In the foyer of the Department of Physics at the University of Queensland in Brisbane is an experiment to illustrate, for teaching purposes, the fluidity and the very high viscosity of pitch, set up in 1927 by Professor Thomas Parnell, the first Professor of Physics there. An account is given of the experiment to illustrate the fluidity of pitch.
The motion of a charged metal particle which is itself a source of field emission has been investigated. It will be shown that the effect of electron emission from a particle may significantly affect its behaviour and may even reverse its direction of motion in the electric field within a vacuum gap. Cathode-directed particles have their energies increased by this process, while the reverse is true for anode-directed particles. These findings are in accord with the results of other investigators who have suggested that particle impact on the cathode of a vacuum gap is most likely to initiate vacuum breakdown.
Microphotography of electrode surfaces in an uncontaminated vacuum system has revealed that particles from 3 to 40 μm in diameter are removed from stainless steel, aluminium and phosphor-bronze electrodes on application of electric fields significantly below the breakdown stress. A few of these particles have been captured on Mylar film and subjected to x-ray microanalysis. The results showed that neither electrode material nor particles of polishing material were removed at the voltages used. The composition of the captured material suggests that only dust particles were being transferred across the gap, and it is believed that such particles may be instrumental in causing the sporadic or freak breakdowns sometimes observed at relatively low field strengths.
Measurements of the residual voltages of metal oxide surge arresters have been made using a variety of impulse current waveshapes. The behaviour of both metal oxide and conventional SiC non-linear resistors has been observed and compared. The appearance of "voltage spikes" at short times, ca 0.15 us, on the fronts of residual voltage records has been found and examined in the case of metal oxide arresters. The overvoltage spikes are of short duration and cannot be considered dangerous to conventional equipment insulation. However their existence suggests the need for a test, equivalent to the front-of-wave sparkover test as applied to conventional arresters.
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