The aim of this activity is to identify correlations between diagnostic parameters and the increased fault rate of self-shrinking joints in underground medium-voltage (MV) power lines, with the goal of improving service quality and reliability for users. This work follows last year’s testing on a custom-built circuit at the “MV Cable Diagnostics” laboratory. In addition to previously conducted measurement campaigns, three new ones are added to validate the methodologies used so far, to determine potential degradation dynamics of insulating systems. The results confirm a correlation between conductor temperature and critical thermal conditions, which are further emphasized by ongoing climate changes. The choice to adopt different measurement methodologies (continuous and off-line monitoring) has proven correct. In particular, on-line measurements have allowed for monitoring and highlighting the onset and extinction of localized degradation phenomena in XLPE-insulated cable segments, both during heating and cooling phases.

Dielectric spectroscopy of the insulating system provides a Tanδ curve that reduces false evaluations derived solely from point values acquired at 50Hz and 0.1Hz; moreover, this methodology detects degradation phenomena earlier than traditional techniques. Conducting Tanδ analysis with a hot conductor reveals phenomena that may appear mild or masked at ambient temperature. The test facility has enabled preliminary experiments on new transmission techniques that will likely play a role in managing the Internet of Things in the future.

Although soil moisture has not yet been considered, it can be stated that:

Some joints, under applied voltage and similar load conditions, reach operating temperatures beyond the limits imposed by the technology.
Innovative tests provide complementary information to traditional methods and are more sensitive to the manifestation of degenerative effects.
On-line monitoring allows for earlier acquisition of information about degradation causes compared to off-line methods.
The results suggest the need to acquire and analyze on-line diagnostic parameters with simulated load during component qualification tests.
Currently, in Italy, among transmission technologies, only NBiOT on licensed frequencies and Lora on unlicensed frequencies can be applied to low-cost sensors for monitoring underground MV power lines.
In the future, to better correlate laboratory results with the operating environmental conditions of buried MV cables, integration of information from the installed cables, which is currently not available, will be necessary.