electrical grid

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.

Medium voltage distribution power grids mostly operate with ungrounded neutral points of transformers. The philosophy of these electrical grids is based on the assumption that they are more reliable than grids with grounded neutral. However, transient currents during single phase or multiple faults to ground, depending mostly on the phase to ground capacitances of the used cables connected to power grid substation buses, frequently have intermittent nature due to arising arc.