engleski

Influence of neutral grounding on overvoltages in distribution network

The paper describes the comprehensive study of the overvoltages generated by faults in the transmission distribution electrical network. The research comprised over 500 live tests of the single phase-to-earth fault in the 10 kV network of the city Pula in Croatia. The great increase of cable lengths in the network, required grounding of the neutral point in the supply substation 35/10 kV in order to limit the single phase-to-earth currents. The study was conducted with the aim to determine the impact of the neutral point grounding resistance on overvoltages in the network. Different values of the resistor were used. Moreover the networks with the insulated neutral point were tested. Overvoltages were studied in three different configurations of the cable network. The cable lengths of small, medium and large network were 7 km, 22 km and 53 km respectively. The computer model of the cable network and the supply station was additionally developed and simulations were conducted with Electromagnetic Transient Program (EMTP). The measurements were compared with results obtained with EMTP program. Both, shapes and the maximal overvoltage values measured in the tests match well the EMTP results. The conclusion can be reached, that the overvoltage factors are reduced to relatively low values, mostly below the value of a double phase peak voltage, if the neutral point of the network 10(20) kV is grounded through the resistor. This is under a condition that the nominal resistor current is three times greater than the earth fault capacity current.

overvoltages; distribution network; single phase-to-earth fault; neutral point grounding resistance.

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