High Voltage Vacuum Insulation Research Articles

High-voltage vacuum insulation with epoxy-coated cathodes

High-voltage vacuum insulation with epoxy-coated cathodes

Lichtenberg Figures Produced by High-Voltage Discharges in Vacuum

The formation of Lichtenberg figures on aluminum and titanium electrodes covered by oxide and nitride layers while being exposed to high vacuum and 100-kV (rms) 60-Hz voltage is recorded. The observations were made in the course of research on high-voltage vacuum insulation for cryocables. The Lichtenberg figures have several technological implications. They provide evidence for the occurrence of 1) focused ion beams, and 2) tangential discharges in the adsorbed layer of gas on the vacuum side of dielectric coverings on metal conductors. As Lichtenberg figures can only be produced by fast high-voltage pulses, they prove that the discharge duration was short compared with the period of the 60-Hz voltage wave.

Mechanism of Surface Charging of High-Voltage Insulators in Vacuum

In vacuum, the surface of insulators becomes electrically charged when subjected to high-voltage stresses. The charging mechanism is described. A model simulating the charging shows that the surface charge densities are proportional to the applied voltage and depend on the secondary electron emission of the dielectric surface. It is also time dependent. Surface charges are shown to explain many results obtained in studies of insulator surface breakdown.

High-voltage conditioning at large gaps in industrial vacuum

The improvement of high-voltage insulation in vacuum by ageing the electrodes is well known. This so-called conditioning effect becomes very important if ultra-high-vacuum techniques cannot be employed in systems with large dimensions. For unbaked surfaces this effect allows one to increase the initial field strength by a factor of about 10. In the present paper, the electrode gaps were variable between 15 and 30 cm. For such gaps, the conditioning and also the deconditioning process which occurs when the high voltage is removed have been studied. An attempt has been made to describe these processes mathematically, and to understand the mechanism involved. The results are compatible with the hypothesis that these effects are due to a change in the adsorbed gas layer; that is, a change in the workfunction of the electrode material.

High-voltage multi-section vacuum insulator of semiconducting glass ceramics: V A Rgakov et al, Prib Tekh Eksper, No 5, 1971, 226–228 ( in Russian)

High-voltage multi-section vacuum insulator of semiconducting glass ceramics: V A Rgakov et al, Prib Tekh Eksper, No 5, 1971, 226–228 ( in Russian)

Electrical differentiation for energy-loss analysis

An experimental arrangement is described which was set up to measure the energy loss spectra of electrons which have passed through thin specimens in the electron microscope. It consists of a nondispersive filter lens which rejects electrons of less than a certain energy, determined by the voltage of the central electrode. By modulating this voltage with a small ac component and measuring the resulting modulation of the transmitted beam, the apparatus can be used as an energy analyser. In this paper, the process of `differentiation by modulation' is reviewed and the effects of using different waveforms and frequencies examined. Also discussed are high-voltage insulation and breakdown in vacuum, the effect of focusing the beam on the phosphor (which was used as the electron detector), and limitations upon possible sweep speeds. A novel feature of the system is a 2 kHz optical link used to supply a synchronizing signal to the high-voltage line. The energy resolution of the system comes close to the theoretical minimum of about 1?5 eV. At low accelerating voltages output noise is almost entirely shot noise, but above 60 kV microdischarges increase the noise level substantially. Noise from these two sources limits the usefulness of the system for measuring low currents.

Economic Assessment of a Liquid-Nitrogen- Cooled Cable

This paper outlines the design of a rigid underground line for transmitting electrical energy with tubular aluminum conductors cooled internally by liquid nitrogen and supported on suitable dielectric spacers in high-voltage vacuum insulation. The installed cost of a specific line with terminations and refrigerators has been estimated and found to be easily competitive with oil- paper insulated pipe-type cables of ratings in excess of 1000 MVA and in the voltage classes 138, 230, and 345 kV. It is shown that the nitrogen-cooled cable has great operating flexibility in so far that it may be adapted to long-term load growth, emergency over- loads, and repetitive load fluctuations of daily, weekly, and seasonal cycles. The first commercial installation, it is argued, may come into service before 1975.

Phenomena at the metal-dielectric junctions of high-voltage insulators in vacuum and magnetic field

Phenomena at the metal-dielectric junctions of high-voltage insulators in vacuum and magnetic field