Research Of The Mechanism And Characteristics In Air Discharge Based On The Fluid-Chemical Reaction Hybrid Model

To satisfy the increasing demand on the power electricity in China, more and moreultra-high-voltage (UHV) transmission lines will be built in next five years. With theincrease of the voltage rating, many new problems arise, including the corona discharge,insulation and manufacture of UHV electrical equipment. To solve the problem in UHVpower transmission engineering, Chinese Ministry of Science and Technologysupplemented an extra973project regarding the electromagnetic environment andinsulation of UHV transmission line in2011, which aimed at solving the newengineering problem arising in the UHV power transmission engineering and finallypromote the safety operation of UHV transmission line.The corona generated on UHV transmission line is a kind of air discharge. Thephysical mechanism of air discharge research is interdisciplinary. At present, it is verydifficult to diagnose the progress of air discharge by laboratory test due to the restrictionof the probe techniques. Therefore, with the limited test results, to study air dischargemechanism by the numerical simulation method can not only save high cost, but alsocan control and optimize the process of air discharge. The achievement in the study onmechanism of corona discharge can offer theatrical tools for the outer insulation designof UHV electrical equipment.At present, most research of air discharge just utilized a single theory and model ofair discharge microscopic physical process. It is short of comprehensive considerationof chemical reaction process in air discharge process. Therefore, this paper establishedmixed numerical air discharge model based on fluid-chemical reaction hybrid model tostudy microscopic physical process and characteristics. The characteristics of physicalprocess which can describe the air discharge microscopic progress are proposed. Themain influence factors (pressure, discharge gap, and discharge voltage) to the process ofair discharge are analyzed. At the same time, an atmospheric pressure corona dischargeobservation system was also set up to analyze the progress properties of air discharge.The measured corona discharge current and current waveform are helpful to validateand improve the numerical model. The results of the research provided theory andnumerical method for high voltage transmission line corona discharge. The maincontents and achievements of the paper are as follows:1) According to the insufficient of transport parameters in air discharge numerical model, a one-dimension model is established. The electron energy distribution functionis obtained by solving two Boltzman equations. Then, the transport parameters such aselectron mobility, diffusion coefficient are gained.2) A hybrid model of air discharge based on fluid-chemical reaction is establishedand the governing equation, boundary condition and computing method of initial valueare deduced. Based on the hybrid model proposed in this paper, a variety of physicalstructure discharge under low pressure is simulated. Compared with experimentalresults of related literatures, the hybrid model adopts12kinds of particles and27kindsof chemical reaction to reflect the basic process of air discharge. Then, the basicdynamic progress of air discharge under low pressure, the microscopic characteristics ofphysical progress and the characteristic features of air discharge changed with pressureare discussed.3) In this paper, the photoionization is introduced into the fluid-chemical reactionhybrid model and the microscopic physics process of air discharge under atmosphericpressure which can be used in UHV transmission line is studied. In addition, thecharacteristics of physical process in atmospheric pressure air discharge are analyzed.The results indicate that the particle density, electron temperature, and the distributionsof electric field and energy are the most important feature in the process of air dischargewhich change with the microscopic processes of air discharge and is closely related totransmission line corona discharge onset, self-sustained and dissipation process andluminescence phenomenon.4) The high altitude air pressure, the discharge gap, discharge voltage are the mainfactors influence the air discharge characteristics, calculation were also conductedreveal the specific influence of external factors on the air discharge microscopicphysical processes. And the results show that the high altitude pressure influences themacroscopic properties of air discharge by changing the electron mean free path andelectron drift. The discharge voltage and discharge gap will bring a rapid change of theelectric field distribution and thus influence the development process of air discharge.5) Verifying tests under atmospheric pressure have been carried out using abar-plate electrode air discharge observation measurement system. The air dischargefrom the onset to stable development process through corona image and ultravioletphotons were observed and analyzed by UV camera respectively. The fluid-chemicalreaction hybrid model was validity by the comparison of discharge voltage-currentcharacteristics and discharge current waveform.