Question

Why in a transmission line we generally use I2R formula, why V2/R formula is not used there???

Answer 1

These formulas are numerically the same, but I believe it depends on which numbers you are measuring. If you are measuring current, it is easier to use formula (1), but if you are measuring voltage, it would be better to use formula (2).

Answer 2

In a transmission line , the connections are in series. thus for calculating the power by V2/R voltage drop across the concerned device must be known but we know the current flowing through the device thus it is easier to use the other formula