On Breakdown Of Rocks By Electric Pulsed Power

Breakdown of rocks is an activity associated closely with humanity. There are many ways to do so. Conventional methods include physical disruption(such as mechanical crushing) and chemical methods(such as explosive blasting), which have several drawbacks such as environment pollution and low efficiency. New destruction methods with higher efficiency and more environment-friendly techniques are badly needed.Pulsed power technology is one of the new means. It gradually developed based on military demands from 1960 s. The technique focuses on how to store energy in a relatively long time and release them in an extremely short time, and thus we can get a high instantaneous power, namely pulsed power. The research of this dissertation is conducted based on the pulsed power technology. The method can generate a high voltage and steep pulse, which will help to form plasma channels in the inner rocks, and rocks break down while the channels expand with much energy penetrate into the channels. It is a clean,controlled and safe scheme, which has a certain practicality.First,both conventional and electrical pulse methods are introduced, and then the structure(Marx generator) of the crushing device is given. What is more, some specific parameters including its resistance, stray inductance, stray capacitance are calculated and assembly units are selected accordingly. Then two key techniques of the devices- switches and trigger system are analyzed in detail. Meanwhile, detailed schematic diagrams are given.In order to obtain such pulsed power, a high-performance switch is badly needed. The inductance, ablation and other factors of the switch should be taken into account. And hence, materials and electrode distance should be chosen suitably. The design of shield structure is also given in order to reduce the impact of metal spatter on the inner wall of the switch when discharging, because metal spatter will cause insulation resistance decreased of the switch.Trigger is another crucial factor of a Marx generator. To isolate high voltage, optic fiber isolation, i. e. electricity- light, light- electricity conversion,is utilized in the design of the trigger system. In the same time, a combination of capacitor and resistor is used toplay a role in isolation. In addition, pulsed transformer is also a kind of isolation, for which there is not direct electrical connection between the primary coil and the secondary coil. What is more, the life of the trigger system as well as the capacitors are tested, which is proved to perform well enough with more than one hundred thousand times in experiments.Then,a practical experimental platform was set up to carry out our program. The results show that this equipment can safely accomplish the task of breaking down the rocks. Usually, the rocks and the electrodes are immersed in a kind of liquid such as water or transformer oil, in order to reduce surface flashover and increase the discharge in the inner of the rocks, which will lead an easier destruction. Water is often used as the insulating liquid because it is more economical than other resources and abundant in reserves. What is more important, it does not pollute the environment while other insulating liquids such as transformer oil, is expensive, and if there is a leak, the soil will be contaminated. Also, the oil is unlikely to degrade in the short term.There are limitations in this electrical pulses method of breaking down rocks. For example, when breaking down large rocks, it needs higher voltage and higher energy in a larger Marx generator, which requires large-scale capacitors, and brings difficulties to trigger synchronization. In addition, it will be very convenient if we can discharge with the rocks and electrodes exposed directly in the air without isolating fluid, which will in turn saves water significantly. These problems need more further research.