 Hello everyone. Myself, Sanjay Uttgay, assistant professor, department of electronics engineering, Valchan Institute of Technology, Solapur. Today, we are going to discuss TC Circuits Part 1, Conversion from Star to Delta Network. At the end of this session, students will be able to analyze complicated electrical circuits. Guidelines, Introduction, Star Network, Star to Delta Conversion and Delta to Star Conversion are references. Introduction. In the earlier session, we discussed Delta to Star Conversion. Now, the question is why Star to Delta and Delta to Star Conversion is necessary? In some complicated circuits, we are having a series and parallel networks. To simplify such networks, we took help of Ohm's law, KCL, Kirchhoff's voltage law and so many. But there are some complicated networks in which we cannot simplify such a complicated network using Star to Delta, Delta to Star Conversion. So, that is why the necessity of this Star to Delta and Delta to Star Conversion is to simplify the most complicated networks. This is the Star Network with RA, RB, RC. There one terminal is connected to get the neutral point as Ohm, whereas other terminal of all these three resistors connected to three other parts of the network. Star to Delta Conversion. Now, let us derive from Star Network to Delta Network. In Star Network, we are having resistance R1, R2, R3, whereas Delta, R1, R2, R3, R31. In the last video, we derived formula for Star resistances as R1 equals to R1 to R31 upon R1 to R2, R3 plus R31. Similarly, R2 will be equals to product of these two that is R12, R12, R23 upon summation of all Delta resistances that is R12 plus R23 plus R31. Similarly, this R3 will be equals to product of these two is equals to R23, R31 upon R12 plus R23 plus R31. Let us give this as equation number 1, this as 2 and this one as 3. Now, let us multiply 1 into 2, then add it to equation number multiplication 2 into 3. I can add it to equation number 3 into equation number 1. Now, let us multiply 1 and 2 will be getting R1, R2 is equals to R12 square R23, R31 summation of R12 plus R23 plus R31 bracket square. Similarly, multiplication of 2 and 3 will give R2 into R3 that will be equals to R23 bracket square R23 square into R12 R31 upon R12 plus R23 plus R31 bracket square. Multiplying 3 and 1, we will be getting R3 into R1 is equals to R31 square R12 R23 upon R12 plus R23 plus R31 bracket square. Let this be a equation number 4, this equation number 5 and this will be equation number 6. Now, add equation number 4, 5 and 6 will be getting R1, R2 plus R2, R3. That will be equals to R12 square R23 R31 plus R23 square R12 R31 plus R31 square R12 R23 divided by R12 plus R23 plus R31 bracket square. Now, taking R12 R23 R31 from each of these three terms, we will be getting R1 R2 plus R2 R3 plus R3 R1 is equals to R12 R23 R31 into bracket R12 plus R23 plus R31. Divided by R12 plus R23 plus R31 bracket square. So, here this term and this square will get cancelled. So, the remaining will be this in which we will be getting here R3 is equals to R23 R31. Now, if you look at this R23 R31 upon summation of delta resistance, you will be here R23 R31 upon summation of this is nothing but the R3 R1 R2 plus R2 R3 plus R3 R1 is equals to R12 into R3. So, I can write as rewrite as R12 is equals to R1 R1 plus R2 plus R1 R2 upon R3. So, this is the equation for delta resistance R12. Similarly, R23 will be equals to R2 plus R3 plus R2 R3 upon R1. R31 is equals to R3 plus R1 plus R3 R1 upon R2. So, in this way we got we derived a delta resistances from the star resistances. So, this is the exercise assignment convert this star into a delta network having resistances 5 ohm, 20 and 10 ohm. Remember converting from star to delta resistances this R12 R12 is coming over here this R12 will be equals to summation of these two resistances plus product of these two divided by opposite resistances. So, in this way R12 will be equals to 10 plus 5 plus 10 into 5 upon 20 that comes out to be 17.5. Similarly, R23 comes out to be 20 plus 5 plus 20 into 5 divided by 10 comes out to be 35. R31 is equals to 10 to be 20 plus 10 plus 20 into 10 divided by how it comes out to be 70 ohm. References, Textbook, Electrical Technology by B.L. Theraja. Thank you.