Electrical breakdown strength

For powders, cp/pp is approximately one-half. If we further assume that the outer edge of the volume will go into corona when exceeds 3 V/micron, which is the normal electrical breakdown strength of a flat surface in air, Table II shows the maximum size containers that can be used for various net levels of particle charging without having the charge lost by corona. 

Some important dielectric behavior properties are dielectric loss, loss factor, dielectric constant, direct current (DC) conductivity, alternating current (AC) conductivity, and electric breakdown strength. The term dielectric behavior usually refers to the variation of these properties as a function of frequency, composition, voltage, pressure, and temperature. 

The physical properties of parylene films are remarkable Parylene is a very good insnlator with an electrical breakdown strength of up to 10 MV/cm, superior chemical stability, and high optical clarity. 

The electrical insulation properties of LCP are excellent, and because the LCP is homogeneous material, it is not prone to void formation as in fiberglass epoxy composite. The electrical breakdown strength of LCP is higher than polycarbonate—a plastic that is well-known for its good electrical properties. 

K.Y. Lau, A.S. Vaughan, G. Chen, I.L. Hosier, Polyethylene nanodielectrics the effect of nanosilica and its surface treahnent on electrical breakdown strength, in Annual Report -Conference on Electrical Insulation and Dielectric Phenomena, CEIDP, 6378712, 2012, pp. 21-24. 

Hosier IL, Vaughan AS, Swingler SG (1997) Structure-properly relationships in polyethylene blends the effect of morphology on electrical breakdown strength. J Matia Sci 32 (17) 4523 531... 

The dependence of the electrical breakdown strength on electrode separation has often been taken as an indication of the occurrence of an electronic avalanche. Careful measurements of the current through liquid n-hexane up to an applied electric field strength of 1.3 MV/cm at different electrode separations gave no evidence for collisional ionization in this molecular liquid (Sharbaugh et al, 1978). This is consistent with the tentative data on electron avalanches in liquid propane and cyclohexane which demonstrate that much higher field strengths are necessary. 

Humidity. The electric breakdown strength (and leakage) of dielectric elastomer transducers is often affected by humidity. Lower humidity can dramatically raise the breakdown strength of many dielectric elastomer materials. Humidity can be artificially lowered by using, for example, desiccants. Packaging is an issue for low-humidity operation however, most designs operate at atmospheric conditions. 

The addition of layered sihcates to epoxy resin improves the surface discharge endurance of the polymer, considerably increasing the time before electrical breakdown occurs (Montanari et al. 2005). The addition of nonconducting silica or alumina nanoparticles will reduce the conductivity of the polymer (Cao et al. 2004). Layered silicates have heen shown to increase the electrical breakdown strength and breakdown time (Imai et aL 2006), see O Fig. 55.6. This indicates that these materials may have potential applications for electrical insulation materials. 

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