Search

It is well known that after current interruptions, a fine Cu-Cr melted layer is formed on the electrode surface, and the vacuum insulation between electrodes is improved. However, the influence of the depth of the arc-melted layer on the vacuum insulation is still not clear. The objective of this paper is to determine the influence of the depth of the arc-melted layer of the cathode on the vacuum insulation. A 12 kV vacuum interrupter with a pair of rod-plane electrodes was designed. A DC current source was applied to the vacuum interrupter, and the rod electrode was chosen as the anode. A drawn vacuum arc in the anode spot mode was used to generate melted layers with different depths on the rod electrode. The arcing time was controlled to 0, 10, 46 or 73 ms. Then, the vacuum gap was adjusted to 1 mm to measure the basic lightning impulse breakdown voltage. Standard positive-polarity 1.2/50 μs lightning impulses were applied by a basic up-down method, in which the rod electrode was the cathode. Experimental results revealed that the breakdown probability followed a Weibull distribution when the breakdown voltage reached saturation. The 50% breakdown voltage U50 with arcing times of 0, 10, 46 and 73 ms was 55.6, 73.3, 75.5 and 77.9 kV, respectively. Next, a cross section of the rod electrode was analyzed using an electron microscope, and the average depths of the arc-melted layers were 0, 5, 35 and 65 μm at current arcing times of 0, 10, 46 and 73 ms, respectively. The depth of the arc-melted layer varied approximately linearly with the arcing time. The U50 values of the vacuum gaps with the arc-melted layers were significantly larger than that without a melted layer but very close to each other for all arc-melted layer depths. Thus, the melted layer did improve the breakdown voltage, but the depth of the arc-melted layer had little influence on the breakdown voltage. [ABSTRACT FROM AUTHOR]

Inverted polarity effect was studied at the breakdown of point-to-plane discharge gap filled with air at a pressure range of 0.013–0.3 MPa. High-voltage nanosecond pulses were applied to the electrode with a small radius of curvature. Pulser was operated at both negative and positive polarities in the single-pulse mode. Waveforms of voltage pulse, discharge current, and intensity of the discharge plasma radiation near the electrode with a small radius of curvature were registered. It was obtained that at the breakdown of point-to-plane discharge gap filled with air, the breakdown voltage at positive polarity of the pointed electrode was higher than that at negative one. The inverted polarity effect was shown to come to naught with an increasing of air pressure up to 0.3 MPa. It is suggested that the inverted polarity effect is related to the impeded formation of the explosive emission centers on the flat electrode (cathode) after arrival of the ionization wave front to the one. In addition, both the inverted and the ordinary polarity effects were not observed at the breakdown of nitrogen at pressures of 0.4 and 0.7 MPa. [ABSTRACT FROM PUBLISHER]

The authors introduced a concept of self-sensing neutralization system by means of automatically ejected charged particles from alternative current microhollow cathode discharge. When the positive bias was applied to the third electrode, a real current flow was only detected during negative polarity period of voltage applied to the first electrode. On the other hand, in the case of negative bias, there was only the real current during positive polarity period. These results mean that our system shows simultaneously the self-sensing and then neutralizing characteristics in a period. [ABSTRACT FROM AUTHOR]

The nanosecond single-pulse voltage was employed here to generate a large-volume discharge between the wire-plane electrodes in nitrogen. In order to find out the effect of pulse polarity on the propagation of a large-volume discharge, both the positive and negative pulses were applied to the wire-plane electrodes, respectively. Images presented here reveal that the discharge channels are more homogeneous under the negative pulse, and the propagation speed of the discharge channels is faster under the positive pulse. [ABSTRACT FROM AUTHOR]