Effect of Vacuum on the Dielectric Strength of the Medium in ESG Gaps
Abstract Generated abstract
This paper examines how vacuum level affects dielectric strength and breakdown behavior in the gaps of an electrostatic generator intended for high-vacuum operation, motivated by the limitations of compressed-gas generator enclosures and the needs of spacecraft power sources. Using an experimental generator design without rotating parts, the authors compare load characteristics at atmospheric pressure and at several vacuum levels against a calculated characteristic. The tests show a sharp reduction in dielectric strength near 10^-1 mm Hg, approximate equivalence to air near 10^-3 mm Hg, partial suppression of breakdowns near 10^-4 mm Hg, and near-complete elimination of breakdowns with agreement to the calculated characteristic near 10^-6 mm Hg. The results suggest that the proposed generator can operate satisfactorily in high vacuum, while also confirming instability in vacuum breakdown voltages.
Full Text
EFFECT OF VACUUM ON THE DIELECTRIC STRENGTH OF THE MEDIUM IN ESG GAPS
A. P. Kononov, V. A. Lukutin, L. M. Leus, A. I. Naletov
(Presented by the scientific seminar of the Department of Theoretical Foundations of Electrical Engineering and by the ESG Department of the Scientific Research Institute of Nuclear Physics)
All existing electrostatic generators with an output voltage on the order of hundreds of kilovolts operate in a compressed-gas medium in a special cylinder. In this cylinder, in order to increase the dielectric strength of the medium, a pressure is created, the magnitude of which sometimes reaches 30 atmospheres. But the high pressure created in the closed volume where the generator and motor are located exerts a strong resistance on the rotating parts of the electrostatic generator.
This resistance leads both to overheating of the entire installation and to a decrease in the efficiency of the generator. Despite the fact that at present ESGs operating under pressure have already proved themselves favorably, the advent of spacecraft requires reliable energy sources operating in a deep vacuum.
Fig. 1. 1 — at atmospheric pressure; 2 — in a vacuum of \(1 \cdot 10^{-4}\) mm Hg; 3 — in a vacuum of \(1 \cdot 10^{-6}\) mm Hg; 4 — calculated.
For this purpose, a design of an electrostatic generator for operation in high vacuum was developed. The absence of rotating parts in the proposed generator made it possible to eliminate bearing lubrication and heating of rubbing parts. A detailed description of the design of the experimental generator is given in [1]. The experimental load characteristics are shown in Fig. 1. These characteristics are presented for one and the same excitation voltage, but for different vacuum levels. Curve 1 is for air, curve 2 for a vacuum of the order of \(1 \cdot 10^{-4}\) mm Hg, curve 3 for a vacuum of \(1 \cdot 10^{-6}\) mm Hg, and curve 4 is calculated. Analysis of the experimental data obtained showed that, when a vacuum of the order of \(1 \cdot 10^{-1}\) mm Hg is created, a sharp decrease in the dielectric strength of the medium is observed. Breakdown occurs even in those elements of the generator in which it was not observed during testing in air.
Further deepening of the vacuum showed that a vacuum of the order of \(1 \cdot 10^{-3}\) mm Hg is equivalent to operation of the generator in air, and only at a vacuum of the order of \(1 \cdot 10^{-4}\) mm Hg were electrical breakdowns between individual elements of the ESG partially eliminated.
It was possible to attain the calculated characteristic and almost complete elimination of breakdowns at a vacuum of the order of \(1 \cdot 10^{-6}\) mm Hg. In addition, it should be noted that the characteristics of breakdown voltages in vacuum are not stable. This was stated in [2] and was once again confirmed in the experimental investigation of the prototype generator.
Thus, preliminary tests of the experimental ESG model showed that such a design can operate quite satisfactorily in high vacuum.
REFERENCES
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A. P. Kononov et al. A small-size high-voltage source for operation in vacuum. Izv. TPI. Present collection.
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N. N. Slivkov, V. V. Mikhailov et al. Electrical Breakdown and Discharge in Vacuum. Atomizdat, 1966.