James D. Cobine

Analysis of Electrode Phenomena in the High‐Current Arc

An analysis is made of the phenomena at the electrodes of a high‐current short‐time arc. It is shown that the input power density to the anode spot is in the range 5×104 to 1×106 watts/cm2. To a first‐order approximation, all this power can be carried off by evaporation. Power conducted into the metal and lost by radiation is negligible in the probable operating range. For most materials, the anode spot is probably considerably above the boiling temperature. The process of evaporation holds the spot temperature constant at a value such that the input power and evaporation power are equal. Experimental data indicate that for any given metal the anode spot temperature is that for which the evaporation power density is at least 3×105 watts/cm2. As an example, for copper the theoretical limits of temperature are 2490 to 3040°K, while experimental data indicate a temperature of 2920°K. Other metals considered are: Ag, Al, C, Fe, Mo, Sn, Ti, W, Zn, Zr. It is also shown that for the maximum power input that can ...

Anode Phenomena in Metal‐Vapor Arcs at High Currents

The present investigation is concerned with the conditions associated with the development of an anode spot for metal‐vapor (vacuum) arcs. Chief among the aims of the investigation is the determination of the threshold current density for anode‐spot formation for a variety of electrode materials spanning a wide range of thermal and electrical properties. Electrodes of Sn, Al, Ag, Cu, Mo, and W were chosen for study in a plane‐parallel electrode geometry. Arcing was over one‐half cycle of a 60‐Hz current wave. The onset of anode‐spot formation was determined from high‐speed streak photographs of the discharge. An oscillographic record of the arc voltage was obtained simultaneously with the streak picture. From the data obtained particular interest attaches to the threshold current for anode‐spot formation, the threshold current density derived from it, and the arc voltage‐current characteristic. The threshold current densities (peak values) range from a low of 0.9×102 A/cm2 for tin to a high of 5.4×102 A/c...

Experimental Study of Arc Stability. I

The stability of short arcs in gases and in metal vapors is closely related to the phenomena associated with the cathode spot. Use is made of improved techniques to study this phenomenon for a considerable range of electrode materials. The distribution of arc life for a given average current is shown to follow the survival law. These data demonstrate that a small percentage of arcs of a given current on very clean metal surfaces may have lifetimes that are extremely short or very long compared with the average life. The relation between the average life of an arc and its average current is shown generally to consist of two sharply defined sections each of the form lnt=A lnI+B. The distribution of lifetimes and the relation between average life and average current are shown for Hg, Cd, Zn, Cu2Sb, Bi, Bi‐Cu, Cu‐In, Ag, Cu3Sn, Al, Be, Cu, Cu‐W‐Th, Cu‐MoC, Mo, and W. It is shown that high vapor pressure materials tend to produce more stable arcs than those having low vapor pressure.

The Electronic Torch and Related High Frequency Phenomena

This paper presents the design of a high frequency electronic torch operating at 1000 mc/sec, and some of the physical characteristics of the gaseous discharge produced. The flame produced by polyatomic gases is capable of melting many refractory materials due to the heat of association of the dissociated molecules. Monatomic gases produce little heat. Probe measurements indicate an electron temperature of the order of 105 deg K. The gas temperature near the outer edge of the flame appears to be of the order of 3000°K.

Research and Development Leading to the High-Power Vacuum Interrupter- A Historical Review

A history of the development of a successful, high-power vacuum interrupteris presented. This covers two principal phases: (1) early engineering effort in the late 1920s and early 1930s to produce a commercial interrupter, and (2) a review of the research and engineering at the General Electric Company covering new technologies necessary for the development of the high-power vacuum interrupter. A short review of the literature is included.

Research and development leading to high-power vacuum interrupters

Although the vacuum switch concept is more than 30 years old, reliable high-power vacuum interrupters did not become a reality until recently. In this article, the historical background of these vacuum interrupters is given

Recovery Strength Measurements in Arcs from Atmospheric Pressure to Vacuum

Measurements are reported for the recovery of electric strength following interruption of an arc drawn in nitrogen at pressures ranging from atmospheric to 0.02 torr. These data are compared with similar results obtained for vacuum arcs. Recovery strength measurements followed a single half-cycle of sinusoidal arc current with a peak of 400 amperes. For conditions of gap length and pressure described by the Paschen curve minimum, full recovery is reached in a time less than a few micro-seconds. The voltage corresponding to full recovery is essentially determined by contacts, their separation, and ambient gas pressure.

Stability of Arcs in Gases

A study has been made to determine the average duration of dc arcs in various gases at slightly higher than atmospheric pressure. These arcs were drawn between ¾‐in. copper contacts with power being supplied from a 125‐V dc generator. The experimental vessel, which contained about 1 liter volume, was provided with two liquid‐nitrogen traps through which gas was admitted and withdrawn. The gases studied were hydrogen, helium, argon, nitrogen, oxygen, and sulfur hexafluoride. It was found that in the current range studied (about 1 to 45 A) arc duration was always statistical and finite. This behavior is similar to that observed earlier for metal vapor (vacuum) arcs. For a given current, average arc duration increased for those gases in the order listed above. In the case of the latter two (O2, SF6), arc stability is believed to have been strongly affected by arc reaction products. It was concluded that for each of the gases studied, arc duration was greater than that found for a copper vapor arc at the same...

Electrode materials and their stability characteristics in the vacuum arc

The problem of current chopping in the vacuum interrupter is considered and various reasons for the occurrence of this phenomenon are explored. Metals with high vapor pressure were found to be most suitable for the maintenance of an arc at low currents in vacuum, and have been utilized for the solution of the current chopping problem in vacuum interrupters. There is some evidence that the presence of low work function materials also enhances arc stability.

Recovery Characteristics of a Triggered‐Vacuum Gap at High Currents

A system has been devised for use with a high‐current generator whereby the recovery‐strength characteristics of a triggered‐vacuum gap (TVG) may be determined. Data are presented for an experimental hydrogen‐triggered TVG for currents of 2000, 5000, and 10 000 A, the latter value being near the upper limit of the tube studied. The causes of data scattering are discussed.