Hi Bob:
If there is no insulation failure, the current increases linearly proportional to the increase in the test voltage. If there is an insulation failure, "...the current... rapidly increases in an uncontrolled manner." In other words, if there is an insulation failure, the increase in current is not linearly proportionally to the increase in applied voltage. This means that the resistance of the insulation is decreasing non-linearly with applied voltage. Failure of solid insulation usually results in a carbon path through the insulation -- a resistor that increases or decreases in value as a function of the duration of applied voltage and as a function of the value of the applied voltage. Failure of solid insulation rarely results in a short circuit, i.e., 0 ohms. In some cases, if the test is sustained, the power dissipated in the carbon path can cause it to open, and the test may appear to be passed. Consequently, there is no specific current that indicates an insulation failure. Another possible insulation failure is that of an insufficient clearance. In this case, the air breaks down and an arc occurs. In most cases, the tester will detect the arc current and terminate the test. Depending on the construction, the arc can have various currents, from low to high. A low-current arc can be of a sufficiently low current that the tester will not trip. The only way to detect a low-current arc is to look and listen. Some testers are specifically designed to detect arcs for any value of test current. Best regards, Rich From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Robert F. Keller Sent: Thursday, November 13, 2008 8:36 AM To: emc-p...@ieee.org Cc: Robert Keller Subject: Current limit for Dielectric Test Hello Group, I have a question regarding the Electric Strength test in 60950-1 section 5.2. It says in that section that you have a failure or the insulation broke down when the current which flows as a result of the application of the test voltage rapidly increases in an uncontrolled manner. So, is there an exact current limit at which it is considered to have "shorted"? And if so, is this printed in any standard? Any insight in this would be greatly appreciated. Best Regards, Rob Keller Senior Engineer Communication Certification Laboratory Ph.: 801.972.6146 Ext.237 Fax: 801-972-8432 r...@cclab.com - 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...@ptcnh.net> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
