Hi Chris:
Good question! My comment was an over-simplification. The following comments presume a constant clearance dimension between the electrodes. The variable is the air pressure. Another way to look at it: The more air you pack between the electrodes (the higher the air pressure), the greater the electric strength. Air breakdown starts with ionization of the air molecules. The EMF causes the ions to collide. The collisions then multiply exponentially and conduction occurs. The lower the air pressure, the easier it is to ionize the air molecules. However, there is a limit when the air molecules become scarce as the system approaches a vacuum. This limit is about 10**(-4) torr, about 138,000 feet altitude or 42,000 meters altitude. Vacuum breakdown is due to emissions from the electrode surfaces. The electric strength of a vacuum is in the order of 10**8 V/mm. Best regards, Rich On 2/28/2010 17:03, Carpentier Kristiaan wrote: > Hi Rich, > > Does this mean that higher up in space, where there is no air, there is > no insulation at all with a dielectric strenght breakdown value close to > 0V? > > Best regards, > > Kris Carpentier > > -----Original Message----- > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Richard > Nute > Sent: zaterdag 27 februari 2010 2:40 > To: Petrie, Craig D > Cc: emc-p...@ieee.org > Subject: Re: Creepage/Clearance and Altitude > > Hi Craig: > > > With regard to clearance, air is the insulator. > > As you go up in altitude, there is less air, > so there is less insulation. And lower > dielectric strength. > > So, to get the same amount of air (and the same > dielectric strength) between the two conductors, > you need more distance (clearance). > > Creepage is the interface between solid insulation > and air insulation. Physically, creepage cannot > be less than clearance. Degradation of the solid > insulation surface (creepage) is a long-term > effect largely due to deposition of foreign matter > on the insulation surface. > > > Best regards, > Rich > > > > > > > On 2/26/2010 04:12, Petrie, Craig D wrote: >> Hello, >> Can anyone tell me the link between creepage/clearance and altitude? > Why >> do these values need increased at greater altitudes? >> Regards >> Craig >> *Craig D. Petrie >> **Product Safety Engineer >> * >> - - 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <emcp...@socal.rr.com> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
