| High voltage ceramic capacitors are widely used in the field of power system due to their characteristics of small size, high capacity, long life time and good stability. While the BaTiO3 categorized sintered ceramic were usually used as the dielectric in the high voltage ceramic capacitor. The sintered ceramic capacitors usually had characteristics of low dielectric breakdown strength, large partial discharge capacities and bad temperature stability, because there are remained pores in the ceramic after the sintered process, as well as Curie temperature was close to room temperature. The development of the high voltage system has more critical requirement on cries, especially that the capacitor is requested to have a higher breakdown strength, temperature stability and low partial discharge. The traditional ceramic capacitor could not match with the development of high voltage system.Niobate glass ceramic could get both high dielectric constant and high breakdown voltage through controlled crystallization method, the structure of which is of no pore. There are many researches and studies on the system of niobate glass ceramic materials, however there were little report concerning on how to transform this new material studies into an applicable capacitor device. This paper aimed at making the niobate glass ceramic to a high voltage capacitor through the study of the material, electrode and packaging, and this paper solves the problems of high partial discharge and bad temperature stability on traditional ceramic capacitor, by advanced developing the niobate glass ceramic into a high voltage capacitor in super high voltage power system.This paper studies the relation in between of the crystallization, microstructure. and the dielectric performance of ANb2O6-NaNbO3-SiO2 system first. In the PSNNS system A means Pb1-xSrx, in the PBNNS system A means Pb1-yBay, while in the PSNNS system A means Ba1-zSrz. In the study of controlled crystallization of the PSNNS, PBNNS and BSNNS system of glass ceramic, it was found that with the increase of crystallization temperature, there were two exothermic peaks. The X-ray diffraction revealed that the crystal phase at lower temperature was pyrochlore structure phase, and the high temperature phase were NaNbO3 and (Pb/Ba/Sr) Nb2O6. In the process of study on the structure and performance it was found that with the increase of crystal temperature,the grain size improved, and the dielectric constant, dielectric loss also increased, while the temperature stability and voltage stability had decreased. And then the glass phase design was first proposed to optimize the glass ceramic performance for the practical use. By adding proper content of Pb2+, both the dielectric constant and dielectric breakdown strength can be improved. And the dielectric loss can be decreased to 0.0078 by adding Al3+, and the dielectric loss can be reduced to 0.0028 by adding Gd3+, the dielectric constant number of which remained unchanged.The PSNNS system glass ceramic was chosen as the dielectric material to study the electrode and compacting, and the size was 20 mm in diameter,1 mm in thick. It was found that the screen printing electrode used in industrial had many pores between the electrode and dielectric interface, leading to large partial discharge capacity and low breakdown voltage. The direct current (DC) breakdown voltage of the printing electrode of the capacitor was 50.0kV. and the alternating current (AC) breakdown voltage was 4.0kV. The starting partial discharge voltage was 1.7kV. and the partial discharge capacity reached at 26.4pC at 3.0kV. To eliminate the pores in the interfaces, the active brazing method was used to make the electrode, and the porosities in the interface were eliminated, but the dielectric was deoxidation under high temperature with high vacuum environment. The magnetic sputtering deposition was used to make electrode, the interface was pore free and it had smooth edge. However the film electrode had low conduction ability that was easily burned out under high current. Then the magnetron sputtering/tin-lead solder electrode was made to improve the conduction ability, the DC breakdown voltage improved to be 60.0kV, and the AC breakdown voltage improved to be 4.8kV. And the starting partial discharge was improved from 1.7kV to 2.8kV, and the partial discharge capacity was decreased to 6.36pC at 3.0kV. In the simulation study it was found that the decrease of electrode edge and the increase of electrode thickness can reduce the electric field distortion coefficient, which can improve the dielectric breakdown strength.On the packaging material research, sever kinds of epoxy resin were firstly studied to find out the proper one. Future researchers found that the electric field serious distorted at the three phase boundary, and the simulation and experiment presented that worst aberration of electric field happened on the edge of the three phases. In order to even the aberrant electric fields, this paper was prior to import dielectric packing technology. By improving the dielectric constant of epoxy resin while keeping other performance unchanged, the DC breakdown voltage was improved from 50.0kV to 75.0kV, while the AC breakdown voltage increased from 4.0kV to 7.5kV respective. In the meanwhile, the nonlinear resistivity materials was used to homogenize the electric field, and the DC breakdown voltage was improved to be 78.0kV and AC breakdown voltage increased to be 8.5kV.At last, this paper designed a niobate glass ceramic capacitor used in high power system. And its performance was studied in practice use. The capacity, dielectric loss, partial discharge, temperature stability, voltage stability, lightning impulse as well as repeated charge and discharge performance was studied. And the results showed that the performance of the new capacitor was better than the regular sintered ceramic capacitor. |
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