Why does air (or any insulating material) have decreasing dielectric strength, kV/mm, with increasing distance through the dielectric substance? Assume homogenous field. (I have assumed the dielectric strength was constant for the material.) In other words, what is the physical basis for the non-constant dielectric strength clearance tables in various safety standards? (I have yet to find the answer from the web.) How can I predict the dielectric constant for a given distance through air (or any insulation)?
Charles J. Fraser, in Mechanical Engineer's Reference Book (Twelfth Edition) <https://www.sciencedirect.com/book/9780750611954/mechanical-engineers-refer ence-book> , 1994: If the potential difference across opposite faces of a dielectric material is increased above a particular value, the material breaks down. The failure of the material takes the form of a small puncture, which renders the material useless as an insulator. The potential gradient <https://www.sciencedirect.com/topics/engineering/potential-gradient> necessary to cause break down is normally expressed in kilovolts/millimetre and is termed the 'dielectric strength'. The dielectric strength of a given material decreases with increases in the thickness. Table 2.2 gives approximate values for some of the more common dielectric materials. Table 2.2. Dielectric strength of some common insulators Material Thickness (mm) Dielectric strength (kV/mm) Air 0.2 5.75 0.6 4.92 1.0 4.36 10.0 2.98 Mica 0.01 200 0.10 115 1.00 61 Thanks, and best regards, Rich - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to [email protected] All emc-pstc postings are archived and searchable on the web at: https://www.mail-archive.com/[email protected]/ Website: https://ewh.ieee.org/soc/pses/ Instructions: https://ewh.ieee.org/soc/pses/list.html (including how to unsubscribe) List rules: https://ewh.ieee.org/soc/pses/listrules.html For help, send mail to the list administrators: Mike Sherman at: [email protected] Rick Linford at: [email protected] For policy questions, send mail to: Jim Bacher: <[email protected]> _________________________________________________ To unsubscribe from the EMC-PSTC list, click the following link: https://listserv.ieee.org/cgi-bin/wa?SUBED1=EMC-PSTC&A=1
