One of the most widespread 3 phase network topology transformation is now ready for use. Corresponding tutorial is:
http://www.cirvirlab.com/index.php/electric/108-delta-star-or-delta-y-transformation-simulation.html

as well as the calculator
http://www.cirvirlab.com/simulation/delta-star_transformation_calculator.php

I am curious about this post.
1. Was it a homework assignment?
2. Are there many people who would find it useful?
3. Is it not easier to derive the formula yourself than to remember
where it is in your files and how to use it?
4. Would a simple spreadsheet not do it?
5. Certainly Maple or Mathematica would find the comples
transformation a snap.

--

Sam

Conservatives are against Darwinism but for natural selection.

1)hopefully not for someone taking circuit theory where 3) is more useful
2)not really -it is one of the network theorems that is sometimes useful
3)absolutely true.
4)sure
5)yes- J or APL also work well
But- it is pretty!

However- how often have you needed such a calculator? Also, if so, how
often would you either look it up or work it out from scratch as I have
often done simply because I either forgot or was too lazy to look it up?
It is not a teaching tool.
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.

--

Sam

Conservatives are against Darwinism but for natural selection.

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).

I have seen transformations, in Wikipedia for example, where the
nomenclature is not symmetrical. That is why I would have used A=Z23.
B=Z31 and C=Z12. Because each resistor in the delta will have one and
only one resistor in the wye which is not touching it, the pairs of such
resistors are Aa, Bb, and Cc. If you know one of these products you know
them all. Knowing either the delta or the wye values give a nice
symmetrical equation for this product.
To my mind, the transformation was used to break a network down to
series and parallel connections that are easy to calculate. I almost
never did that. I used mesh currents to get a set of simultaneous
equations. Before that, the Kirchhoff laws were the way to go. With
modern computers, there is hardly any reason to use the transformation.
The only benefit I can think of is that comparison of the delta and wye
equivalents gives some insight into a particular combination.
It could be that I am missing the entire point.

--

Sam

Conservatives are against Darwinism but for natural selection.

You are right- One does need double subscripts to deal with this
properly. You know what is going on and the format and have put the clue
in considering the "one and only resistor in the wye that is not
touching" You use, properly a double subscript notation. Dealing with an
idiot box, inputis of the form a b c where awhat is referred to may be
Zab,Zbc, Zca or in the reverse case Zan,Zbn, Zcn. Check it out regarding
the preservation of the terminals A B C.
As to the need for the transformation- I agree- use Kirchoff.
From my viewpoint as it appears is yours, use of I =YV (mesh) is
better than V-ZI (loop) simply because in most cases it results in
fewer simultaneous equations and is generally better for computer
modelling because once a choice of reference bus is made (in power
systems it is easy), the rest can be automated. It is messier with loop
methods as there are so many choices.

What I see too often on posts here is that they are from people who can
do what they were taught but unable to adapt to slightly different
situations. They work by handbook standards but without true
understanding. They are the ones who complained about trick problems in
class.
Much of life IS a sequence of TRICK PROBLEMS.

--

Sam

Conservatives are against Darwinism but for natural selection.

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