From my understanding there are two causes for power losses in transmission lines:
Losses due to resistance:
\$ R = \frac{\rho l}{A} \$, where \$\rho\$ is the resistivity, \$A=\pi r^2\$ and \$ l \$ is the length of the cable.
Losses caused by the transformer, which again can be calculated or the transformer can be assumed to be ideal and to simply ignore the losses.
I assume that skin effect can be ignored in this case, as the frequency is relatively low (50Hz) and the diameter of the cables is not large.
Are there any other causes for power loss in transmission lines or are those the only two (or three as the transformer has core and copper losses)? If there are any other causes, how can they be calculated?