Electrical Power System Essentials

5.5 CONTROL OF TRANSPORTED POWER

5.5.1 Controlling Active power Flows

Apart from the phase shifter, which is described hereafter, there are other options to control the active power flows in the system. When HVDC-links are part of the grid, see also Section 1.3.1 (AC versus DC systems), the active power flowing through the DC links can be influenced; this is an additional advantage of HVDC-links. Another piece of equipment that is able to control active power flows is the Unified power-Flow Controller (UpFC); as this device can serve other purposes as well it is treated separately in Section 5.5.3 (Unified power-Flow Controller (UpFC)).

Figure 5.19 Principle layout of a STATCOM.

The phase shifter

The phase shifter or phase-shifting transformer is shown in Figure 5.21. The windings drawn in parallel to each other are on the same iron core and are magnetically coupled. Therefore, a tapped winding is on the same magnetic core as the winding whose voltage is 90 degrees out of phase with the line-to-neutral voltage that is connected to the center of the tapped winding:

Figure 5.20 Reactive power exchange between the STATCOM and the grid.

Figure 5.21 The phase shifter [10].

The result ...