Ageing, Space Charge and Nanodielectrics: Ten Things We Don't Know About Dielectrics

Abstract

Three areas of considerable progress are identified in the area of polymeric insulation since the mid 1990s (i.e. since the inception of the Eric O. Forster Memorial Lectures): the understanding of ageing, the measurement of space charge, and the development of nanodielectrics. The paper proposes a typology to distinguish and define electrical ageing, degradation and breakdown. With reference to the principal theories of thermo-ageing, it is concluded that there is little direct evidence for ageing even though it is likely to exist, at least above a critical field. The capability to measure space charge has improved considerably and this shows considerable potential as a diagnostic tool. Space charge behaviour is extremely difficult to analyse and general predictions may be impossible in practice. It is, however, necessary to control space charge accumulation in HVDC systems. Nanodielectrics continue to offer promise and understanding is improving in this area, particularly in the development of models of interaction zones around nanoparticles.

Polyethylene-Based Dielectric Composites Containing Polyhedral Oligomeric SilSesquioxanes Obtained by Ball Milling

“…Nanodielectrics, defined as composites containing nanofillers (i.e., fillers with at least one dimension less than 100 nm) embedded in a dielectric matrix (e.g., a polymer), have great potential for serving this purpose as they can present superior dielectric properties compared to conventional dielectrics and dielectric microcomposites [4][5][6][7][8][9][10][11]. XLPE-based nanodielectrics containing silica nanoparticles can present improvements in several key dielectric properties over neat XLPE, such as increased dielectric breakdown strength, enhanced voltage endurance, enhanced partial-discharge resistance and reduced space charge accumulation [12][13][14][15][16].…”

Short-term breakdown and long-term failure in nanodielectrics: a review

“…It starts from a void in macroscopic scale somewhere in dielectric. The process is very fast (<< 1 s) at only one location, then the dielectric could not be used anymore [18].…”

“…Under a variety of field stresses, the breakdown suffered by dielectric material presents a very strong time-dependent relationship, so it can be divided into five or more kinds by breakdown speed as shown in Table 1 [18]. The three formers are known as the short-term breakdown, the others are degradation [19][20].…”

Effect of Silane Coupling Agent Chemistry on Electrical Breakdown Across Hybrid Organic–Inorganic Insulating Films

“…Strong hydrogen bonding between the silica surface silanols and silicone oil has been noted previously, but the silicone oil likely exists as a partial monolayer on the surface as the excess has been washed off in a good solvent. 37 'Spike' breakdown, because of its sudden, high slope, is estimated by the authors to possess greater electronic character than the other I-V types because of its abrupt nature relative to thermal processes; 10,38 however, given the limited time resolution of our experiments, conclusive evidence of this character is not presented. The complex nature of the 'Spike-Ohmic' and 'Discharge' I-V types probably consist of both electronic and thermal breakdown mechanisms operating simultaneously, although 'Discharge' may also represent other pre-breakdown phenomena, such as those associated with avalanche quenching.…”