These equations are plotted as a function of δ in Fig. 1,
with the voltages and the line reactance equal to 1 pu.
The active power is proportional to the voltages on the
sending and the receiving side and to the sine of the electrical
angle between both sides; it is also inversely proportional to
the line reactance. Altering the active power can be done
by altering the voltages, but this has a bigger influence on
the reactive power, so this method is not very effective.
The total line reactance can be lowered by placing a series
capacitor in order to compensate for the inductance of the line.
Besides the increased power flow, an additional advantage of
this method is that oscillations can be damped by switching
the capacitor at appropriate times. Some Flexible Alternating
Current Transmission Systems (FACTS) can alter the total line
impedance very dynamically [5], [6], [7].