The “Energy” Series Generators with Output Power from 2 to 200 kW for Electromagnetic Soundings with the Use of Power Transmission Lines

One of electromagnetic (EM) sounding techniques for investigating the distribution of electrical conductivity with depth to determine the geological structure of the Earth's interior is a controlled-source method (CSEM). The depth of investigation and a source-receiver separation for CSEM sounding with a horizontal electric dipole source are dependent on its length and on the value of current through it. From this point of view, a-grounded at the ends overhead power transmission line (OHL) can be successfully used for deep CSEM soundings. Since, zero-sequence impedance value of an OHL in a frequency range from 0.01 to 10 Hz is small, e.g. a few ohms for more than a hundred kilometers long OHL, then a current source, i.e. a transmitter, of sufficient power is able to provide the amplitude of the current through an OHL of several hundred amperes. Therefore, the use of an OHL for deep CSEM soundings allows to increase a transmitter-receiver separation up to 1000 km and to reach a depth of investigation of 80-100 km. CSEM soundings effectiveness is influenced by a transmitter's design and characteristics. Main requirements for the design of transmitters for deep CSEM soundings by using an OHL were discussed. The transmitters of 200, 30 and 2 kW power were developed. The ability to generate an arbitrary waveform, with controlled amplitude, shape, and frequency, is a main distinctive feature of the transmitters. The transmitters were used for deep CSEM soundings with OHLs in a number of experiments that took place on the Kola Peninsula and in Western Siberia.