Power Flow Control and Power Swing Damping

One of the major advantages of series compensation is that through its use real power flow over transmission corridors can be effectively controlled. Consider, for example, the SMIB system shown in Fig. 10.17 in which the generator and infinite bus are connected through a double circuit transmission line, labeled line-1 and line-2. Of the two transmission lines, line-2 is compensated by a series compensator. The compensator then can be utilized to regulate power flow over the entire system.

Fig. 10.16 Power-angle and line current-angle characteristics of the two different methods of voltage injection: solid line showing constant reactance mode and dashed line showing constant voltage mode.

For example, let us consider that the system is operating in the steady state delivering a power of  P_m0 at a load angle of δ₀ . Lines 1 and 2 are then sending power P_e1 and P_e2 respectively, such that P_m0 = P_e1 + P_e2 . The mechanical power input suddenly goes up to P_m1 . There are two ways of controlling the power in this situation:

• Regulating Control: Channeling the increase in power through line-1. In this case the series compensator maintains the power flow over line-2 at P_e2 . The load angle in this case goes up in sympathy with the increase in P_e1 .
• Tracking Control: Channeling the increase in power through line-2. In this case the series compensator helps in maintaining the power flow over line-1 at P_e1 while holding the load angle to δ₀ .

Let us illustrate these two aspects with the help of a numerical example.

Example 10.4