**AC Resistance and DC Resistance Relation:**

Though the contribution of line resistance to series line impedance can be neglected in most cases, it is the main source of line power loss. Thus while considering transmission line economy, the presence of line resistance must be considered. The effective AC resistance is given by

Where

- I is the rms current in the conductor in amperes.

Ohmic or DC resistance is given by the formula

where

- ρ = resistivity of the conductor, ohm-m
- l = length, m
- A = cross-sectional area, m
^{2}

The effective resistances given by Eq. (2.48) is equal to the DC resistances of the conductor given by Eq. (2.49) only if the current distribution is uniform throughout the conductor.

For small changes in temperature, the resistances increases with temperature in accordance with the relationship

where

- R = resistances at temperature 0°C
- α
_{0}= temperature coefficient of the conductor at 0°C

Equation (2.50) can be used to find the resistance R_{t2} at a temperature t_{2}, if resistance R_{t1} at temperature t_{1} is known