Long-term electrical performance and life model fitting of XLPE and EPR insulated cables

Abstract

In the paper the results of life tests performed on XLPE and EPR cable models are presented and discussed. The performances of the two insulating niaterials when subjected to electrical stress are compared on the basis of characteristic parameters derived by the best-fitting life models. It is found that while EPR is well described by linear models, XLPE data fit curvilinear life models, showing tendency to electrical threshold. Hence the fundamental parameter for XLPE characterization is the threshold value, while the voltage endurance coefficent should be used to characterize EPR. Considerations on test and data-processing metodologies, as well as insulation design, point out the criteria to be used for the two models.

Electron spin resonance spectral study of PVC and XLPE insulation materials and their life time analysis

“…This chemical change confirms physical changes, in general plastic degradation, which favors treeing inception and growth up to breakdown when voltage is applied [26,27]. Fig.…”

A comparative investigation of electrothermal endurance models for insulating materials and systems characterization

“…does not yet find enough experimental support (formation of microcavities was detected, but was not correlated to (10)). Model (10) was checked fitting breakdown data taken from life tests performed on XLPE cable models, presented in [9], but it is unlikely that this model can hold, if not as a phenomenological expression, for both tree induction and growth periods, which determine the failure time of the tested cables.…”

“…The advantages of eq. ( 3 ) with respect to (10) are, however, the broader validity, the respect of the boundary conditions (1) (which does not hold for (lo), where L(E,T)+L(E) for T=O [27]), and the fact that its temperature dependence is thoroughly expressed. Moreover, eq.…”

“…In this way, a thermodynamic support has been established for both the linear and the threshold models, which derives from ( 3 ) , so that a physical background is identified for these models as for model (10). The advantages of eq.…”

“…According to the above-mentioned model, it can be realized that the experimentally observed behavior of insulating materials, that is, either linear or curvilinear, depends on the ratio between service or test stresses and threshold values [8,[16][17][18][19][20], so that high values of this ratio (as occurs for ethylene-propylene rubber, EPIC [4,103) lead to work with linear models, while low values allow the threshold to be detected [6,10,20]. The mathematical formulation of the general model is:…”