Page 210 - Basic Electrical Engineering

Thus, when-star-connected resistances are changed to equivalent delta-
forming resistances, the values are

Remembering of these expressions is easy as R is the sum of R and R 2
1
12
plus product of R and R divided by the third resistor, i.e., R . (i.e., delta-
3
2
1
equivalent resistance of one side is the sum of touching resistances plus
product of the touching resistance dividing by the non-touching resistance).

Now let us solve a few problems of network simplification using star–delta
transformation and series–parallel calculations.

Example 2.36 Calculate the equivalent resistance of the network across

terminals P and Q.

Figure 2.124

Solution:

Two 6 Ω resistors are in parallel. Their equivalent resistance is 3 Ω. So the
circuit is redrawn as shown in Fig. 2.125. By pulling point Q downwords this