Rich, I agree that manufacturers of some dielectric testers add lots of extra features that are not required for performing type-tests. Perhaps this reflects the fact that more testers are sold into a production environment where the requirements are different. For performing type-tests I like a tester where I can ramp up the voltage manually and turn off the overcurrent trip: this enables me to hold the insulation that is breaking down at a point where I can maintain the fault and thereby see where the problem is. Such features are completely useless in a production environment where the object is to automate the test so that they can be performed by people who know nothing about creepages and clearance distances and have no need to perform failure analysis. The advantage of relatively complex hipot testers is that they can be set up to ramp the voltage a predetermined rate, maintain the voltage for a given time, and detect different aspects of current flowing and trip accordingly - thus complexity in the equipment can result in simplicity of use IF THE PERSON DEFINING THE SETUP UNDERSTANDS THE VARIOUS PARAMETERS. However, in the many years I've been involved in product safety I have seen many FALSE failures caused by incorrect settings. Some examples include: - not taking account of the expected leakage current of RFI filters when using an ac test voltage - not taking into account the di/dt that you should expect when charging Y-capacitors from a dc source when setting the ramp time - thereby making the overcurrent device 'think' that a fault has occurred - not taking into account the tolerance of RFI suppression components, or use of alternate components with different capacitance values, when setting the trip point - not taking trouble to understand the more esoteric trip techniques and proving them in the lab before rolling them out into a mass-production environment - not taking into account that the parameters may need to change between different models of equipment. So, before looking for a CAUSE of a breakdown, my suggestion is to VERIFY if the breakdown is real, or just a MEASUREMENT ERROR. If the problem is caused by a measurement error, then agreeing the hipot settings with your NRTL are most definitely of consequence. Regards, Richard Hughes In a message dated 08/19/2004 17:51:11 GMT Standard Time, [email protected] writes:
Today's hi-pot testers are just too sophisticated. They tend to give indications of performance of the various dielectrics and not necessarily indication of the true electric strength of a safety-required insulation. The hi-pot settings are of no consequence whatsover in your dealings with the NRTL. The only thing that counts is the *CAUSE* of the alleged breakdown. ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
