# The Natural Load

The characteristic impedance Z_{0} (equation 3.7) is known as the surge impedance if the line is considered to be lossless and all resistances are neglected. When a line is terminated in its characteristic impedance the power delivered is known as the natural load. For a loss-free line supplying its natural load the reactive power absorbed by the line is equal to the reactive power generated, that is.

and

At this load, V and I are in phase all along the line and optimum transmission conditions are obtained. In practice, however, the load impedances are seldom in the order of Z_{0}. Values of Z_{0} for various line voltages are as follows (corresponding natural loads are shown in parentheses): 132 kV, 150 V (50 MW); 275 kV, 315 V (240 MW); 380 kV, 295 V (490 MW). The angle of the impedance varies between 0 and —15°. For underground cables Z_{0} is roughly one-tenth of the overhead-line value. Lines are operated above the natural loading, whereas cables operate below this loading.