Heatwaves and underground MV cable joints failures

In the last years, the summer meteorological conditions became much hotter and more arid as one of the consequences of the climate changes. These conditions have caused and are causing an increasing number of unexpected failures in underground medium voltage cables, mainly in correspondence of cable joints which are weak points of the system. The anomalous hot weather conditions during the summer period may last for several days (heatwaves), worsening appreciably the consequence of this phenomenon; the stress obviously increases as the number of the warmer days and lack of rain prolongs, heating cable and joint insulating materials with their internal defects and voids, wherein partial discharge phenomena may be easily triggered at this higher temperature under the action of the electrical field greatly increased in correspondence of such defects and voids. The present paper reports a study on the hotter day sequences in some Italian main cities with the aim to establish a correct definition for the term heatwave, to be used when dealing with underground cables failure topic.