Vacuum Breakdown: In the Townsend type of discharge in a gas described earlier, electrons get multiplied due to various ionization processes and an electron avalanche is formed. In a high Vacuum Breakdown, even if the electrodes are separated by, say, a few centimetres, an electron crosses the gap without encountering any collisions. Therefore, the current …
Vacuum Insulation: The idea of using Vacuum Insulation purposes is very old. According to the Townsend theory, the growth of current in a gap depends on the drift of the charged particles. In the absence of any such particles, as in the case of perfect vacuum, there should be no conduction and the vacuum should …
Gases and Gas Mixtures for Insulation Purposes: Over the years, considerable amount of work has been done to adopt a specific gas for practical use. Before adopting a particular gas or gas mixtures for a practical purpose, it is useful to gain a knowledge of what the gas does, what its composition is, and what …
Post Breakdown Phenomena in Gases: This is the Post Breakdown Phenomena in Gases which occurs after the actual breakdown has taken place and is of technical importance. Glow and arc discharges are the Post Breakdown Phenomena in Gases, and there are many devices that operate over these regions. In a Townsend discharge (see Fig. 2.20) …
Breakdown in Non Uniform Fields: In Breakdown in Non Uniform Fields, such as coaxial cylinders, point-plane and sphere-plane gaps, the applied field varies across the gap. Similarly, Townsend’s first ionization coefficient (α) also varies with the gap. Hence αd in Townsend’s criterion [refer to Eq. (2.22)] is rewritten by replacing αd by Townsend’s criterion for breakdown …
Corona Discharges: If the electric field is uniform, a gradual increase in voltage across a gap produces a breakdown of the gap in the form of a spark without any preliminary discharges. On the other hand, if the field is non-uniform, an increase in voltage will first cause a discharge in the gas to appear …
Paschen Breakdown | Paschen’s Law | Paschen curve It has been shown earlier (refer Sec. 2.6) that the Paschen Breakdown criterion in gases is given as where the coefficients α and γ are functions of E/p, i.e Substituting for E have in the expressions for α and γ and rewriting Eq. (2.26) we have This equation shows a …
Streamer Theory of Breakdown in Gases: Townsend mechanism when applied to breakdown at atmospheric pressure was found to have certain drawbacks. Firstly, according to the Townsend theory, current growth occurs as a result of ionization processes only. But in practice, breakdown voltages were found to depend on the gas pressure and the geometry of the …
Formative Time Lag: Formative Time Lag – In the previous section, the mechanism of spark breakdown is considered as a function of ionization processes under uniform field conditions. But in practical engineering designs, the breakdown due to rapidly changing voltages or impulse voltages is of great importance. Actually, there is a time difference between the …
Experimental Arrangement to Measure Ionization Coefficients α and γ: The Experimental Arrangement to Measure Ionization Coefficients is shown in Fig. 2.2. The electrode system consists of two uniform field electrodes. The high voltage electrode is connected to a variable high voltage d.c. source (of 2 to 10 kV rating). The low voltage electrode consists of a …
Experimental Arrangement to Measure Ionization Coefficients Read More »
