High voltage insulation

Lasdy, the importance of electroceramic substrates and insulators should not be overlooked. Here one strives to raise the breakdown strength by eliminating the interesting conduction mechanisms just described. Spark plugs, high voltage insulators, and electronic substrates and packages are made from ceramics like alumina, mullite [55964-99-3] and porcelain [1332-58-7]. 

R. V. Latham, High Voltage Insulation, Academic Press, Inc., New York, 1981. 

Alumina produced by the Bayer process is precipitated and then calcined [Krawczyk, Ceramic Forum International, 67(7-8), 342-8 (1990)]. Aggregates are typically 20 to 70 [Lm, and have to be reduced. The standard product is typically made in continuous dry ball or vibra-toiy mills to give a product d o size of 3-7 [Lm, 98 percent finer than 45 [Lm. The mills are lined with wear-resistant alumina blocks, and balls or cylinders are used with an alumina content of 80-92 percent. The products containing up to 96 percent AI9O3 are used for bricks, kiln furniture, grinding balls and liners, high voltage insulators, catalyst carriers, etc. 

High voltage insulation materials, self-cleaning coatings for, 22 123 High Volume Instrument (HVI) systems, for classifying cotton, 8 13-14 High water velocities, in industrial water treatment, 26 141... 

Coaxial cable connectors, terminal and high voltage insulators transformers, relays, antennae, power amplifier components. .. 

Polyurethanes can be used in applications where electrical properties are important. They are not normally used for high-voltage insulation. Polyurethanes are often used directly or in combination with epoxies for encapsulation. The addition of antistatic agents to polyurethane gives a product with the correct electrical properties while retaining the excellent wear needed for a number of roller-type applications. 

Fluorine is also used for the manufacture of sulfur hexafluoride (SF6) for high-voltage insulation and for uranium hexafluoride. Fluorine is used directly or combined with higher metals (cobalt, silver, cerium, etc.) and halogens (chlorine and bromine) for organic fluorinations and the growing production of fluorocarbons. 

For high-voltage insulators in service the contact angle is an abstract property that is not easy to measure and has to be interpreted. To con jare the influence of transfer of LMW into an artificial pollution layer on the leakage current, a high-voltage electrode arrangement as shown in Fig. 6 was used. 

Cycles of pollution and cleaning of silicone rubber samples show that hydrophobicity transfer is a dynamic process that depends on the amount of freely diffusible fluid components. It seems probable that the transfer effect is present during the whole lifetime of a silicone rubber for high-voltage insulators. 

Figure 10-12 Comparison of Outdoor High Voltage Insulators...

Insulating Oils high voltage insulaling oil 70 90 -0.9 0.7 100.2 Mitsubish iupital F20-02... 

Though polymers made specifically for high voltage insulation are remarkably clean, occasional contaminants occur and contribute to the deterioration of dielectric properties. Some of these are polymeric in nature such as gels or prematurely corsslinked polyethylene particles which may appear amber to dark brown in color depending on heat history. Figure 5 shows one... 

The internal stress whether initially present in the freshly made cable or developed during service life could have deleterious effects. Patsch (20) shows no effect of either the cusp or of areas with distinct flow pattern on the dielectric strength in high voltage insulation beyond the 95% confidence limit. 

---