The Physics Factbook™
Edited by Glenn Elert -- Written by his students
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|Pillai, S.O. Solid State Physics. New Age International, 2005.||
|"Dielectric Materials." McGraw-Hill Encyclopedia of Science and Technology, 10th Edition, 2007.||"At room temperature, E* is 500-700 MV/m; and over a wide frequency range, for commercial polyethylene...."||500-700 MV/m|
|Vaughan A.S., Zhao Y., Barré L.L., Sulton S.J., and Swingler S.G. European Polymer Journal 39. Elsevier B.V., 2003: 355-365.||"Alternatively, restricting discussion, initially, to just Materials A and B, examination of Fig. 8 indicates that, for both systems, all the quenched materials have measured breakdown strengths that fall below the global mean of 162.7 kV/mm.... Materials A and B, quenching directly from the melt leads to mean breakdown strength values in the range 154-160 kV/mm."||154-160 MV/m
162.7 MV/m (Mean)
|Halliday, David and Robert Resnick. Physics Parts I & II. John Wiley & Sons, Inc., NY, 1966.||
|Lide, David R. Handbook of Chemistry and Physics, 88th Edition. CRC Press, Taylor & Francis Group, New York, 2007-2008.||
In a dielectric, or an electric insulating material, electrons are bound to atoms and molecules and there is a high resistance to electric current, which means that the material has a zero or near zero electrical conductivity. When breakdown occurs, the present electric field frees the electrons. If the electric field is strong enough, the freed electrons may accelerate and liberate other electrons when they collide with neutral atoms or molecules. The liberation of electrons may turn the material into a conductor with its positive charge. In order to calculate how much the voltage an insulating material can hold before breaking down, the dielectric strength of the material must be found, which is measured in volts per unit length. The higher the electric strength, the more useful is the material as an insulator.
Dielectric strength is a property of an insulating material and it is defined as the ratio of the breakdown voltage to the material's thickness. Breakdown voltage is the maximum voltage a material can withstand before a conducting path forms through it.
Polyethylene (plastic) is a tough inexpensive polymer made of long chains of carbons attached with hydrogens. It has fine electrical properties with its low moisture absorption, however, as the temperature increases, it tends to soften as its crystallites melt and its dielectric strength will decrease. The dielectric strength of polyethylene varies based on many factors, so they range from 18.9 MV/m to 160 MV/m.
Cherry Xu -- 2009
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