Crosslinked polyethylene (XLPE) is a key material used for power cable insulation due to its electrical properties and structure. It is most commonly made by taking the polymer low-density polyethylene (LDPE) and crosslinking its branches together using the chemical agent dicumyl peroxide (DCP). Understanding the dielectric properties and electrical conductivity of XLPE is critical due to its widespread use. However, there is large variation in the observed conductivity parameters of XLPE. For example, the reported activation energy of conduction can be as low as 0.4 eV and as high as 2 eV, despite similar preparation. It has been shown that the Meyer-Neldel rule applies to DC conduction within XLPE, which constrains the activation energy to have an exponential relationship with the pre-exponential factor. Recent evidence showing that this relationship also applies to AC conductivity obtained using broadband dielectric spectroscopy will be discussed in this talk.<br/><br/>After carrying out basic electrical characterization such as quantifying the effects of DCP concentration and crosslinking temperature, the dielectric loss was measured in a group of XLPE samples that were all processed in the same manner at a variety of temperatures and frequencies. The dielectric losses were converted into values of AC conductivity, from which the activation energy and pre-exponential factor were extracted. In these samples it was found that the compensation law was obeyed without a corresponding isokinetic point in the conductivity versus temperature plot, similar to the case of DC conduction. LDPE samples were also examined for comparative purposes, and it was found that the two are similar in terms of the range of activation energies measured. Furthermore, compensation was suppressed in XLPE samples that were not degassed and were instead exposed to water. Thus, electrical compensation was found to play a major role in the conductivity of polyethylene.

Exploring the compensation law in the conductivity of polyethylene via dielectric spectroscopy

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