Numerical Analysis of the Transient Overvoltages Caused by Single Phase Intermittent Arc Earth Fault in 35 kV Network with Isolated Neutral

The paper deals with the numerical calculations of transient overvoltages caused by the single phase intermittent arc earth fault in 35 kV network with isolated neutral. Numerical calculations are performed in the EMTP-ATP software, by using a model of the system whose accuracy is verified for this type of calculations. Sensitivity analysis is performed to investigate the impact of the parameters of the electric arc model on the calculated overvoltage waveshapes and amplitudes. Calculated overvoltage amplitudes are up to 3.45 p.u. Additional escalation of the overvoltage amplitude can be achieved if the interelectrode distance is continually increasing with the increase of the phase overvoltage amplitude. The harmonic content of the overvoltages waveshapes is calculated by using Fast Fourier Transform. The most pronounced are low order odd harmonics. They can be very high in faulted phase for low values of the arc ignition voltage.