Suppression of the atmospheric over-voltages in grounding neutral conductor low voltage grids
Abstract
This paper reports the issues related to over- voltages in low-voltage distribution networks characterized by high specific soil resistance. Detailed description of real case observed on GSM Transmitter Glavica – Vrgorac is reported. Transmitter is supplied via 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 substation grounding system via cable neutral conductor, instead through transmitter grounding system. In this case, authors applied innovative approach. The solution is based on the theory considering the impulse grounding behavior rather than the classical static response. Instead of modelling horizontal grounding electrode as Ohmic resistance, electrode capacitance and inductance are incorporated (adopted Telegrapher’s equation). Following solution arisen: approximately in the middle, 100 m long part of the existing over-head cable was replaced by buried cable. Instead of neutral conductor from the cable (which was disconnected), non-insulated Cu wires (2x 50 mm²) were applied. The novelty is in the application of non-insulated neutral conductor as the lightning grounding. Validity of solution is verified via extensive in-situ measurements.
