Find the resistance between terminals A and B in the electric circuit of Fig. 2.153 using Δ–Y transformation.
We convert the delta forming resistances between the terminals A, B, and C into an equivalent star. The resistances between the terminals A, B, and C and the star point N are R_{AN},\ R_{CN},\ and\ R_{DN}. These are calculated as
\begin{aligned} & \mathrm{R}_{\mathrm{AN}}=\frac{20 \times 30}{100}=6 \Omega \\ & \mathrm{R}_{\mathrm{CN}}=\frac{30 \times 50}{100}=15 \Omega \\ & \mathrm{R}_{\mathrm{DN}}=\frac{20 \times 50}{100}=10 \Omega \end{aligned}After transformation of the delta into star, the circuit becomes as shown in Fig. 2.154.
Total resistance, \mathrm{R}_{\mathrm{AB}}=6+\frac{60 \times 60}{120}
= 36 Ω