Towards an uniform MV system earthing in EDP distribuição — Project challenges and QoS improvements

EDP Distribuição (EDP Group), is the mainland Portugal Distribution System Operator (DSO), with more than 6 million customers, over 400 HV/MV Substations, 60 thousand MV/LV Substations, 80 thousand km Network (HV/MV) and a LV Network about 140 thousand km. At the end of 2010, most of the substations had low impedance earthing at the MV level, although there was a set of substations, mainly located in the centre of the country, which were operated in isolated neutral. Between 2009 and 2010 several pilot projects were conducted by EDP Distribuição to evaluate the benefits of the MV impedance earthing vs. isolated neutral. The outcome of those projects confirmed a reduction in the number of outages and a Quality of Service improvement, as presented in Cired 2011 paper 0853 [1]. So, EDP Distribuição decided to launch a nationwide program to achieve an uniform MV neutral earthing system. The rollout of the Earthing Standardization Program was launched at the end of 2010, and was finished at the end of 2012. The aim of this paper is to show how EDP Distribuição successfully achieved the purposes of the program, dealing with several constraints, and the resulting Quality of Service (QoS) improvement.