Smart links for distribution networks: The right way to further integrate renewables

Abstract

Distribution systems, and more specifically medium voltage (MV) networks, have not reached the automation level and technological sophistication of transmission systems. In fact, the introduction of the smart grid concept simply recognizes the urgent need and opportunity to improve the performance of distribution networks, in view of the new challenges they are facing nowadays. MV systems, being structurally meshed, are however radially operated. Until recently, the absence of any generation at this level has invariably led energy to flow from the substation to distribution transformers. This significantly simplifies both the operation of these systems and the design of the protection equipment. Owing to the need of assuring back-up supply, radial feeders are customarily oversized so that they can serve, at least partially, the load of neighboring feeders in case of fault. In this context, the growing presence of dispersed generation (DG) is, on the one hand, reducing the spare feeder capacity, leading in many cases to congestions, and, on the other, complicating the operation and protection schemes. The use of power electronic devices is seen as a promising way of enhancing both asset utilization and massive DG penetration, much in the same way HVDC systems were introduced decades ago at the transmission level. More specifically, in this work smart links between MV feeders and tap changers for distribution transformers, both based on electronic devices, are considered and assessed on actual distribution systems. These devices are sized and placed during a preliminary planning stage in order to maximize the dispersed generation that can be accommodated and/or the system loadability. Then, during the operational stage, the associated control variables are scheduled according to a new optimization problem intended to balance the load among bridged feeders or to minimize power losses. A simplified economic assessment is also included in order to prove that these smart devices can be a profitable investment, not only for utilities but also for the owners of DG.