From: dhky@shaw.ca   
      
   On 24/10/2013 8:47 PM, Salmon Egg wrote:   
   > In article , Don Kelly    
   > wrote:   
   >   
   >> I have dealt with a lot of circuit analysis over the last  60 years but   
   >> over this time, my use of star delta transformations has declined   
   >> considerably as   
   >>    (a)I am looking for complete circuit solutions   
   >>    (b)If I am trying to reduce a circuit to a thevenin model--why bother   
   >> when there are more powerful methods such as Z-bus which take advantage   
   >> of the computer.   
   >> (c) In relatively few cases I want to use this for its own sake.   
   >>   
   >> Admittedly this calculator may be  useful as part of a set of tools   
   >> -provided that set was all in one place and results could be saved and   
   >> applied elsewhere. To some extent a language such as APL or J then   
   >> allows considerable freedom along with the use of pre-defined   
   >> transformations such as the delta-wye. As an aside, in J, the delta-wye   
   >> transform and the y-delta transform each take one short relatively   
   >> readable line. As with Patrick, I am sure that I learned more about   
   >> programming than  about the theory.   
   >   
   > I agree fully with Don. It is more trouble to keep track of such a tool   
   > than it is to look it up or derive. When you do get to the tool, you   
   > also have to figure out how to use it. In my case, my reason for using   
   > the transformation was mostly to study the transformation's properties   
   > than a need for the transformation itself. It has some interesting   
   > attributes.   
   >   
   > For example, use upper case letters to label the delta resistors (or   
   > impedances). Use lower case letters for the Y such that A and a do not   
   > touch, etc. Then A, B, C, a, b, c form three balanced bridges.   
   >   
   > A*a = B*b = C*c = A*B*C/(A+B+C) = a*b + b*c + c*a.   
   >   
   > Thus, once you do one of the two calculations on the right, you have the   
   > cross multiplication product that balances the bridges.   
   >   
   This is interesting -you have hit a core of the problem. Going from A   
   (Z12) B (Z23c) C (Z31) to a b c or z1n z2bn z3n works nicely -i.e going   
   delta to wye. However there may be a problem going the other way- to   
   deal with this one must say Z12 =A =(z1n*z2n +z1n*z3n+z2n*z3n)/ z3n or   
   (ab+ac+bc)/c   
   The problem is that the numbers are right but as you have indicated A   
   and a do not touch. There is a rotation which is a problem of   
   nomenclature - what is fixed is the terminals 1, 2,3  and we are dealing   
   with Z12 etc or z1n etc (n being a 4th or neutral terminal not present   
   in the delta).   
   --   
   Don Kelly   
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