K.L. Stricklett

Investigation of S/sub 2/F/sub 10/ production and mitigation in compressed SF/sub 6/-insulated power systems

The Cooperative Research and Development Agreement (CRADA), established to study the production and mitigation of S/sub 2/F/sub 10/ (disulfur decafluoride), one of a number of toxic by-products formed in electric discharges in the insulating gas SF/sub 6/, is described. The particular concern about S/sub 2/F/sub 10/ is due to its highly toxic nature, the ceiling limit value being 10 parts per billion (ppb, or 1 part in 10/sup 8/), and the need for development of sensitive detection techniques down to this level. In the presence of an electrical discharge such as an arc, spark, or corona, a portion of the SF/sub 6/ decomposes into lower fluorides of sulphur which can react to form a number of chemically active by-products including SOF/sub 2/ and SO/sub 2/F/sub 2/. During the maintenance or repair of SF/sub 6/-insulated equipment, the handling of these gaseous is a matter of concern. Preliminary arc experiment results, reported health-related incidents caused by SF/sub 6/ by-products, and ongoing studies are discussed.<<ETX>>

Early streamer emission lightning protection systems: An overview

Early streamer emission (ESE) lightning protection systems are a relatively new approach to the perennial problem of lightning damage, and these systems may hold promise for a more effective protection against lightning. However, the scientific and technical basis for this improved performance is far from certain and the efficacy of these technologies remains open to question. In this paper we examine the physical basis for ESE devices and identify areas of controversy and gaps in our knowledge of lightning and lightning protection that need to be considered in assessing ESE devices and in their future development.

Recent advances in partial discharge measurement capabilities at NIST

Three techniques for measuring the properties of partial discharges (PDs) are described. The first is concerned with an advanced, real-time PD measurement system that allows a complete characterization of the stochastic properties of PD. With this system it is possible to measure a set of conditional PD pulse-amplitude and pulse-time separation distributions from which memory effects characteristic of the discharge phenomena can be quantified and interpreted. Results for pulsating negative corona discharges in gases are shown. The second technique allows PD location in cables using time-domain reflectometry with appropriate statistical analysis. With the third technique, simultaneous measurements are made of the optical and electrical characteristics of PD in liquid dielectrics using fast photography combined with broadband. low-noise pulse current measurements. >

Dissociative electron attachment to S2F10, S2OF10, and S2O2F10

The absolute cross sections for dissociative electron attachment to the molecules S2F10, S2OF10, and S2O2F10 were measured in an electron transmission experiment. The corresponding negative‐ion fragments were identified in a separate mass spectrometric measurement. For S2F10, the attachment of thermal electrons (energy less than 0.1 eV) appears to result primarily in the formation of F− and SF5− with possibly a small fraction of SF4− and SF6−. The ions F− and SF5− are also produced from two attachment resonances at electron energies of about 4.5 and 9.5 eV. Both S2OF10 and S2O2F10 have unusually large dissociative attachment cross sections (on the order of 10−12 cm2) at energies near 0.1 eV. Electron attachment to S2OF10 yields primarily SOF5−, while S2O2F10 yields both SF5− and SOF5− with possible minor fractions of F− and SOF3−. Self‐consistent‐field calculations have been carried out on the neutral molecules and the corresponding anions to aid in the description of the observed dissociative attachment.

Phase behaviour in AC generated partial discharges: electro-convection and the moderation of discharges

Summary form only given, as follows. The temporal (phase) behaviour of partial discharges generated in transformer oil is examined. The system evaluated consists of a point-plane electrode gap energized by an ac potential oscillating at a frequency of 70 Hz; the experimental methods employed provide a complete phase-history of all discharge events. Analysis of these data show that the discharge events are highly correlated at short phase-separations, in that the likelihood of discharges with phase-separation 4//spl pi/ is greatly diminished and is in marked contrast with the behaviour predicted for random, independent events. We suggest that convective flow plays a predominant role in moderating the initiation of further discharges for a phase-separation of 4//spl pi/ under the described experimental conditions. The conditions for electro-convection and the characteristics of the fluid flow are discussed.

Appearance Potentials of Ions Produced by Electron-Impact Induced Dissociative Ionization of SF6, SF4, SF5Cl, S2F10, SO2, SO2F2, SOF2, and SOF4

The identification of S2F10, a highly toxic compound,1 in SF6 that has been subjected to electrical discharges, including negative corona discharges,2,3 sparks,4 and arcs,5 has raised issues of safety and proper handling of SF6 removed from electrical equipment, and motivates the need for trace detection of S2F10 in SF6. 6 A reliable measurement protocol for trace detection of S2F10 may be applied to: 1) develop safe handling procedures for SF6 gas removed from operating machinery, 2) ensure compliance with regulatory agencies, 3) monitor the purity of SF6 supplied both by manufacture and reprocessing, and 4) replace animal toxicity tests of commercial SF6.

Procedure for Measuring Trace Quantities of S2F10, S2OF10, and S2O2F10 in SF6 using a Gas Chromatograph-Mass Spectrometer

The compounds S2F10, S2OF10, and S2O2F10 are formed by decomposition of gaseous sulfur hexafluoride (SF6) in electrical discharges.1,2 The species S2F10 is known to be highly toxic to humans,3 and there is recent evidence that S2O2F10 may also be very toxic.4 There is, therefore, an interest in having analytical methods to detect these compounds in compressed SF6 at trace levels down to 10 parts in 109 by volume (10 ppb v ). Two Chromatographic methods have been used to detect these compounds at the 10 ppb v level or lower. The first method developed by Sauers and coworkers5 is based on a cryogenic enrichment procedure first proposed by Janssen,6 and uses a gas Chromatograph with an electron-capture detector. The second method, which is the focus of the present work, utilizes a gas chromatograph-mass spectrometer (GC/MS) with a thermal-chemical converter.7