Evaluation of fault levels and power supply network impedances in 230/400V 50Hz generic distribution systems

In this paper, typical strengths, fault levels and source impedances are thoroughly analysed and calculated for the study of quality of supply in 230/400V 50Hz distribution systems. Considering all the disparity in distribution network design, this study is based on a comprehensive database containing typical arrangements and equipment in UK/European systems, as well as on fully documented generic network models supplying four residential load subsectors in the UK, i.e. from metropolitan to rural areas. Thus, this paper proposes an alternative method for determining reference values of network supply impedances and short-circuit fault levels at different points and locations of the medium-to-low voltage distribution system. The aim of this study is to provide a wider range of benchmark values than those stipulated in the IEC 60725 Standard, which only defines a single-reference threshold of public supply impedances for all types of distribution systems and residential customers. In order to assist network operators in the planning and design of their distribution systems, these values are further disaggregated and classified in this paper according to network/demand type.