| Electric Strength of Dielectrics |
- The qualitative definition of 'electric strength' of a dielectric is 'the maximum electric stress a dielectric can withstand'.
- A large number of factors affect the electric breakdown of a dielectric, these include pressure, humidity, temperature, electric field configuration (electrode shape and size) electrode material, applied voltage waveform, its duration and magnitude, presence of impurities and imperfections in the dielectric, the composition of dielectric material. Hence a quantitative definition is complicated.
- In a time varying ac power frequency field (quasi stationary field), the maximum electric stress occur at the peak value of the applied voltage.
- Intrinsic strength of a dielectric: It is defined for gaseous and other than gaseous dielectric differently.
- Gaseous dielectric: It is the magnitude of breakdown voltage measured across a gap distance of one cm in uniform field (η = 1) at normal temperature and pressure.
- Liquid and Solid dielectrics: It is the highest value of breakdown strength obtained after eliminating all known secondary effects which may influence the breakdown adversely.
It is measured for the ideal conditions of the dielectric in uniform field. Since it is very very high for solid and liquid dielectrics compared to gaseous dielectrics, it is measured for mm and µm thin films of the liquid and solid dielectrics respectively instead of 1 cm gap distance in case of gaseous dielectrics.
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