大地电磁勘探中的电力线工频干扰

THE POWERLINE INTERFERENCE IN THE MAGNETO-ELECTROTELLURIC EXPLORATION

大地电磁法勘探中,因电力线频率不单一,产生的工频干扰场量级大,给数据处理造成困难。为给削弱、压制干扰提供依据,进行了试验。在地表上方某一高度无限长直导线模拟输电线,推导、计算在其通以谐变电流时的电磁场值。计算结果表明:即使距离输电线500 m处,其干扰场依然可以完全淹没目标信号;但该干扰场有固有特性和规律。通过探讨得出,在一个波长之外,电力线产生的电磁场为平面波转而成为有用信号,在一个波长之内,可以根据其电、磁场的方向性有选择地布极,以避免两个方向的视电阻率同时受到干扰。

Because the power frequency is complex and will produce heavy electromagnetic noise in magnetotelluric sounding, the dis- tortion of electromagnetic signal and the troubles in data processing and interpretation may occur under the condition of serious disturb- ance. In order to provide reference for weakening and suppressing the interference, the authors set the line current source above the ground level to simulate the power lines, inferred the formula and calculated the electromagnetic field. The results show that, even if the transmission distance is 500 m, the disruption field can still completely submerge target signals. However, this interference field has its fixed features, so the following conclusions can be drawn through the calculation and discussion of these features： On the one hand, the electromagnetic field generated by power lines is a plane wave which can be converted into useful signal outside a wave- length ; On the other hand, within the wavelength, the situation that apparent resistivity in both directions encounters interference at the same time can be avoided by arranging the electrodes according to the direction of the electric field and magnetic field.