Electronic – Delta-Star Combination Exercise

circuit analysisdeltaresistancestar

This post is regarding exersise 4-8 from the following book:
Hughes Electrical And Electronics Technology 10th Ed.

Here it is:

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Let's focus on what I tried for solving part (b) :

Since this is an exercise under the chapter for delta-star transformations my first thought was to try and perform some such transformation. However this was a combination of both star and delta connections so I didnt really know whether the resulting resistances would be in series / parallel or neither, with the already existing ones, so I tried both series and parallel:
enter image description here

However neither worked.

My next thought was that maybe I have understood something very badly about the resulting resistance of two points in a circuit. So after a little bit of digging I tried the following:
enter image description here

However I again got a wrong result in regards to the given answers at the end of the book.

Conclusion:

  • Which approach (if any) was correct?
  • If no approach was correct, which concept do I need to understand better?

Any help/hint is very much appreciated

Best Answer

To calculate equivalent resistance between A and N one approach would be -

1.look at NCB which is in Delta connected form

2.make NCB in star connection from delta by conversion formula

after that conversion you'll get a very simlified circuit which is very easy to solve

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