection guidance. “Technical Regulations on
Environmental Impact Assessment of Electromagnetic Radiation Produced by 500kV Ultra High
Voltage Transmission and Substation Power Project” (HJ/T 24-1998).This guidance adopts a power
frequency magnetic field of 0.1 mT as the criteria to evaluate the safety for the residential areas. To
ensure the safe operation of transmission and distribution facilities and to protect the public interests,
the state issued a guidance entitled “Code for Design 110kV~750kV Overhead Transmission
Line”(GB 50545-2010).This standard provides the requirement of the safe distance between the
500kV transmission lines and residential buildings.
Electromagnetic mathematic model for the 500kV double circuit transmission line
Based on the quasi-static characteristics of the electromagnetic properties, the magnetic field of
a transmission line is only formed by the electric current. Applying the Ampere’s law, the magnetic
field around the line can be calculated by vector superposition as shown below.
H=
I
2π h 2 + L2
（1）
Where: I is the current value of ith line，h is vertical distance to the line, L is horizontal distance
to the line.
Electromagnetic calculation parameters of 500kV double circuit transmission lines
Fig. 1 Dimensions of SZ1tower for 500 kV double circuit transmission lines (mm)
The vertical arrangement is one of the most common modes for 500kV double circuit
transmission lines. For this arrangement, double circuit transmission lines are located on the both
sides of the tower. In the following case, a typical SZ1 tower is taken as the model. The type of the
transmission line is 4×LGJ-630/45.Each phase has four splits with a distance of 500 mm．Four
conductors are arranged in a square shape. The rated voltage is 500 kV and the maximum voltage
could be 550 kV. The system frequency is 50 Hz. The diameter of the line is 33.60 mm and the
maximum phase spacing is 10.3 m. Fig. 1 shows the dimensions of SZ1Tower.
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Advances in Environmental Engineering
For the conductor arrangement and the SZ1tower as described above, the electromagnetic field
at a height of l.5 m from the ground level was predicted for different phase sequences and different
heights of the 500kV double circuit transmission lines.
Power frequency magnetic field distribution
Impact of the phase sequence arrangements on magnetic field
The total 18 different vertically aligned phase sequences were analyzed, six typical phase
sequence combinations of which were selected. Fig. 2 presents the magnetic field strength formed
by the six representative phase sequence combinations, which is the same of any other phase
sequences as that at one of these six phase sequences.
1
4
2
6
3
5
Fig. 2 Magnetic field strength generated by transmission lines with different phase sequences
It can be observed from Fig. 2 that, the phase sequence has significant impact on the magnetic
field strength at about 5 m away from the transmission lines. The magnetic field strength for phase
sequence 1 is 33％ higher than that of phase sequence 5. However, the magnetic field intensity in
all phase sequences is lower than the required 0.1 mT.
Impact of the line to ground distance on magnetic field
The magnetic field of the phase sequence 5, which induced the lowest magnetic field, was used
for predicting the relationship between power frequency magnetic filed intensity and the line to
ground distance, as shown in Fig. 3.
Fig. 3 Magnetic field strength generated in different line to ground distance
Advanced Materials Research Vol. 599
887
For 500kV double circuit transmission lines, when the line to ground distance is 11 m and 14 m,
the maximum magnetic field strength is 31µT and 21µT, respectively. The magnetic field strength
generated by 500kV double circuit transmission lines is less than 0.1 mT, which is the required safe
level for daily radiation. Therefore，there is no demolishing issue caused by exceeding the magnetic
field limits.
Conclusions
Under the same conditions (i.e. operating voltage, current, tower-type, and circuit parameters
including wire diameter, the number of bundled conductors and split distance), the frequency
magnetic field strength around the 500kV double circuit transmission lines are mainly affected by
the phase sequence and the line to ground distance．
1) The magnetic field strength of 500kV double circuit transmission lines are affected by the
phase sequence. The magnetic field strength for the phase sequence 1are 33％higher than that of
phase sequence 5. The magnetic field strength in all phase sequence conditions is lower than a daily
radiation limit of 0.1 mT.
2) The magnetic field strength of 500kV double circuit transmission lines is also significantly
affected by the line to ground distance. With the increase of line to ground distance, magnetic field
strength decrease significantly within a distance of 25 m from the center of the transmission lines.
For areas that are more than 25 m away from the center of the lines, the impact of the line to ground
distance is not significant. The magnetic field strength generated by 500kV double circuit
transmission lines is less than 0.1 mT, which is the required safe level for daily radiation. Therefore,
there is no demolishing issue caused by exceeding the magnetic limits.
The results show that, to reduce the frequency magnetic field strength under the transmission
lines, the most effective method is to appropriately increase the line to ground distance. However,
the increase of line height will result in the excessive increase of project cost. By a combination of
increasing the line to ground distance and optimizing the phase sequence, the magnetic field levels
can be significantly reduced. Thus, the requirements of demolishment and the corridor area could be
minimized.
References
[1]Zhenya Liu: Ultra-high voltage grid. In Chinese. Beijing: China Economic Publishing House,
2005.
[2]Xin shu Yang, Zheng cai Fu, Zhongyong Jiang et: Electric field and magnetic field of power
transmission facilities and its environmental impact. In Chinese. Beijing: China Electric Power
Press, 2007.
[3]GB15707-1995, Limits of Radio interference from AC high voltage overhead power
transmission, In Chinese. 1995．
[4] Xiong Wu, Yan sheng Ding: Status and Strategies for Electromagnetic Environment of 500 kV
Power Network in China. In Chinese. High Voltage Engineering, 2008, 34(11):2408-2411．
[5] Feng ying Wang, Wen bing Wang: The electromagnetic effect of ultrahigh voltage transmission
and transfer power engineering and its prevention methods. In Chinese. Electric Power
Environmental Protection, 2008,24(3):54-56．
Advances in Environmental Engineering
10.4028/www.scientific.net/AMR.599
Analysis on the Electromagnetic Environmental Factors of 500kV Double Circuit Transmission Line
10.4028/www.scientific.net/AMR.599.884