isolated neutral

Distribution networks with a voltage of 35 kV are mostly used to supply electricity consumers located in rural areas. These networks, which mainly have overhead lines, normally function according to the radial principle, although in most cases they are closed or with two-way power. In recent years, the structure of 35 kV electric network has been changing, they are being transformed from aerial to aerial- cable due to the construction of 35 kV cable lines in rural areas, which in most cases are performed with cables with cross-linked polyethylene insulation.

The arc overvoltages during the single phase to earth faults in electrical distribution grids of 6-35 kV are the object of the research in this paper. The development of 35 kV distribution electrical grids is accompanied by the construction of new overhead and cable power lines. It causes a change of the capacitive earth fault current in the grids and also affects the multiplicity of overvoltages in electrical distribution grids during the single phase to earth faults.

The object of research is the choice of the optimal technical solution to prevent the development or the long existence of ferroresonance processes in electrical distribution grids of 6-35 kV, which are operated in isolated neutral mode. A lot of factors such as the grounding mode of a grid neutral, its capacitive current of a short circuit to the ground, the type and number of voltage transformers (VT) etc. influence on the probability of occurrence and duration of ferroresonance processes.

On the basis of computer simulation researched the influence of the grounding conditions of neutral of electrical network 35 kV on the level of arc, commutation, ferorezonansni overvoltage. Shown that the values of arc overvoltage and character development ferorezonans processes is significantly affected mode neutral grounding network. There were given schematic dependencies of arc overvoltage multiplicities which depend on the nature of combustion of grounding arc, grid configuration and the conditions of neutral grounding.