Thermal Breakdown No solid is perfect electrical insulator, hence under an electric field small conduction currents always flow in a solid. This flow of current causes local area’s and heating created by the collision of electrons with the lattice by I2R losses. Under A. C. voltage by the energy absorbed by the solid in an … Read more

Electrochemical Chemical Breakdown These are much related to ‘thermal’ breakdown. Temperature rise in an insulating material (due to losses etc.) accelerates the chemical deterioration. Electrochemical deterioration is due to the presence and mobility of ions is the insulation which are responsible for leakage current and energy loss in the material. In the presence of air … Read more

Electromechanical Breakdown When a dielectric material is subjected to an electric field electrostatic compressive stresses are developed, charges of opposite nature are induced on the two opposite surfaces of the material and hence a force of attraction is developed and the specimen is subjected to electrostatic compressive forces and when forces exceed the mechanical withstand … Read more

Avalanche Breakdown An electron entering the conduction level of the dielectric at the cathode will move towards the anode under the effect of electric field. During the movement it gains energy and on collision it loses a part of energy. If mean free path is long energy gained due to motion is more than lost … Read more

Frochlich’s Theory Electronic Breakdown/ High Temperature Breakdown On a pure dielectric the valance band is separated from conduction band by a very large energy gap. Electron’s can’t acquire enough energy to jump to the conduction band. (to remove an electrons from the atomic structure a field of the order of 10’v/cm is required. But normally … Read more

Breakdown in Solids The mechanism of breakdown in solids is less understood because of it complexity. When breakdown occurs gases regain their dielectric strength fully, liquid partially and solid lose their dielectric strength completely. It is permanent breakdown. Breakdown depends upon : Magnitude, time of voltage applied, A.C, D.C, or impulse voltage applied. Ambient temperature, … Read more

Breakdown Mechanisms Short term breakdown Long term breakdown Short-Term Breakdown If electric field stresses are very high, failure occur in seconds or even faster without any damage to the insulating surface prior to breakdown. When applied voltage close to breakdown value, breakdown occurs in one or more discharges. When stress exceeds the critical stress at … Read more

Breakdown and Conduction in Solids Composite Dielectrics It is difficult to imagine complete (perfect) insulation system, in an electric equipment. We have combination of dielectric materials. The solids may have voilds, having filled with gases; liquids may have suspected solid impurities, dirt, dust etc. Insulation system having combination of more than dielectrics in series and … Read more

Alternative Liquid Insulators The use of mineral oil in conjuction with solid insulation is followed for many years. Esters Ester based fluids have good biodegradability and these have high flash point. The modern complex electrical supply system demands high degree of safety. Due to high flash point property esters are more safe. These are particularly … Read more

Transformer oil Filtration The transformer oil due to its repeated use comes in contact with moisture, dust, dirt, temperature, sludge formation and becomes impure and it is to be reconditioned so that it can be used again and again. For this purpose the oil is to be filtered in a filter plant. Due to filtration; … Read more