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Innovation in distribution grid with ungrounded neutral, RedNA


MV distribution grid of the companies Gas Natural Fenosa (UFD) and E.On uses a configuration with ungrounded neutral (that is a transformer neutral that is not connected to ground). Unlike the configuration with grounded neutral, this one has the fundamental advantage of having not high short-circuit currents for ground fault and it ensures the continuity of service during the fault. Nevertheless, it has some disadvantages and it is expected to research on products that manage to overcome them.

This project started in 2011 and it concluded in 2015. It is led by Gas Natural Fenosa and participating companies are E.On, ZIV Grid, ZIV Comms, Ingeteam, General Electric, the Universidad de Sevilla and the Instituto Tecnológico de la Energía.


The aim of the project is to develop technological solutions that lead to the improvement of the operation of grids with ungrounded neutral, and that are important for the improvement of the electricity supply quality and the automation of this kind of distribution grid (Smart Grid) in an economically feasible way. Solutions include:

  • Sign of distance to the fault in MV grids
  • Fault detection in MV grids with ungrounded neutral
  • Fault detection in MV grids with ground fault neutralizer
  • Sensors and connection of carrier wave signal in MV
  • Algorithm of optimal service restoration in control center
  • Algorithm for optimal position of fault detectors


In 2014, ITE concluded the development of the following application software:

  • Service restoring software.

After the detection of a fault in a grid line or node, this application permits to propose the optimal reconfiguration of its topology in order to isolate the fault and restore the service.

  • Optimal position of fault detectors software.

This application localizes the points of the grid where fault detectors must be installed, optimizing their quality with economic criteria (power not supplied vs. equipment costs).

  • Fault localization software.

It permits to combine the fault detection information provided by the protections to localize the point of the grid where the fault was detected. This is exactly the information needed (together with the grid status and topology) by the service restoring application.

At the same time, within the project, pilot tests have been carried out for protections developed by different partners on MV grids in Toranzo-Luena (Cantabria), Mera (A Coruña) and Illescas (Toledo).