...Contd...An Alternate Method of Voltage Injection

The power-angle characteristics of this particular series connection are given in Fig. 10.15. In this figure the base power is chosen as V²/X . Three curves are shown, of which the curve P₀ is the power-angle curve when the line is not compensated. Curves which have maximum powers greater than the base power pertain to capacitive mode of operation. On the other hand, all curves the inductive mode of operation will have maximum values less than 1. For example, in Fig. 10.15, the curve P₁ is for capacitive mode and the curve P₂ is for inductive mode of operation.

Fig. 10.15 Power-angle characteristics for constant voltage mode.

The reactive power supplied by the compensator in this case will be

(10.30)

Improving Stability Margin

From the power-angle curves of Figs. 10.13 and 10.15 it can be seen that the same amount of power can be transmitted over a capacitive compensated line at a lower load angle than an uncompensated system. Furthermore, an increase in the height in the power-angle curve means that a larger amount of decelerating area is available for a compensated system. Thus improvement in stability margin for a capacitive series compensated system over an uncompensated system is obvious.