The fact that the dielectric strength of liquids is higher than that is for dielectric solids at the times of voltage duration less than lps was founded at Tomsk Polytechnic University at the end of the fiftieth. Fig.1 illustrates the dependence of the breakdown voltage Uw to the time of voltage acts t~ (time of voltage increasing till the coupon breakdown) for several materials. It can be of transformer oil and tap water is higher than that is for quartz, marble and sandstone to the left of volt-time characteristics crossing.
The possibilities of electropulse destruction of nonconductive materials and boring at various laboratory and field conditions have been studied at Tomsk Polytechnic University during many years. This work is devoted to determining the possibilities of water use to demolish granite and concrete at large distance between the electrodes. It was found that the breakdown voltage during the pulse drop is 1.5-2.0 times less than that for the case when the discharge happens during the pulse rise. Consequently, we have less voltage amplitude and current leakage in water. The possibilities and the efficiency of the electropulse destruction of rock and concrete in water are discussed.Words: breakdown voltage, interelectrode distance, material destruction, granite, pulse efficiency, specific energy. IntroductionElectric pulse technology of rock drilling and demolition is based on the fact that at a very short voltage pulse the breakdown inside the solid dielectric occurs faster than the surface flashover between the electrodes. This fact was discovered in early sixties by Vorobiev [l]. The experimental and theoretical studies on the applications of this effect were summarized in [2] for the time period of over 30 years. It was shown that the most of the solid dielectrics could be broken down in the insulating liquids like transformer oil and diesel &el and even in water.Recently, the main issue in the electric discharge drilling technology has been how to make it ecologically clean. Instead of mineral or organic oils, technical water is used as a liquid dielectric. Diesel &el and transformer oil are good as insulation liquids, but cause ecological problems. The usage of water as an insulation liquid have not shown good results, because water has less breakdown voltage and provides considerable current leakage.The objective of our investigation is to determine effective conditions of material destruction due to the discharge channel in water. The following characteristics are important for the electropulse technology of material destruction and boring: amplitude of applied voltage U,, time of
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