No abstract

No abstract

Poly(4‐methyl‐1‐pentene) (P4MP) was characterized to evaluate its viability as a high‐temperature dielectric film for capacitors. Detailed investigation of thermal, mechanical, rheological, and dielectric properties was carried out to assess its high‐temperature performance and processability. P4MP was melt‐processable below 270 °C without degradation and application temperatures as high as 160–190 °C can be achieved. The dielectric constant and loss of melt‐processed P4MP films was comparable to biaxially oriented polypropylene (BOPP) capacitor films, although the dielectric strength was lower. Enhancements in dielectric strength up to 250–300% were achieved via solution‐processing P4MP films, which could be easily scaled up on a roll‐to‐roll platform to yield isotropic, free‐standing films as thin as 3–5 μm. The influence of crystal structure, crystallinity, and surface morphology of these films on the dielectric properties was examined. The dielectric strength was further increased by 450% through biaxial stretching of solution‐cast films, and a Weibull breakdown field of 514 V/μm was obtained. The dielectric constant was very stable as a function of frequency and temperature and the dielectric loss was restricted to <1–2%. Overall, these results suggest that BOP4MP is a promising candidate to obtain similar energy density as a BOPP capacitor film but at much higher operating temperatures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1497–1515

Fundamental studies of potential candidates for DC electric power transmission in high temperature environment, including ETFE, FEP, PTFE, PI and PEEK, are carried out and presented in form of the series papers containing space charge and conduction as part I, partial discharge as part II, and the degradation and surface breakdown as part III. In this part, the space charge at 20kV/mm was measured at 25 °C and with a thermal gradient at 50 °C. The electrical conductivity was measured at electric fields ranging from 10kV/mm to 30kV/mm in temperatures ranging from 25 °C to 200 °C. The experimental results showed that considering the effect of thermal condition and electric field, FEP has the lowest total amount of space charge accumulation and electric field distortion among these materials at the measured conditions. PI and PEEK have the lowest amount of trap-controlled mobility at 25 °C due to deeper average trap level because of the aromatic rings in the structure. PTFE and PI have the lowest amount of thermal activation energy and temperature-dependent electrical conductivity due to the more uniform morphological phase comparing to ETFE, FEP, and PEEK. The outcomes of this paper serve as a benchmark for the fundamental researches over high temperature materials for DC applications and lay a basis for Part II and Part III.

silicone rubber coating applied to insulators in rd located near Long Island Sound has depolymerized and become putty-like after six years of service. Coating samples were taken from high creep insulators which were energized and weathered, weathered but not energized, and neither weathered or energized (warehouse storage). The unweathered and unenergized coating did not appear to degrade. The weathered but unenergized coating had degraded measurably but was still in an operational state. The energized and weathered coating has become putty-line and lost all physical integrity. This suggests aging by a combination of chemical, photochemical (weathering), and electrochemical mechanisms.

Analysis using Gas Chromatography/Mass Spectroscopy (GC/MS) was performed for evaluation of surface degradation of silicone insulating materials. Silicones are used as coatings for porcelain insulators and shed material for high voltage composite insulators. A comparison between virgin silicone rubber and aged silicone rubber samples, which were aged either on actual power lines or during a field exposure test, was made by GC/MS analysis. The GC/MS spectrum of siloxane in silicone rubber has a series of peaks which corresponds to the number of dimethylsiloxane units in the molecule. We found that the aged samples had a larger concentration of low molecular weight siloxane species than the virgin samples. The top shed surfaces generated more low molecular weight siloxane species than the bottom shed surfaces. Since GC/MS analysis can determine the molecular weight distribution of polymer insulating materials, evaluation of the degree of surface degradation and estimation of the remaining life of insulators may be possible.

Plasma–solid interaction represents a major concern in many applications such as power-interruption and plasma–metal processing. Characterized by high-current density and voltage drop, the arc roots dissipate intensive heat to electrode vaporization, which participates in the ionization and, thereby, significantly alters the plasma properties and gas dynamics. Most of the arc root models feature approaches based on surface temperature or (temperature dependent) current density. Due to the complexity of conjugated heat transfer across arc roots involving three-phase interactions of plasma with liquid spots and solid electrodes, accurately determining the surface temperature distribution is extremely computationally demanding. Hence, models hitherto fail to quantitatively estimate neither the molten spot size nor the total amount of vaporization. In this work, we propose an arc root model featuring a hemispherical structure that correlates the molten spot size with the heat partition between conduction and vaporization to estimate the energy dissipation at arc roots and, thus, to trace the vaporization rate. Following local partial pressure adjusted Langmuir vaporization, we deduce an analytical solution of molten spot size for quasi-steady-state, which compares favorably with experiments. Specifically, the vaporization dominates over conduction for large molten spots as in the case of high-current arcs. However, for low-current arcs, the vaporization heat is trivial compared with conduction. Furthermore, we integrate this arc root model into a study case of arc plasma based on the magnetohydrodynamics method. The simulated arc voltage and arc displacement match with the experiment. This model is expected to find broad applications in power interruption and plasma etching.

No abstract