| The electromagnetic environment of 220kV power transmission and distribution project includes the power frequency electric and magnetic field and radio frequency interference. Since the voltage level of 220kV is not too high, the electric field intensity of the line surface is still very low. As a result the problem of radio frequency interference is relatively insignificant. However the problem of the power frequency electric and magnetic field attract people's attention as more and more 220kV power transmission and distribution projects are built in urban areas. Research in this area can by tracked in many foreign and domestic studies. And most of the current designs are complied with the national and international standard on electromagnetic environment. But due to the complexity of the conditions of the substations and transmission lines, the studies on specific cases are not enough to get a general understanding of the overall situation of the electromagnetic field environment in different places. This paper focused on the evaluation of the magnetic field of the typical design issued by the State Grid for the power transmission and distribution projects, which can be help to understand the general electromagnetic environment conditions and further improve the design for the substations and transmission lines.This paper presented the numerical method in calculating the power frequency magnetic field of typically designed 220kV transmission lines and substations. Based on the Biot-Savart Law, the magnetic field at any location generated by any line can be calculated. Then using superposition theorem, magnetic field distribution generated by all the equipments can also be figured out. By analyzing different magnetic sources in substations, is was concluded that the primary magnetic sources that determine the overall magnetic field level in and out of a substation were conductors with high current, i.e. the high voltage lines, the bus bars and the lines connected to the transformers. The influence of operation modes on the distribution of magnetic field was discussed also. The magnetic field of transmission lines is related to many factors including the number of loops it carried, the height of the tower, the distance between the lines and the ground, the layout of the three phases, the phase order of the multi-loop transmission lines and the distance between phases.Finally according to evaluation of the power frequency magnetic field of the typically designed 220kV transmission lines and substations, some measures to reduce the magnetic field were proposed, which can be a reference in further design. On the other hand it also provided some valuable information for the protection of the electromagnetic environment around the power transmission and distribution facilities. |
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