The influence of higher harmonics on transients during arcing earth faults in 6–10 kV cable networks with insulated neutral

Abstract

Alternating arc single-phase earth faults in 6–10 kV cable networks with insulated neutral are accompanied by over-voltages and a significant increase in the root-mean-square current value at the fault location. When evaluating the specified parameters of transient voltages and currents during arc earth faults, as a rule, the presence of higher harmonics in earth fault current is not taken into account. At the same time, in modern systems of industrial and urban electricity supply, the customers with nonlinear current-voltage characteristics are widely used. They caused a significant increase in the share of higher harmonics in earth fault currents of more than 40–55 % of the total network capacitive current determined at the fundamental frequency of 50 Hz. With such correlations between the levels of the fundamental frequency component and higher harmonics, higher harmonics can have a significant effect on the conditions of quenching and reignition of grounding arcs and, accordingly, on the parameters of transient voltages and currents in intermittent arc earth faults. Simulation in Matlab with SimPowerSystem was used to study the influence of higher harmonics in earth fault current on transient voltages and currents in 6–10 kV cable networks with insulated neutral. Modeling of alternating arc faults was carried out on the basis of existing theories of the occurrence of maximum overvoltages during arc earth faults in networks with isolated neutral developed by W. Petersen and Belyakov N.N. On the basis of computational experiments on simulation models of 6–10 kV cable networks with different values of the total capacitive current, it was shown that in the case of arc alternating earth faults the presence of higher harmonics in the earth fault current can lead to an increase in the multiplicity of overvoltages in intact phases by 13–16 % and the root-mean-square value of the current at the fault location by up to 22 %. Higher harmonics in earth fault current can have a significant effect on the conditions of extinction and reignition of the grounding arc, leading to an increase in the time of its extinction, the multiplicity of the maximum overvoltage level and root-mean-square value of fault current during alternating arc faults, which should be taken into account when evaluating the network efficiency in the isolated neutral mode.