Based on the experimental results--the trap distribution characteristic and flashover performance of Alumina ceramic samples in vacuum which were prepared by different ways, this paper try to discuss the relationship between the trap distribution and the flashover performance of Alumina ceramic sample. Comparing with the flashover performance of the insulator sam-pies in vacuum, it was found that the trap distribution could influence on the flashover performance. Based on our investigations, the relationship between the trap distribution and the flashover performance was discussed. It seems that the trap distribution maybe, the better parameter to reflect the flashover performance, and the further more works are needed to set up the relationship between the trap and the flashover.

This paper has investigated the thermally stimulated current (TSC) of Alumina ceramics using a uniform electrode system. Experimental results with different Alumina ceramics showed that TSC characteristics of the samples prepared with varied metal oxide additives was different. The trap distribution parameters were calculated from TSC curves, the calculation results show that the additives significantly influence the trap distribution.

In this study, the surface charge distribution on insulators in vacuum has been investigated under an impulse voltage (0.7/4μS) with a non-uniform field electrode system. The insulators studied were 99.9% alumina specimens with the shape of right circular cylinders about 5mm thick and 20mm in diameter. Using an electrostatic probe with shield in the form of capacitive voltage divider that was connected to an electrometer, the surface charge distribution on insulators were measured. The applied impulse voltage, and the corresponding current waveforms, the signal of luminosity were also observed during the voltage application. We investigated the surface charge distributions at different impulse voltage levels, at different shot number with a same voltage level, at the situations after a flashover occurred. Based on the experimental results, we found that the surface charge density on insulators is increased with the increase of the applied voltage, the shot number has a little influence at the same voltage level, and the charge density is decreased a lot after a flashover occurs. It's also found that the increase of charge density is often accompanied by the preflashover events.

This paper provides some experimental investigation on the influence of the surface roughness on the flashover performance of ceramics in vacuum. The test samples were prepared with four kinds of ceramics (99.9% Alumina) which were polished by four different SIC abrasives. The flashover performances of 20 kinds of test samples have been tested with an impulse voltage in vacuum. According to the experimental results, it was found that the roughness of the test sample was quite different among different ceramics although the same grinding procedure was used with the same abrasive. It was also found that the flashover performance was influenced by the surface roughness, and there is a trend that the samples with a lower surface roughness have a higher breakdown voltage.

The interference voltage in the secondary cables through high voltage bus, current transformer and capacitance coupling voltage transformer caused by lightning striking the region of transmission line neighboring substation were analyzed EMTP software package is used to calculate this problem. The equivalent models of different equipments, especially the transient models of current transformer (CT) and capacitance coupling voltage transformer (CCVT), were discussed The analysis results stated that the interference voltage in file secondary cables caused by lightning striking the region of transmission line neighboring substation is serious, which must be paid attention to by electrical engineers.