Novel insulation materials for high voltage cable systems

Abstract

IntroductionCross-linked polyethylene (XLPE) has replaced oil-paper insulated systems as the primary solution for medium and high voltage ac cables decades ago, since they enable marginally higher operating temperatures and can be produced with high throughput and well-controlled extrusion technology [1]. The base for this insulation is polyethylene (PE), which can be crosslinked either with peroxide cure (involving thermal decomposition), or by grafting silane onto the polymer chains, and the use of moisture based cure [2]. Crosslinking is deemed necessary, since commercially available, branched low density polyethylene (LDPE) has more significant melting at temperatures around 100 ºC and the material loses all of its mechanical stability. In contrast, linear high density PE (HDPE) has a higher melting point and can achieve higher operating temperatures. But while HPDE found some success in medium voltage cables, it has not managed to establish a foothold in the high voltage cable sector [3]. After decades of research, conventional XLPE is at the limit of its capabilities, as outlined below, and further development is bound to have diminishing returns. Further, the costs of large extrusion and catenary crosslinking manufacturing facilities and the costs and time of degassing larger cross-section HV and EHV cables present significant sustainability issues for cable manufacturers.

The role of the filler surface chemistry on the dielectric and thermal properties of polypropylene aluminium nitride nanocomposites

“…Regarding the application of PP-based materials, it is considered to be a great potential for recyclable HVDC cable insulations [7,16]. However, the poor thermal conductivity of PP impedes the PP cable to reach higher operating temperature [16].…”

“…Regarding the application of PP-based materials, it is considered to be a great potential for recyclable HVDC cable insulations [7,16]. However, the poor thermal conductivity of PP impedes the PP cable to reach higher operating temperature [16]. Many studies show that high thermal conductive nanoparticles, such as aluminium nitride (AlN) and boron nitride (BN), can improve the thermal conductivity of the matrix material [7,8,17].…”

Space Charge and Breakdown Strength Behaviour of PP/POE/MgO Nanocomposites

“…As an important developing direction of smart grids, HV technology lays the groundwork for the ongoing trend of long distance, ultra-high voltage direct current transmission [1]. Cables play an important role in HV transmission, and electrical insulation is a crucial factor in limiting cable development [2]. Cross-linked polyethene (XLPE), the current state of the art in cable insulation material, has some limitation in terms of dielectric and thermal characteristics, as well as the lack of recyclability.…”

“…Cross-linked polyethene (XLPE), the current state of the art in cable insulation material, has some limitation in terms of dielectric and thermal characteristics, as well as the lack of recyclability. Even in "ultra-pure" XLPE, impurities produced during the industrial production process is inevitable [2,3]. Hence, PP as a recyclable and eco-friendly material was coming into the view of researchers.…”

“…Hence, PP as a recyclable and eco-friendly material was coming into the view of researchers. Compared to PE, PP has comparable electrical properties such as electrical breakdown strength, but better performance on inhibiting space charge and a higher melting temperature, which is more than 160 [2]. Due to its thermoplastic nature, PP can be recycled and reshaped [3].…”