Justin Martin

An oil peaking switch to drive a dipole antenna for wideband applications

When the load is an antenna, the High Pulsed Power (HPP) generators allow generating electromagnetic waves in the form of pulses for wideband or ultra wideband applications. In this case, the HPP generator is usually made up of a primary energy source loading a power-amplification system. A Marx generator or a Tesla transformer is classically used as a power-amplifier. Our structure uses an innovating very compact resonant transformer. This power amplification device is connected to a fast switch which forwards the energy from this source to the antenna. The antenna behavior is directly linked to the performances of the main element of this whole device: an oil peaking switch.

A new formula for predicting the amplitude of the dynamic pressure wave resulting from breakdown in water gap

The study is part of a global research program concerning the development of an alternative electrical stimulation technique for conventional hydraulic fracturing in tight gas reservoirs. More precisely, the goal of this work is to predict the shock wave amplitude induced by an electrical breakdown in water. The influence of the gap length enhancement on the peak pressure improvement will be shown, and the major importance of improving the electrical circuit maximum current will be demonstrated and accompanied by the development of a new empirical formula directly relating to maximum pressure and maximum current. Furthermore, we point out the fact that the frequency spectrum of the shock wave depends from the speed of current injection into the water gap. These results will allow the optimization of the electric fracturing technique by increasing the electro-acoustic yield.

Influence of hydrostatic pressure and temperature on the water dielectric strength and on the dynamic pressure wave

The paper presents experimental results for breakdown voltage in water gaps as a function of water hydrostatic pressure and temperature. Low applied electric field and high switching energy ensure the development of subsonic electrical discharges. For these discharges, the vapour bubbles involved during the pre-breakdown phase are initiated by joule heating effect. The dependencies of the U50 breakdown voltage on hydrostatic pressure up to 5MPa and on the temperature up to 90°C are investigated. The pre-breakdown phase of the discharge is characterised by the different power consumption behaviours and by the energy losses according to hydrostatic pressure and temperature. A minimum threshold value of the discharge energy losses can be highlighted. Experimental measurements concerning the shock wave generated by the subsonic discharges are presented. Results point out that the dynamic wave is not dependent from the hydrostatic pressure. On the other hand, for a constant energy at breakdown time, the dynamic pressure wave increases with the temperature. These results will allow the optimization of the electrical energy ratio converted into acoustic energy.

Corona discharges experiments in water and transition to subsonic discharges

This paper discusses the influence of the discharge current on the compressive shock waves generated by supersonic and subsonic discharges in water gap. The two different ways leading to dielectric breakdown in a water gap will be investigated. The transition phase between the two breakdown modes depends on the electric field and the electrical energy switched. The shock waves associated to breakdowns in water gap will be studied. Whatever the water breakdown mode will be, the peak pressure linearly depends from the peak current. For a constant peak current, the peak pressure value increases with increasing gap length. Moreover, the electro-acoustic efficiency is better using a supersonic discharge.