The impacts of degassing on space charge characteristics and DC conductivity in semicon-bonded XLPE for HVDC cable applications

Abstract

-High voltage direct current (HVDC) cables are one of the key components for the HVDC power transmission system. HVDC cables for higher voltage level, larger power capacity and higher reliability are still desired for the power industry as part of a global power strategy. One of the major concerns related to HVDC applications is the presence of space charge within the dielectrics, which distorts the electric field distribution and contributes to accelerated ageing and consequent failure of the cable insulation. The byproducts generated from the crosslinking process during the manufacture of XLPE insulation for HVDC cable are one of the major sources of hetero-charge formation in dielectrics. Therefore, degassing is widely applied in cable manufacture for the removal of such crosslinking byproducts. In this paper, composite XLPE samples were produced that include two layers of semiconductive polymer (semicon), which are thermally bonded on the top and bottom of the XLPE insulation, to mimic a real cable manufacturing process. The samples were degassed under vacuum and elevated temperature for 1, 3 and 6 days and their space charge characteristics and conductivities were then measured at an applied field of 40 kV/mm. The influence of the degassing period and the semicon material formulation on space charge formation and distribution in the system are discussed and the findings are compared with undegassed samples.

Space Charge Measurement and Modelling in Cross-Linked Polyethylene

“…Furthermore, a concentration gradient of impurities in the thick insulation layer of cables should be also taken into account. In addition to these, the properties of the semicon/insulation interface plays a major role in charge injection and accumulation, as the contained impurities may diffuse into the bulk, assisting the formation of hetero charges [34]. One restriction of this initial model is that only one type of impurity which can be dissociated into positive and negative ions is considered, and the concentration level of the impurity is assumed to distribute uniformly in the XLPE.…”

“…Furthermore, a concentration gradient of impurities in the thick insulation layer of cables should be also taken into account. In addition to these, the properties of the semicon/insulation interface plays a major role in charge injection and accumulation, as the contained impurities may diffuse into the bulk, assisting the formation of hetero charges [34].…”

Investigation on effect of semiconducting screen on space charge behaviour of polypropylene‐based polymers for HVDC cables

“…Although the well-developed XLPE is still predominant in HVDC cables owing to its superior thermo-mechanical and electrical stability and robustness, one major concern arises from the impurities and by-products introduced during crosslinking, which is considered as the main contribution of space charge accumulation in the XLPE cable. Degassing can effectively remove some of the impurities, but the process requests long-term high-temperature treatment which is timeconsuming and costly [22,23]. More importantly, the thermosetting nature of XLPE makes it nonrecyclable and not sustainable.…”

Space charges analysis on insulator with uniform layer contamination effect

“…Technology in HVDC transmission has managed many industrialists in the world to invest polymer in direct current (DC) on power cables. Polymeric insulation such XLPE is the most commonly used and best insulator in features [1][2][3][4][5][6][7][8], when used with DC operation may inconsistently lead to a problem. Space charge inside the insulated material increased due to the lowest carrier mobility and high trapped rate in certain states, increased the space charge through the body of the insulated material.…”