Chen Shuiming

Influence of grain size on distribution of temperature and thermal stress in ZnO varistor ceramics

The nonuniformity of temperature distribution within ZnO varistor ceramics would decrease its energy absorption capability. In this paper, the distributions of current, temperature and thermal stress within the microstructures of ZnO varistor ceramics are simulated using Voronoi diagram models. The results show that the current concentrates through a few paths in ZnO varistor due to the nonuniformity of ZnO grain size and the variety of electrical characteristics of grain boundaries, which induces local high temperature and great thermal stress when injecting impulse current into ZnO varistor, and leads to melting puncture or cracking failure. The influence of the ZnO grain size on the distributions of temperature and thermal stress within ZnO varistor ceramics is analyzed in detail. The energy absorption capability of ZnO varistor ceramics can be greatly improved by increasing the uniformity of ZnO grain size or decreasing the average size of ZnO grains.

Impulse characteristics of grounding systems of transmission-line towers in the regions with high soil resistivity

The lightning protection effects of power transmission lines are related to the impulse characteristics of grounding systems of transmission-line towers. The influences of several main factors on impulse grounding properties are systematically analyzed by simulation experiments according to the simulation theory in this study. Soil resistivity was changed in the region between 100 to 5103 /spl Omega//spl middot/m. The influential regularities of different parameters on impulse grounding resistance and impulse coefficient of different grounding devices for transmission lines in high resistivity region are discussed. By analyzing the experimental results, the authors conclude that the structure of grounding systems should be selected according to soil resistivity, geological structure and technical economy analysis. The fitting calculating formulae of impulse coefficients and power frequency grounding resistances of different grounding systems are acquired. The simulation results are in good agreement with those of field experiments in the literature.

Equivalent simplified parallel multi-conductors model of shielded control cable in substation

The electromagnetic coupling between the control cable with metal shielding sheath and metal conductor of grounding grids in the substation of a power system threatens the safe operation of an electronic system connected with the control cable. In order to simplifying the electromagnetic coupling analysis of this system, the core-sheath model of a control cable is replaced by a parallel multi-conductor model with theoretical analysis and numerical computation in this paper. From analysis of the resistance and the self-inductance of the sheath, the mutual inductance and the capacitance between the core and the sheath in both models, four nonlinear equations to solve the four unknown parameters in the parallel multi-conductors model are established. A program has also been coded to solve the equations. The results of the parallel multi-conductors model are compared with the analyzed ones of the actual control cable by the PSCAD software package. They have good agreement with each other.

Lightning electromagnetic environment assessment of software park near transmission lines

The lightning electromagnetic environments of planned Zhongguancun Software Park near transmission lines, including electrical field, magnetic field and grounding potential rise, are assessed by numerical analysis. From this analysis, we can conclude that the lightning strike is a serious threaten to the software park, protective countermeasures should be adopted to improve the electromagnetic environments of the software park.

Power frequency electromagnetic environment evaluation of Zhongguancun Software Park near transmission lines

The power frequency electromagnetic environments of Zhongguancun Software Park near planned high voltage transmission lines, including electrical field and magnetic field, are evaluated with CDEGS software in this paper. From this analysis, we can conclude that the power frequency electromagnetic environments of the Software Park are below the maximum ecological allowed exposure values for the general public given by HJ/T 24-1998. Nevertheless, the power frequency magnetic field may interfere with the sensitive computer display unit.