I. Sauers

Electrical properties of epoxy resin based nano-composites

We investigate the electrical properties of composite materials prepared as nano- and sub-micron-scale metal-oxide particles embedded in a commercial resin. The filler particles are barium titanate and calcium copper titanate. The physical and structural characteristics of the constituents and the fabricated composites are reported. Electrical characterization of the composite samples is performed using time- and frequency-domain dielectric spectroscopy techniques. The electrical breakdown strength of samples with nano- and sub-micron-sized particles have better electrical insulation properties than the unfilled resin.

Electron attachment to the perfluoroalkanes n‐CNF2N+2 (N=1–6) and i‐C4F10 a)

Parent and fragment negative ion formation from seven perfluoroalkanes [n‐CNF2N+2 (N=1–6) and i‐C4F10] under low‐energy (0–10 eV) electron impact has been studied using a time‐of‐flight mass spectrometer. For CF4, C2E6, and C3F8 only fragment anions were observed, F− being the most abundant. For n‐C4F10 a weak parent ion was observed, but again the predominant ion was F−. For i‐C4F10, n‐C5F12, and n‐C6F14 the parent negative ions were the most abundant with relative cross sections peaking at 0.6 eV and autodetachment lifetimes from 10 to 100 μs depending on the molecular size and electron energy. In addition to the parent negative ion and the F− ion, fragment negative ions of the form CNF−2N+1, CNF−2N, CNF−2N−1 (with N=1–6) have been detected. The relative cross sections for all observed negative ions have been measured and corrected for the finite width of the electron pulse using an unfolding procedure. The positions of the dissociating negative ion states (NISs) shift to lower energies with increasing ...

Enhancement of dielectric strength in nanocomposites

In this paper, we report the dielectric breakdown properties of a nanocomposite, a potential electrical insulation material for cryogenic high voltage applications. The material is composed of a high molecular weight polyvinyl alcohol and nanosized in situ synthesized titanate particles. The dielectric breakdown strengths of the filled material samples, measured in liquid nitrogen, indicate a significant increase in their strengths as compared to unfilled polyvinyl alcohol. We conclude that nanometre-sized particles can be adopted as a voltage stabilization additive.

Detection of 2-mercaptoethanol using gold-coated micromachined cantilevers

Abstract We have measured the response of gold-coated silicon nitride microcantilevers to 2-mercaptoethanol (HS–CH 2 –CH 2 –OH) vapors and found that they respond rather sensitively to 2-mercaptoethanol vapors. Such microcantilevers can be used to develop sensitive micromechanical chemical sensors for detecting sulfur-containing compounds. Microcantilevers with a gold coating on one side respond to adsorption of molecules by changes in their resonance frequency and/or bending. The bending induced from adsorption of 2-mercaptoethanol molecules on microcantilevers is at least an order of magnitude more sensitive than any corresponding resonance frequency changes resulting from mass loading. In the present studies, we used the adsorption-induced bending and placed a lower limit in the minimum detectable concentration of mercaptan vapor at

On dielectric breakdown statistics

In this paper, we investigate the dielectric breakdown data of some insulating materials and focus on the applicability of the two- and three-parameter Weibull distributions. A new distribution function is also proposed. In order to assess the model distributions trustworthiness, we employ the Monte Carlo technique and, randomly selecting data-subsets from the whole dielectric breakdown data, determine whether the selected probability functions accurately describe the breakdown data. The utility and strength of the proposed expression are illustrated distinctly by the numerical procedure. The proposed expression is shown to be a valuable alternative to the Weibull ones.

Triaxial HTS Cable for the AEP Bixby Project

Ultera has installed a single 200-meter long high temperature superconducting (HTS) 3-phase triaxial design cable at the American electric power (AEP) Bixby substation in Columbus, Ohio. The cable connects a 138/13.2 kV transformer to the distribution switchgear serving seven outgoing circuits. It was designed to carry 3000 Arms. Testing of 3- to 5-meter length prototype cables, including a 5-meter prototype with full scale terminations tested at ORNL was conducted prior to the manufacture and installation of the AEP triaxial cable. These prototypes were used to demonstrate the crucial operating conditions including steady state operation at the 3000 Arms design current, high voltage operation, high voltage withstand and 110 kV impulse, and overcurrent fault capability. A summary of the results from the thermal analysis and testing conducted by Ultera and ORNL will be presented. Some analysis of the cable thermal-hydraulic response based on the testing that were used to determine some of the cable cryogenic system requirements are also presented.

Recent Advances in Gaseous Dielectrics at Oak Ridge National Laboratory

Recent developments in gaseous dielectrics are discussed with emphasis on dielectric gas mixtures containing SF6. Recent findings on the isotopic, pressure, and nonuniform field dependence of the dielectric strength of gases are also presented, and ways to enhance the corona-stabilization characteristics of gas mixtures by appropriate additives (e.g. to SF6) are outlined. In addition, results are presented on the spark decomposition products of SF6 and the alleviation of the harmful effects of conducting particles by particle coating in situ. Finally, electron attachment, electron drift velocity, and breakdown properties of gas mixtures (e.g. C2F6 or C3F8 in Ar or CH4) - comprised of electron attaching and electron conductivity enhancing components - which have promise for use in pulsed power technologies are reported.

Gas phase hydrolysis of sulfur tetrafluoride: A comparison of the gaseous and liquid phase rate constants

The second‐order gas phase reaction rate constant for SF4 hydrolysis to SOF2 has been determined by mass spectrometry and found to be in the range (0.9–2.6)×10−19 cm3 s−1 at 350 K. The hydrolysis of SOF2 in the gas phase is 3 to 4 orders of magnitude slower than that of SF4. Since only liquid phase rate constant data exist for SF4 and none for SOF2, our gas phase rate constant for SF4 was extrapolated to liquid H2O density for comparison to the literature and was found to be consistent with the rate constant for complete aqueous hydrolysis of SF4, which was indirectly determined by the conductivity change in a pulse radiolysis study of SF6 in aqueous solution. The agreement between these values provides direct support for the conclusion of the pulse radiolysis study, namely, that the rate‐determining step involves water attack on SF4. The present data further indicate that SOF2 cannot be an intermediate in the aqueous hydrolysis of SF4. A reaction is proposed for both gaseous and liquid phase hydrolyses w...

Gas‐phase hydrolysis of SOF2 and SOF4

The rates for gas‐phase hydrolysis of SOF2 (thionylfluoride) and SOF4 (thionyl tetrafluoride) have been measured at a temperature of 298 K. The second order rate constant for SOF2 hydrolysis in SF6 buffer gas was found to have the value (1.2±0.3)×10−23 cm3/s which agrees with previous estimates of Sauers et al., but is three orders of magnitude lower than the value obtained by Ruegsegger et al. at 340 K. The rate constant for SOF4 hydrolysis has not previously been measured and its value in both SF6 and N2 buffer gases was found here to be (1.0±0.3)×10−21 cm3/s.

By-product formation in spark breakdown of SF6/O2 mixtures

The yields of SOF4, SO2F2, SOF2, and SO2 have been measured as a function of O2 content in SF6/O2 mixtures, following spark discharges. All experiments were made at a spark energy of 8.7 J/spark, a total pressure of 133 kPa, and for O2 additions of 0, 1, 2, 5, 10, and 20% to SF6. Even for the case of no added O2, trace amounts of O2 and H2O result in the formation of the above by-products. However, addition of O2 significantly increases the yields of SOF4 and SO2F2, while SOF2 is only slightly affected. The net yields for SOF4 and SO2F2 formation range from 0.18×10−9 and 0.64×10−10 mol·J−1, respectively, at 1% O2 content to 10.45×10−9 and 7.15×10−10 mol·J−1, respectively, at 20% O2 content. The mechanism for SOF4 production appears to involve SF4, an important initial product of SF6, as a precursor. Comparison of the SOF4 and SO2F2 yield from spark discharges (arc and corona) shows that the yields from other discharges (arc and corona) shows that the yields can vary by at least three orders of magnitude, depending on the type of discharge and on other discharge parameters.