All transformers are phase inverting. The lowest leakage point of primary and secondary windings relationship to conventional E/I and C core is the physical start of the helical spiral winding. This is assuming more than one layer of wire. In toroid's the spiral wraps around the core and there is no lowest leakage point, except for the one developed capacitively between primary and secondary, unless there is a second or more traverse. Because the windings couple both inductvely and capacitvly to the core and each other, you develop ringing that generates eddy currents on all adjacent ferrous and non ferrous metallic surfaces. These couplings are what drive circulating currents in chassis and provide antenna emitters for circuits. Any winding with AC voltage above safety low voltage potential (33 vac RMS) should be suspect. Most of them will be inert with respect to the chassis, but if you have more than one transformer involved, they can cross couple.
There are no mathematical solutions for these events. Ralph Morrison published a book, "Grounding and Shielding Techniques" that is the only useful book I know of. Not a lick of math to be found. The RDH 4 does have the usual delicious hints, but no practical solutions. There is other good work out there, but it is not readily available, being under the seal of the AES, with not enough of an abstract to know if you can extract useful information for your money. Plenty of room here for misunderstandings and "entrepreneurs". |
|