Control of Underload-Tap Changing Transformer

In this paper, a new control logic for slow switching devices on the interconnected electric power systems such as underload-tap changing (ULTC) transformers and capacitor banks is proposed. The "misoperation" of these devices and the coordination problems of their control are associated with the recent reports on system-wide ill-conditioned operation in lower voltage ranges. The newly proposed control logic overcomes these problems and provides a means to regulate voltages within a desired threshold. First, the present practice in controlling the swiching devices is briefly reviewed. Next, new design is proposed and illustrated on examples.