Hello Rich, I was not clear on the original post - there are two 'types' of transient immunity tests being referenced. The requirements for EMC standards, and the requirements for product safety standards. Some of the safety-specified transients are considered abnormal operations.
Study of the test parameters in IEC61051-2 has caused me to remove my regulatory hat and put on my reliability hat (similar to the Cat In The Hat headgear). I think that we have a potential life-time leakage problem for some VDRs. R/S, Brian > -----Original Message----- > From: Richard Nute [mailto:[email protected]] > Sent: Thursday, June 10, 2010 10:26 AM > To: Brian O'Connell > Cc: [email protected] > Subject: Re: VDR recommendations > > Hi Brian: > > > There are two parameters here - the max continuous rated > rms voltage > which is normal operations, and the 'clamping' voltage where the > component goes low impedance which is abnormal operations. We are > talking about the former; and the latter is not necessarily > part of any > safety requirement - other than the component shall not puke it guts > out during an abnormal operating condition. > > > > Just for clarification... a VDR has TWO "normal" operating > modes. At any voltage below the clamping voltage, the > resistance is high. At any voltage above the clamping > voltage, the resistance is low. > > Transient overvoltages are normal, not abnormal. This is > why we must address both operating and transient voltages > in product design. For example, electric strength is a > parameter that is based on the transient voltage. > > I believe thinking of a transient voltage as normal helps > in the design of equipment, and especially when a safety > engineer must interact with an equipment design engineer. > > 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: 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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
