Principle of Streamers Theory With positive polarity of the point Figure A (a) an electron formed in the gap, while moving towards the point, falls in the region of strong field, starts ionizing and forms an electron avalanche. If voltage between the electrodes increases slowly upto the time of formation of the corona (i.e. fulfilment … Read more

Streamer Theory or Kanal Theory Q. Explain the streamer theory of breakdown in air at atmospheric pressure. A narrow river of conducting particles. Stage when secondary avalanche (due to positive ions) has crossed. Streamer has crossed 1/2 the gap length. Gap has been bridged by a conducting channel i.e. Streamer. Figure A Figure B The … Read more

Comparison between Positive Corona and Negative Corona Sr. No. Positive Corona Negative Corona 1. Nature of discharge : With positive electrode corona discharge is in the form of uniform sheath all over the conductor surface. With negative electrode, corona discharge is spotty or filamentary all over the conductor surface. 2. It appears smaller than negative corona. It … Read more

Comparison Between Uniform Field and Non-uniform Field Sr. No. Point of comparison Uniform Field Non-uniform Field 1. Definition When electric field intensity is same everywhere in a gap and both electrode surfaces then it is known as uniform field. When electric field intensity is different everywhere in the gap and also on electrode surfaces it is known … Read more

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