The impact of neutral treatment and earth fault protection on resiliance and reliability of high voltage grid

Since EdF in France and Enel in Italy changed the neutral treatment in their power distribution grids to resonance grounding in the late nineties, this kind of grounding has become popular again in Europe. Both companies reported large improvements of their SAIDI and SAIFI figures short after the switch to resonance grounding.Resonance grounding has been used in Swedish and German power grids right after Waldemar Petersen's invention of the arc suppression coil in 1917. More recent safety regulations in Sweden stipulate mandatory fault detection up to 20kOhm. This led to the development of a new protection algorithm at the Royal Institute of Technology in Stockholm in the late eighties.The new protection scheme - zero sequence admittance differential - provides not only safe detection of high impedance earth faults, but also the tools to improve the fault current compensation of the Petersen coil. With practically no voltage injection and fault current left at the fault site in less than three cycles, the new “GFN Ground Fault Neutralizer” finally brings a substantial improvement for public safety and fire prevention.The latter problem is of particular interest in countries like Australia and California with considerable bushfire problems cause by undetected line fracture faults. A recent press release of the government in Victoria/Australia (7) claims a forty percent reduction on bushfires after installation of “Rapid Earth Fault Current Limiters”. Facing similar climate conditions in the Mediterranean parts of Europe the new GFN now offers a way to reduce the increasing risk for devastating bush- and forest fires.A second field of application for the new Ground Fault Neutralizer is for cable grids. For the first time arcing cable faults are quickly stopped without power interruption. But cable faults are generally not transient. Sooner or later the faulty cable must be disconnected for repair. Therefor a more important aspect on cable protection is the possibility to detect faulty cables long before they develop a full insulation breakdown. Here the GFN offers a new powerful tool for the early detection of cable PD.