I got Klaus Stimpers document referred to earlier in this thread: Thanks What I learned:
The theory assumes that most damage is done by small local discharges caused by a discontinuous conductive path (imagine condensation drops or small wet particles) called scintillations. These are micro sparks (visible with the right equipment) that create local temperatures well above 1000 degrees, and contribute to a local burning disintegration of the (carbon containing) base material in areas of about 0.2 mm. Once enough areas have been affected a full continuous (carbon) leakage path is created on the surface that may lead to further damage. This is a more or less statistical process. The size and frequency of these scintillations and affected areas seem dependent of the voltage and total damage is therefore a time integration of voltage over the creepage path. In my opinion this leads to the conclusion that an average voltage value should be choosen, Instead of rms, to determine creepage path, but I may overlook certain aspects. Correct me where I am wrong. Stimper states that leakage currents due to fully continuous conductive paths can be neglected, and only in the last phase of drying, sufficient discontinuities exist for scintillation. Alternating humidity conditions such as day/night rhythms, in relatively cold (need for condensation droplets) designs are most liable to creepage problems Gert -----Original Message----- From: John Woodgate [mailto:[email protected]] Sent: Tuesday, May 13, 2014 2:18 PM To: [email protected] Subject: Re: [PSES] Creepage and RMS In message <[email protected]>, dated Tue, 13 May 2014, "ce-test, qualified testing bv - Gert Gremmen" <[email protected]> writes: >The point is that creepage distances are determined such as that within >the limits of pollution degrees 1-3 , no substantial leakage >current(eventually leading to breakdown of the >insulation) develops. Yes the reaction starts immediately >(salt/electrodes) but the deterioration takes time. > >Testing with carbon would lead to infinite creepage distances. The document you cite admits the presence of conductive pollution Pollution degree 3 Conductive pollution occurs or dry non-conductive pollution occurs which becomes conductive due to condensation which is to be expected. – Pollution degree 4 Continuous conductivity occurs due to conductive dust, rain or other wet conditions. In the past, when commutator motors were widely used, carbon dust pollution was very common. Infinite creepage distances were not required. > >Apparently the relation between voltage and insulation deterioration >was derived very experimentally .... read here: In Table 2J, the transient voltages are specified as peak. In Table 1 (of a different standard), the 'rated' [sic] impulse voltages are not specified as peak so, under IEC rules, are to be taken as RMS. This is confusing. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Nondum ex silvis sumus John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK - ---------------------------------------------------------------- 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: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]> - ---------------------------------------------------------------- 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: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
