Impulse withstand voltage of single-phase compact distribution line structures considering bare and XPLE-covered cables

This paper is dedicated to investigate the impulse withstand voltage of single-phase compact distribution line structures of 15 kV class. The structures are tested in laboratory with the application of standard lightning impulse waveforms of positive polarity. Three situations are considered: (i) XLPE-covered cables with brand new insulation; (ii) XLPE-covered cables with punctured insulation; (iii) bare cables, aiming at assessing the critical case in which the insulating layer of the cable is completely deteriorated. The results indicate that the presence of an XLPE layer covering the cable leads to a significant increase in the impulse withstand voltage of the investigated structures compared to the use of bare cables. In the cases considering brand new XLPE-covered cables, insulation breakdown leads to the formation of a pinhole in the insulating layer at points up to about 200 cm from the tested structure. The presence of pinholes in the tested cable specimens has no significant effect in the breakdown voltage of the tested structures, except when the pinhole is sufficiently close to the pole. Finally, to provide elements for investigating the performance of the structures when subjected to nonstandard impulse voltages, parameters for volt-time curves and for the disruptive effect (DE) method are provided for the critical case of structures with bare cables.