Steady-state assessment of the DG impact on voltage control and loss allocation

The introduction of distributed generation (DG) affects the operational characteristics of the distribution systems. The impact depends on the level of penetration of DG, as well as on the possibility of operating significant portions of the distribution system as micro-grids, or to allow temporary operation of intentional islands. In the electrical sector, the major changes occurred in the last two decades led to modify the structure of the electricity business from a vertically integrated utility (VIU) system, in which the four major functions of the electrical chain (that is, generation, transmission, distribution and retail) were operated by the same company, to an unbundled system in which these functions are separated and are performed by different companies. One of the main effects of unbundling has been the decoupling of the function of generator with respect to the one of the distribution network operator (DNO). A plurality of local generators connected to the today’s distribution systems are owned and managed independently of the DNO. The objectives themselves at the local generation site management may differ from the ones of the DNO. More specifically: at the local generation site, the main goals are to provide energy to the local users, to sell excess electricity to the grid when the electricity price makes it convenient, and to reduce the internal losses; the DNO’s main objectives are to run the distribution system in a reliable, safe and secure way, without exceeding the operational limits on voltages and currents, maintaining reduced losses and satisfactorily high power quality levels; emerging options include the role of energy service companies or organised consortia in managing local generators located at different points in the networks in an integrated way, mainly for economic purposes, or the comprehensive management of portions of the networks with generators and loads as micro-grids.