The impact of distributed generation on the Italian distribution network: upgrading of regulatory and technical rules in order to guarantee and improve reliability and efficiency of the electrical system

Abstract

The new scenario of the Italian electrical system is featured by the exponential growth of Distributed Energy Resources (DER), mostly PV, resulting in a deep change of network planning and operational criteria. Traditional load profiles on distribution network are changing, thus modifying the power plants operation and progressively introducing a new role for the DSO as energy flow manager in an active network, obviously in close coordination with the TSO. So, even for plants connected on LV and MV networks, it is necessary to manage the power of each generator, according to new requirements introduced by the Italian Regulator. Furthermore, the extension of the frequency range in which DER must stay connected to the electrical network, as recently established by Italian Regulator's Acts, has increased the difficulty on managing the high number of connections of DG plants to the distribution network, mainly on LV network, leading to potential unintentional islanding situations. Criteria are being developed in order to prevent this phenomenon, by means of innovative protections using new communication systems such as optical fibre in MV network and PLC systems in LV network. The inverter and its PWM control system are going to have a key role for DER management, and the Interface Protection Relay (IPR), controlled by inverter PWM, is going to drive the disconnection of static generators in case of exceeding frequency or voltage threshold, thus helping the DSO to avoid security problems. In order to cope with the new problems arising in the distribution network, the new Italian technical standards, introduced in 2012, specify the technical requirements that active users must respect to be connected. This paper shows, in the first part, some data related to the increase of DER on Enel Distribuzione's network, with the description of some typical issues that have recently arisen in the operation of the electrical network. The second part describes the developments resulting from the new technical standards for DER connections to the distribution network, the new strategies adopted by Enel Distribuzione and the innovative components and equipments which Enel Distribuzione is already installing to reach a better integration of DER, improving efficiency and reliability of the electrical system. (4 pages)