Network interconnection studies of distributed generation

The structure and control methods of existing distribution networks are designed based on the assumption of unidirectional power flows. The amount of generating units connected to distribution networks is, however, constantly increasing which changes the operation of distribution networks in many ways. The directions of power flows and fault currents may be altered and the passive distribution networks become more active. This change in distribution network operation has to be taken into account also in network planning stage which, in turn, creates a need to develop the network planning tools and procedure. In countries where the electricity market is deregulated the distribution network operator (DNO) is obligated to connect distributed generation (DG) into its network. The DNO has little power on the characteristics of the DG unit (location, size, network connection type) and conducts the interconnection studies based on the data obtained from the potential energy producer. This paper discusses the interconnection studies required when a new DG unit is to be connected to an existing distribution network. The effect of DG on distribution network planning is discussed and development needs for present network planning tools are proposed.