I've also seen this effect when testing component power supplies (off-line switch-mode converters, 50-500W).
The problem became apparent when a customer added another EMI filter ahead of our power supply, creating a system we didn't anticipate. The power supply alone passed the test, but the additional EMI filter and power supply would not pass the common-mode surge test. When I sketched the AC input circuit of the composite system, I realized the surge generator was simply pulsing into several common-mode inductors and primary-ground capacitors - the circuit had no load! I set the surge generator to a relatively low voltage (200V), and connected an oscilloscope probe from the power supply AC input terminal to chassis. I saw the 200V surge ring to almost 400V! If this had been a 2kV common-mode surge, I expect that the power supply would see about 4kV primary-ground, which it was clearly not designed for. I think performing this simple test would be your best indication of surge voltages seen in your system. Since it involves primary-connected components, be sure to observe proper safety precautions. [email protected] wrote: >When troubleshooting surge problems on products we often see the surge pulse >to >be much higher after the line filter (testing the AC Mains with Line-Earth >surge >pulses according to EN61000-4-5). > >Can someone explain the science behind this and what effect the load might >have? >Can this increase in the surge potential be anticipated ahead of time so proper >clearances can be designed in? ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [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.rcic.com/ click on "Virtual Conference Hall,"
