High Voltage

Difference between Internal and External Partial Discharge Sr. No. Internal Partial Discharge External Partial Discharge 1. This occurs mainly due to presence of voids or occlusions. This occurs mainly due to atmospheric conditions, the outer surrounding air gets ionized. 2. This is not visible to naked eye. This is easily visible in the form of … Read more

Partial Discharge in Solid Insulation The partial discharge (PD) is originated in voids/cavities, cracks or inclusions within a solid dielectric. Since the discharge is for only limited portion/area, it is known as partial discharge (PD). Causes of voids/cavities In case of epoxy material, gas-filles voids are caused due to air leaking into mould during curing … Read more

Breakdown Due to Treeing and Tracking Tracking is the formation of a permanent conducting path across the surface of an insulation. The spreading of spark channels during tracking in the form of the branches of tree is called treeing. The conducting film is usually moisture from the atmosphere absorbed by some form of contamination such … Read more

Discharge And Breakdown Due to Internal Discharge And Errosion Breakdown In practice it is difficult to produce a continuous homogeneous solid dielectric block. Usually voids or cavities are present in a solid dielectric or at the boundaries between dielectric and electrodes. They are of various shapes and sizes and volumes. These voide contain gas or … Read more

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