Suppression of the atmospheric over-voltages in grounding neutral conductor low-voltage grids

Abstract

This study reports the issues related to over-voltages in low-voltage distribution networks characterised by high specific soil resistance. A detailed description of real case observed on GSM Transmitter Glavica – Vrgorac is reported. The transmitter is supplied via the distribution cable from SS 10/0.4 kV/kV Podprolog. Since specific soil resistance and corresponding transmitter grounding resistance are quite high, over-voltages were flowing towards the substation grounding system via the cable neutral conductor, instead through the transmitter grounding system. In this case, authors applied an innovative approach. The solution is based on the theory considering the impulse grounding behaviour rather than the classical static response. Instead of modelling the horizontal grounding electrode as Ohmic resistance, the electrode capacitance and inductance are incorporated (adopted Telegrapher's equation). The following solution arisen: approximately in the middle, 100 m long part of the existing over-head cable was replaced by the buried cable. Instead of the neutral conductor from the cable (which was disconnected), non-insulated Cu wires (2 × 50 mm2) were applied. The novelty is in the application of a non-insulated neutral conductor as the lightning grounding. The validity of solution is verified via extensive in situ measurements.