The loadability of short transmission lines (less than \(25 \mathrm{~km}\), represented by including only series resistance and reactance) is determined by ________; that of medium lines (less than \(250 \mathrm{~km}\), represented by nominal \(\pi\) circuit) is determined by ________; and that of long lines (more than \(250 \mathrm{~km}\), represented by equivalent \(\pi\) circuit) is determined by ________.