Brain, Just going through that problem here too. Three variations of a product, two pass hi-pot and one fails. Tracked problem to hi-pot tester itself. Seems that it trips at 40 mA at 1,500 VAC. This turns out to be a limitation of the hi-pot tester. Further testing shows the system passes hi-pot at 1,500 VAC, but the current is 48 mA. So I am sending my testers back to the factory to have them upgraded to allow higher current before tripping during hi-pot.
In the process, research shows that trip current for failing hi-pot is manufacturer's choice. There is no current limit specified in either EN 50116 or EN 60950. My TUV engineer tells me a reasonable rule of thumb is that current during hi-pot can be up to 10 times the measured leakage current of the system. Seems to fit in with my experience here. Also had another failure problem. This time, one system and three testers. Two testers failed the system while one passed it. This problem was with ramp rate. That is, how long it takes to go from zero volts to 1,500 VAC. Again, there is no specified ramp rate in the standards and is set at manufacturer's choice. All three testers had different ramp rates (375 V/sec to 200 V/sec). Slower rate passes while faster rates failed. Finally set all three to 100 V/sec and problem solved. Lastly, that little buzzing sound heard during hi-pot test is probably corona discharge. Not harmful, usually, and not a failure. I think arcing is that little blue spark that has a fairly long lifetime, say seconds or so and I think flash-over is akin to a flashbulb going off. Both of these would be a failure in my book. To me, breakdown is like a short circuit. It may take several hundred volts to achieve, but once the hole is opened, it stays that way. This is just a layman's point of view. I would appreciate any expert corrections provided. Regards, Scott [email protected]
