Electric Strength Of Vacuum Gap Research Articles

Method of Increasing the Electric Strength of Vacuum Insulation Using a High-Frequency Vacuum Arc

The effect of increasing the electric strength of vacuum insulation of gaps with electrodes from contact CuCr (≅30% Cr) material widely used in vacuum switches subject to conditioning with an AC vacuum arc modulated by high-frequency oscillations is considered. The modulating component stimulates periodic arc interruption and its ignition in new places thereby promoting effective treatment of the entire surface of the electrode pair. In addition, when the high-frequency arc is burning, the voltage drop across the electrodes significantly increases, thereby leading to alternating treatment of both electrode surfaces by intense high-energy flows of charged particles. For such treatment, the special regime of cleaning and local surface melting is used leading to the effective increase of the electric strength of vacuum gaps.

Pulsed Electric Strength of Vacuum Gaps

To plot unified dependences of breakdown voltage and electric strength on gap spacing, known experimental data for breakdown delay time in vacuum are analyzed and generalized. Analysis and generalization are realized from positions of the cathode- initiated breakdown. The data, which correspond to optimal modes of conditioning and are received at different experimental conditions for pulses of different shapes and durations in electric fields with a different degree of heterogeneity, are resulted in unified conditions for uniform field and rectangular pulse with given duration. Dependences of breakdown voltage U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> (d) and electric strength E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0br</sub> (d) on gap spacing d for copper electrodes in range 3times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> les d les 2times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> mm are plotted. At plotting curves U <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">br</sub> (d) and E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0br</sub> (d), the total voltage effect is considered. At pulses duration of t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> = 0.5 mus, the breakdown voltage makes up 2.5 kV for d = 3 mum and rises with interelectrode distance by three orders of magnitude up to 5 MV for d = 20 cm. The electric strength increases ~ 30 times from 2.5times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> V/m for d = 20 cm up to 7.5 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> V/m for d = 3 mum with decrease in gap spacing.

Electric strength of vacuum gap under various voltage conditions

Although the electric strength of vacuum gap under various voltage conditions has been discussed in many paper, research on this subject is still ongoing. The first page of our investigations was examining the prebreakdown state of vacuum gap under ac voltage excitation. Field electron emission in short vacuum gap (0–2 mm) and microdischarges in long vacuum gap (over 10mm) were analyzed. Field electron emission current was measured with an unbalanced hv bridge. Next, using voltage-current characteristics analysis, the parameters of field electron emission were obtained. The microdischarges phenomenon was monitored with a multichannel pulse-height analyzer. The relation between breakdown voltage and the parameters characterizing prebreakdown phenomena was then determined. Finally, the characteristics of electric strength under ac (50 Hz), switching impulse (250/2500 μs) and lighting impulse (1.2/50 μs) voltages were obtained. The investigations were carried out with CuCr contacts in a wide range of interelectrode distance (0.5–12 mm).

Pulse radiation effects in high temperature superconductors

Radiation effects in high temperature superconducting (HTSC) films, influenced by pulse electron and ion beams, are considered. The electron beams had kinetic energies E = 200–300 keV, current densities j = 10–2000 Acm2 and pulse duration tp = 0.3–1.2 μs; and ion beams of carbon, copper and silver with E = 200–350 keV, tp = 0.3 μs and j = 5–15 Acm2 were used in the experiments. The results of resistive threshold characteristics measurements by HTSC are described. Questions about the increase of critical current and electric strength of vacuum gaps with electrodes from HTSC are discussed.

Influence of electrode curvature of predischarge phenomena and electric strength at 50 Hz of a vacuum gap

The influence, in sphere-plane and ring-ring arrangements, of electrode curvature and microprofile on electron emission phenomena as well as on the electric strength of vacuum gaps is discussed. Improvement of the electrode microprofile was obtained by utilization of electropolishing technology. The nature of that technology is selective smoothing of the microneedles on the electrode surface. Optimum values of the electrode radius of curvature for various electrode distances have been determined. It was found that electropolished electrodes of various curvature resulted in increasing the electric strength of a vacuum gap by approximately 20-100%. >

Influence of electrode conditioning on the electrical strength of vacuum gap: A S Pokrovskaya-Soboleva et al, Zh Tekh Fiz, 41 (11), Nov 1971, 2363–2368 ( in Russian)

Influence of electrode conditioning on the electrical strength of vacuum gap: A S Pokrovskaya-Soboleva et al, Zh Tekh Fiz, 41 (11), Nov 1971, 2363–2368 ( in Russian)