Abstract
This paper presents the results of a first investigation on the effects of lightning stroke on medium voltage installations’ grounding systems, interconnected with the metal shields of the Medium Voltage (MV) distribution grid cables or with bare buried copper ropes. The study enables us to evaluate the distribution of the lightning current among interconnected ground electrodes in order to estimate if the interconnection, usually created to reduce ground potential rise during a single-line-to-ground fault, can give place to dangerous situations far from the installation hit by the lightning stroke. Four different case studies of direct lightning stroke are presented and discussed: (1) two secondary substations interconnected by the cables’ shields; (2) two secondary substations interconnected by a bare buried conductor; (3) a high voltage/medium voltage station connected with a secondary substation by the medium voltage cables’ shields; (4) a high voltage/medium voltage station connected with a secondary substation by a bare buried conductor. The results of the simulations show that a higher peak-lowering action on the lighting-stroke current occurs due to the use of bare conductors as interconnection elements in comparison to the cables’ shields.
Highlights
The study enables us to evaluate the distribution of the lightning current among interconnected ground electrodes in order to estimate if the interconnection, usually created to reduce ground potential rise during a single-line-to-ground fault, can give place to dangerous situations far from the installation hit by the lightning stroke
When a direct lightning stroke injects the HV/Medium Voltage (MV) station, the majority of the current is injected into the soil by the station grounding system, whose lower ground resistance creates a preferential path for the leakage current
Even though MV cables’ metal shields have a small cross-section, they provide a significant path to the lightning current, towards close electrical installations; the current flowing through the metal shields is influenced both by the distance between the grounding systems and by the soil resistivity
Summary
The effects of lightning discharge currents in electrical installations and in grounding systems have been extensively investigated in the scientific literature [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. The distribution of lightning current among various interconnected ground electrodes is a very important issue to be investigated To this aim, our paper presents the results of a first investigation on the effects of lightning strokes on MV installations’ grounding systems, connected together with the metal shields of the MV distribution grid cables or with bare buried copper ropes. The study investigates the distribution of the lightning current among the interconnected ground electrodes in order to assess if the interconnection, normally established to reduce 1LtG faults current and the consequent GPR amplitudes, can give rise to dangerous situations far from the installation hit by a direct lightning stroke. The remainder of the paper is structured as it follows: Section 2 describes the mathematical approach used for simulating the interconnected ground electrodes injected by the direct lightning stroke; Section 3 reports the four above-listed application examples; Section 4, contains the conclusion of the work and a description of the future research
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