Question

Power loss during transmission is calculated using the formula P=I²R but not using the formula P=VI.why?

Answer 1

When applying V²/R, remember the voltage you are referring to should be voltage drop across the line and NOT line to line voltage or line to ground voltage.

The voltage drop across the line at no load only depends upon current flowing and the line resistance. So when sending end voltage is increased the current in line goes down and so the voltage drop. So both formula can be used interchangeably but V should be V=(Vsending -Vreceiving) which is the drop across transmission line.

so Line voltage may not be used.

so we use the other equation.