Study on the measurement of reducing electric field intensity under UHV transmission lines

The tower height of UHV transmission line has to be decreased in some special circumscription. The electric field intensity at ground level will increase when the decrease of conductor height, even exceed the standards limit. Therefore, the 'special tower' must be introduced to control the electric field intensity at ground level, which can be effectively decreased by using shielding wires. The optimal plan of shielding wires arrangement is recommended in this paper. The main measurement to control the electric field intensity at ground level under a transmission line is to increase the height of conductors. But in some special circumscription, when the conductor must keep small height, the electric field intensity at ground level might exceed the national standards. Therefore, study on the optimization of electric field intensity such as using shielding wires is an urgent problem to be solved in an UHV project. The electric field intensities at ground level with the different arrangement of shielding wires are calculated in this paper, the optimal plan of shielding wires arrangement is proposed by contrasting the calculation result. From the paper the conclusions are as follows: 1) Using shielding wires to reduce the power frequency electric field intensity under a UHV transmission line is proposed in this paper, and the configurations of shielding wires are discussed. 2) It is possible to reduce the power frequency electric field intensity by using overhead shielding wires or setting earthed rail on the flat roof under different conditions. The test results introduced in this paper indicate that the electric field intensity can be reduced by 35% by using shielding wires and the electric field intensity can be reduced by 30%-73% by using earthed rail.