Высокочастотные коммутационные перенапряжения в сети среднего напряжения

Abstract

Conditions under which high-frequency impulse overvoltages occur in medium-voltage (MV) networks with insulated and resistively grounded neutrals are considered. It has been shown from numerical analysis results that voltage resonance may occur at high frequencies. In that case, the overvoltages may reach ten times the nominal voltage value. Owing to the use of arc chutes, resistively grounded neutrals, and metal-oxide surge arresters, the failure rate in MV networks has been decreased; however, faults due to high frequency overvoltages still have not been eliminated. Results from experimental investigation of impulse voltage distribution along the transformer winding are presented. The results of full-scale and simulation experiments have confirmed the possibility of resonance to occur at the medium-voltage level in carrying out switching operations at the high-voltage level. Under the conditions of high-frequency overvoltages, metal-oxide surge arresters are able to protect a limited area. A digital recorder equipped with contactless voltage sensors has been developed for recording high-frequency overvoltages. The overvoltages excited by switching operations at a 10 kV substation have been recorded.