The measuring system we used consisted of two UHF sensors with a frequency band of 400 MHZ～1500MHz and a digital oscilloscope with maximum 2 GS/s digital rate in its two channels. The difference in arrival times of UHF signals at two sensors can be measured to assist with locating defects in GIS. The test results in the laboratory indicate that the fault location precision depends on the digital rate of the oscilloscope. In actual site test, if the sample rate is low, it is could not have enough sample plots to recover the real pulse wavefronts, which is difficult to identify the arrival times at the two sensors by the first peak of UHF waveform. In this paper, a new algorithm has been described, which applies cubic spline interpolation to increase points between two real sample points, and improve the location precision of time flight method. And then the distance difference between two waves can be determined by using cross-correlation function. In addition, the application software has been developed to help locate PD source in GIS.

This paper presented some new experimental results observed in our investigation. Based on the experiments, it was found that the different voltage application sequence on the test samples could influence the flashover voltage of the tested samples. Three kinds of voltage application sequences were compared and three kinds of Alumina samples were involved in this paper. In general, the flashover voltage is the lowest if the applied voltage started from a lower voltage (-2kV) at a -2kV step; the flashover voltage could be the highest if the applied voltage started from -22kV. The surface charge distributions were observed after the voltage was applied. According to the experimental results, the change of the flashover voltage of the test samples could be attributed to the state of surface charge distribution with different voltage application sequence.

This paper reports on the infuence of sintering conditions on the flashover/preflashover characteristics of alumina insulators in vacuum under an impulse voltage. Four kinds of alumina insulator were studied, which were prepared using the same formula with different sintering conditions. The surface pre-flashover and flashover phenomena of different samples in vacuum have been observed under impulse voltage. Based on the experimental results, the characteristics of pre-flashover and flashover vary with different kinds of test samples. It was found that the insulators with a higher sintering temperature had a lower flashover voltage, and more active pre-flashover. From a scanning electron microscope (SEM) analysis of alumina insulators, we conclude that the methods of preparing alumina samples can affect their microstructure resulting in a change in the pre-flashover and flashover performance as alumina insulators.

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.

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.