Harmonic resonance overvoltage analysis in a mixed overhead line and underground cable in transmission systems

This paper deals with analyzing harmonic impedance and resonance overvoltage in the mixed overhead and underground cable lines of 220 kV transmission system in the Hanoi area. Underground cable length in combination with the change of system topology was found to have significant impact on the harmonic impedance at different 220 kV substations. The harmonic impedance is scanned over a wide range of frequency up to harmonics of 40
^th
order to identify parallel resonance of the mixed overhead line and underground cables system. The effect of cable length and system topology on the harmonic impedance is also studied in detail. A limited amount of harmonic current is injected into the system to observe the resulting resonance overvoltage in the bus with the highest resonant impedances. Simulation results suggest that surge arresters and equipment insulation in adjacent to the transition point between the underground cable and overhead line are particularly vulnerable to the harmonic resonance overvoltage.