I have some questions that are probably old hat to some of you but have me running in circles! I would take these to my TUV contact, but its a holiday south of the 49th! Any help would be appreciated.
The discussion relates to a high-frequency switching transformer with a primary (mains) winding and an SELV winding. The core is ferrite and is floating (ie not conductively connected to anything). While ferrite is only electrically conductive to the level of a few thousand ohms (according to my DMM), I have treated it as a conductive part. The core is not accessible. 1. We need to meet Reinforced insulation requirements from primary to SELV. Does it matter what insulation level we have from primary to the core and from secondary to the core? In other words can the core be simply treated as an interspersed conductive part which counts for zero in creepage and clearance measurements from primary to secondary? If so, does it matter how the total is divided - can most of it be on one side or the other, or do you have to meet at least Basic from each winding to the core? 2. Does our varnish impregnation help us in any way? It covers the complete core and windings, but obviously not the coil terminations. 3. Is hipot testing required from either winding to the core or just between the windings? Table C.2 only gives hipot requirements to the core if you are trying to achieve Basic or Reinforced insulation from a winding to the core. Thanks in advance for your help, Jim Eichner Statpower Technologies Corporation [email protected]
