Electrical Breakdown of Ice at Cryogenic Temperatures
An ice or ice-silica compound system is attractive for electrical insulation at cryogenic temperatures. A sample of ice without silica was found to have a breakdown strength of 0.3 MV/cm for ac voltages, and 0.6 MV/cm for impulse voltages. The breakdown strength of an ceicesilica compound system was 0.7 MV/cm for ac voltages. There were no visible macroscopic cracks in the sample, but microscopic cracks and voids may exist, since partial discharges were observed at about half the value of the ac breakdown voltage. The relationship between partial discharges and microscopic voids, and the voltage-time characteristics of this insulation system were studied.
Effect of electrode ice layer on prebreakdown current in liquid nitrogen
The effect of ice on dc prebreakdown events was investigated using a needle-to-plane electrode system in liquid nitrogen at 77.3 K. It was found that H/sub 2/O ice has marked effects on prebreakdown current, corona onset voltage and breakdown voltage. The breakdown voltage at atmospheric pressure depends on microscopic cracks in H/sub 2/O ice. >
D'une application pratique des indices bio-météorologiques
Abstract The purpose of the author is to determine statistically in what part of Switzerland maize could be cultivated with certain chance of rentability. The author gives first the method he used for determining the biometeorological index of four species of maize which were selected by the Swiss agronomical research stations. He has considered two possibilities for the growing period: ( a ) raising-ripening (l'approche globale); ( b ) raising-flowering, flowering-ripening (l'approche fractionee). From the biometeorological index, he calculated retrospectively the ripening time of these four species in the years 1901–1965. Assuming a priori that maize should be harvested before October 15th at the latest, he calculated, for a number of meteorological stations, the relative number of years when such conditions were fulfilled. Dividing the country in regions of similar mesoclimates and sorting these stations per region, it is possible to average the maximum altitude where maize can ripen at least 7, 8, 9 and 10 times within 10 years. Finally, taking into account the exposure and ground slope, he draws maps of the theoretically possible extension area, which maps are more reliable and detailed than the ones derived from actual means.