Why do we need this?
How do we use this information to help with our design?
The reason for this was quite simple - to calculate snubber resistors
for the rectifying diodes.
Now after I ran few simulations it appears that it really doesn't matter
that much if the stray inductance is 15nH or 5nH, with the inter-winding
capacitance of ca 65pF the ringing is damped in 2-3 periods in both of
these situations using the same (510ohm) resistor value...
Personally I have found Jim Hagerman's article on snubbers completely useless. You have a bunch of DIY'ers running around mad trying to measure or calculate transformer parameters to determine what value R and C are appropriate. Just throw a scope on it and determine optimal values by experiment. You can get amazing results with a very simple process. No math needed.