Investigations have been carried out on Alumina insulators in vacuum under an impulse voltage (0.7/4μS) in order to study the relationship between surface charging and surface preflashover phenomena of insulators in this paper. The Alumina insulators studied were 99.9% alumina cylindrical specimens and the employed electrode system is a non-uniform field electrode system. The surface preflashover phenomena were observed and the surface charge distribution of insulators was measured under varied impulse voltage levels and different shot number at a same fixed voltage level. Based on the experiments, it was found that the charge density and distribution is not only dependent upon the magnitude of the impulse voltage, but also the preflashover phenomena. The number of voltage shot has little influence on the charge density and distribution at the same voltage level if the surface preflashover phenomena can be observed during voltage shot.

In this paper, creeping discharge of oil-polypropylene insulating system have been studied using an experimental model with the flowing oil under ac voltage. The ac creeping discharge inception voltage of the oil-polypropylene system has been tested under varied conditions. According to the experimental results, all of the oil temperature, the oil flow rate and the position of poly propylene film can influence the ac creeping discharge inception voltage of oil-polypropylene system. The ac inception voltage of this system is increased along with the increase of oil temperature and oil flow rate. Moreover, the ac inception voltage is higher at the position near to oil entrance than that at the position far to oil entrance. Considering the experimental results, a new composite insulating system is put forward for reducing the negative effects of streaming electrification in larger power devices with forced-oil cooling systems.

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.

A new set of facility for accelerated aging test of composite insulators has been developed at CEPRI (China Electric Power Research Institute). This paper mainly described the measurement and parameters monitoring system of this facility. This system can monitor total six channels current of insulator in real time, and it can also collect the corresponding information at the same time, such as the applied voltage, the environment parameters. Based on the collected data, the system can analyze and statistic the characteristics of the aged leakage current in time, and it can also save the important test data during the whole test procedure. In addition, this system has the capability of auto alarm, auto reset for the unexpected accidents during the test procedure. This system is a powerful system for the research on the aging performance of composite insulator.

A measuring system for on-line detecting partial discharge of generators has been designed with the ultra high frequency (UHF) and high frequency (HF) method. It not only has the capability of calibrating the PD level, but also has the excellent ability of anti-interfering on site. The test data shows this technique is very promising.