High Voltage

Post Breakdown in Non-uniform Field and Applications (Electric Discharge) The passage of current through a gas is usually termed as electrical discharge in gases. This phenomenon is observed when a gas usually a non-conductor carries charge carrier in addition to the general gas atoms on molecules and becomes electrically conducting.  The electric discharge in a … Read more

Townsend’s  Current Growth Equation (Considering Primary and Secondary Ionization Both) I = I0 eαd [Considering only Primary ionization] I = I0 eαd / [1 – γ (eαd – 1)]  [Considering both Primary and secondary ionization] Let n0  be the number of electrons released from cathode due to UV radiations. n+ – be the number of electrons released from cathode due to the positive ion bombardment. nd  – … Read more

Time Lags for Breakdown of Electronegative Gases There is a time lag between the applications of a voltage sufficient to cause breakdown and the occurrence of breakdown itself. This laps time is known as statistical time lag (tS). The appearance of electrons is usually statistically distributed. After breakdown i.e. after the appearance of the electron, a … Read more

Paschens Law Q. State and explain Paschens Law ? It States that, ” Breakdown voltage of uniform field gap is unique function of product of p, i.e. electrode gap distance for a particular gas and for a given electrode material. Figure A According to Townsend’s breakdown Criteria y and α both are functions of E/P : … Read more

Townsend’s Criterion for Breakdown Equation I = I0 ead / I – γ (ead – 1) gives the total average current in a gap before the occurrence of breakdown. As distance between electrodes d is increased, the denominator of the equation tends to zero, and at some critical distance d = ds 1 – γ (exp (αd) – 1) = … Read more

Various Factors Influencing the Breakdown In Gases Q. Discuss the various factors which affects the breakdown of gases. Distance between electrode Shape of electrode Size of electrode Material of electrode Material in the gap  Temperature Pressure Applied voltage Polarity of the small electrode Humidity Dust Irradiation Nearby earthed objects Miscellaneous 1. Distance between Electrodes If … Read more

Townsend’s Current Growth Equation  At any distance x, let number of electrons be nx. Since current is the rate of flow of electrons, so we will start with the electron equation. dnx = nx.α. dx/ where, α = Townsends first ionization coefficient which represents the number of electrons liberated by a free electron due to its … Read more

Important Definitions about Ionization Q. Define Townsend’s first and second Ionization constant. How the condition for breakdown is obtained in a Townsend’s discharge ? Primary Ionization It is the process of liberation of free electrons from gas molecules with simultaneous production of positive ions due to collision with free electrons. Townsend’s Primary Ionization coefficient It … Read more

Types of Ionization Q. Explain the terms Ionization  and hence explain different ionization processes with reference to breakdown in gases ? Ionization by collision Photo ionization Secondary Ionization process Electron decay and attachment process 1. Ionization by Collision : The process of liberating an electron from a gas molecule with the simultaneous production of a … Read more