Performance and refurbishment strategies for protection systems according to new quality requirements from energy authority, Enel DK5600 connection requirements and change of neutral earthing of MV distribution networks in Italy

The Italian MV distribution networks are undergoing a significant transformation, driven by the Electrical Energy Authority (AEEG). Within his statutory objectives of enhancing the quality and performances of the Italian distribution network, the Authority published in 2004 an integrated quality regulation. It defines a quality of supply regulatory mechanism based on penalties to the utilities underperforming and on automatic reimbursements to worst quality affected customers. It promotes through customer´s reimbursements/penalties the renewal process of the customer´s interconnection plants and protection systems to ensure higher protection selectivity levels for customer site faults and therefore to limit not localised interruptions affecting the distribution networks. In this scenario Enel Distribuzione, the major Italian utility with over 92.000 MV customers, is pursuing an extended program of connecting to ground the MV neutral point to all his MV networks within 2007, to achieve substantial reduction of supply interruptions due to faults and, consequently, to meet the Authority quality targets. In March 2004 Enel issued a new version of his DK5600 MV network interconnection rules, stating the technical requirements of the customer´s interconnection plants and protection systems to match the new network neutral management. In the paper the new scenario is briefly described, analysing the technical and economical aspects driving the utility requirements on one side and the impact and needs of customers on the other side. The focus will be major novelty items of DK5600 requirements, i.e. on the connection switchgear and protection system, on the impact on new plants and refurbishment of existing ones. The extended dynamic range and the accuracy required under normal and fault conditions according to DK5600, both for current and voltage transducers, for the protection device and the whole protection system are analysed and commented together with the operation- l condition they arise from. The adoption of non-conventional current and voltage transducers now accepted by Enel and some experimental characteristics of the linearity, accuracy and saturation behaviour of such transducers are then described, comparing the performances with conventional protection current transformers. In conclusion the impact on existing customer plants of the new regulations and the protection system refurbishment options are highlighted.