Fullerenes are shown to be efficient voltage-stabilizers for polyethylene, i.e., additives that increase the dielectric strength of the insulation material. Such compounds are highly sought-after because their use in power-cable insulation may considerably enhance the transmission efficiency of tomorrow's power grids. On a molal basis, fullerenes are the most efficient voltage stabilizers reported to date.

A new application area for fullerenes: voltage stabilizers for power cable insulation.

The development of electrical insulation is closely associated with the development of electrical apparatus. Up to about 1925 only naturally occurring products such as asphalt, rubber, mica, cotton thread or fabric were generally used. Mineral oil-impregnated paper was used in transformers, capacitors, and underground cables at voltages up to 69 kV [1]. Then the first synthetic insulating materials, namely phenolic (Bakelite®) and alkyd (saturated polyester) resins, were used in insulating varnishes. Polyvinylchloride was introduced in 1936 to replace natural rubber in underground cable and house wiring, but in spite of tremendous advances in compounding polyvinylchloride to improve its properties, the electrical losses could not be reduced sufficiently. It was restricted to LV applications up to a few kilovolts. A variety of synthetic elastomers was used to replace natural rubber for HV applications, e.g., butyl rubber in the 1940s and ethylene-propylene rubber later on. Epoxy and polyester resins became available around 1945 and were first used for molding and encapsulation of electronic components, then mostly in laminated form as electrical insulation for LV applications [2]. Increased knowledge of the chemistry of insulating materials, and improved processing, then led to the availability of a large number of plastic materials such as polyethylene terephthalate, polycarbonate, polystyrene, low- and high-density polyethylene, polypropylene, polytetrafluoroethylene and fluorinated ethylene-propylene copolymer, suitable in thin film form for capacitor applications. These thin films could work at high electrical stresses or, put more practically, at minimal dielectric thickness appropriate to the capacitor working voltage. Thin films (<;10 μm) of these materials have intrinsic electric strengths in the range 500 to 1,100 V/μm at room temperature, probably 2 to 10 times higher than the average breakdown strength of plastic-film capacitors at the time [3]. Polyethylene-insulated of electrical energy, a statement that is still valid today and certainly will remain valid in the future. The objective of this paper is to give an overview of the research carried out over the last 50 years that has contributed to the development of high-field polymer dielectric materials in a broad sense. During this time thermoplastic polymers have been used in a large variety of electrical systems, e.g., cables, capacitors, transformers, bushings, electrical machines, and accessories operating in a large variety of environments (space, nuclear, thermal, etc.). Progress has been highly nonlinear in time, entangled with progress in material sciences, our understanding of the electrical properties of insulating polymers, and advances in material processing. We emphasize what are, in our view, the main features.

Advances in high-field insulating polymeric materials over the past 50 years

The synthesis and physico-chemical properties of seven benzil-type voltage stabilizers are reported. The benzil core is substituted with alkyl chains of different length that are linked to the benzil core via an ester, ether, or tertiary amine group. All additives can be melt-processed with low-density polyethylene (LDPE). Fourier-transform infrared spectroscopy confirms that benzil compounds are not affected by the LDPE cross-linking reaction induced by dicumyl peroxide. Moreover, a combination of gel content measurements, thermal analysis, and small-angle X-ray scattering indicates that the presence of benzil voltage stabilizers does not significantly alter the microstructure of cross-linked polyethylene (XLPE). Electrical tree inhibition experiments under high-voltage alternating current conditions show that all investigated additives substantially enhance the dielectric strength of the insulating material at a concentration of only 10 mmol kg−1. The highest improvement in dielectric strength, of more than 70% with respect to reference XLPE, is obtained with voltage stabilizers, which carry short (methyl) side chains that are linked to the benzil core via an ester or tertiary amine group.

Tailored side‐chain architecture of benzil voltage stabilizers for enhanced dielectric strength of cross‐linked polyethylene

Thioxanthone derivatives as stabilizers against electrical breakdown in cross-linked polyethylene for high voltage cable applications

The invention relates to a use of a polymer composition for producing an insulation layer of an AC power cable with and to an AC cable surrounded by at least an insulating layer comprising daid polymer composition.

Polymer composition and a power cable comprising the polymer composition

Quantum mechanical criteria for choosing appropriate voltage stabilization additives for polyethylene

Power cables that comprise a sheath layer, e.g., an insulation layer, are produced from a mixture of a high pressure polyolefin free of silane functionality, e.g., high pressure low density polyethylene, and a polyether polyol of which at least 50 percent of its molecules comprise no more than a single hydroxyl functionality. Preferably, the power cable is a medium or high voltage power cable, and the polyolefin is crosslinked as the sheath layer is fabricated and/or subsequent to the fabrication of the sheath layer.

Low dielectric loss power cable sheaths comprising high pressure polyolefins free of silane functionality

The present disclosure is directed to a plasticizer composition, polymeric compositions containing the plasticizer composition, and conductors coated with the polymeric composition The plasticizer composition includes a first plasticizer comprising epoxidized fatty acid alkyl esters and a second plasticizer comprising an epoxidized natural oil The plasticizer composition, first plasticizer, and/or second plasticizer can undergo one or more color-reducing treatment processes, such as distillation, filtration, and/or peroxide treatment

Plasticizer compositions and methods for making plasticizer compositions

Methods and compositions for controlling polymer crosslinking are provided. The crosslinking composition includes a crosslinkable polymer, a free radical initiator, and an amine. The amine is an alkoxyaminc or a hydroxylamine. The crosslinking composition is heated to a processing temperature. The amine undergoes a cleavage reaction at or below the processor temperature to produce nitroxyl radicals in situ . The tree radical initiator forms polymer radicals at the processing temperature. The nitroxyl radicals formed in situ cap the polymer radicals to control crosslinking.

Method for inhibiting scorch in crosslinkable compositions

L'invention concerne un procede de preparation d'une matiere composite durcie utile pour des applications de filtre radiofrequence, consistant a : (a) se procurer une composition de resine epoxy thermodurcie durcissable comprenant (i) au moins une resine epoxy; (ii) au moins un agent de durcissement; (iii) au moins un durcisseur; et (iv) au moins une charge; (b) faire durcir la composition de resine epoxy thermodurcie durcissable de l'etape (a) pour former un composite durci, dans lequel la composition de resine epoxy thermodurcie durcissable lors du durcissement fournit un produit composite durci ayant un equilibre de proprietes comprenant Tg, un coefficient de dilatation thermique, une resistance a la traction, une conductivite thermique; et ayant une masse volumique de moins de 2,7 g/cm 3 ; et (c) revetir au moins une partie de la surface du composite durci de l'etape (b) par une couche de metal conductrice de l'electricite pour former un revetement metallise sur au moins une partie de la surface du compose durci. La matiere composite durcie peut etre utile comme boitier de corps de filtre a cavite radiofrequence pour des applications de filtre radiofrequence.

Robert F. Eaton

Papers

Quantum mechanical criteria for choosing appropriate voltage stabilization additives for polyethylene

Low dielectric loss power cable sheaths comprising high pressure polyolefins free of silane functionality

Plasticizer compositions and methods for making plasticizer compositions

Method for inhibiting scorch in crosslinkable compositions

Composites de résine époxy