Search

The partial discharge inception voltage (PDIV) of low-voltage induction motor turn-turn insulation analogy is investigated for variable relative humidity (RH) of the surrounding air (temperature and pressure are kept constant close to their ambient values). Three materials, perfluoralkoxy alkane, sealed and unsealed alumina (UA), are employed as the dielectric coating (insulation) of test samples. Each material's dielectric properties change differently with RH—of these, relative permittivity is regarded as the most crucial, as it was previously proven to be, along with the coating's thickness, the key factor in determining the PDIV in dry air conditions. To further vary the value of permittivity and thus provide larger data sets for the verification study, the frequency of the excitation voltage is also varied between 1 Hz and 50 kHz. The obtained experimental data are compared against the PDIV predictions obtained by a breakdown model based on the reduced thickness of the coating (ratio of the coating thickness to its relative permittivity). Satisfying agreement between the measured and predicted PDIV are obtained for the first two materials, whereas significant discrepancies are seen for the UA material. For this case, surface conductivity is introduced into the prediction model and much better fits to the experimental data are obtained for a suitable value of surface resistance. It is hence demonstrated that the model is able to satisfactorily predict the PDIV for three substantially different materials when the RH of the surrounding air is varied between 10 % – 80 % . [ABSTRACT FROM AUTHOR]

A positive synergy in the electric strength was observed in a previous study in SF6/HFO1234ze(E) mixtures which was shown to result from a strong electron energy moderation capability of HFO1234ze(E) combined with thermal electron attachment of SF6 (Egüz et al 2022 J. Phys. D: Appl. Phys. 55 315203). In the present work, the electron energy moderation properties of compounds with a similar C=C−C backbone are investigated. Swarm and breakdown measurements are performed in pure gases and in mixtures with SF6. Compounds with a trifluoromethyl group (−CF3) showed lower characteristic energy and as a consequence a positive synergism with SF6. Descriptors related to electron energy moderation are identified and computed; a clear trend is found from the analysis of descriptors related to inelastic processes which suggest(s) that vibrational excitations may be the main source of electron energy loss in the compounds showing positive synergy. [ABSTRACT FROM AUTHOR]

We probe the electron attachment in hexafluoropropylene oxide (HFPO), C3F6O, a gas widely used in plasma technologies. We determine the absolute electron attachment cross section using two completely different experimental approaches: (i) a crossed-beam experiment at single collision conditions (local pressures of 5 × 10−4 mbar) and (ii) a pulsed Townsend experiment at pressures of 20–100 mbar. In the latter method, the cross sections are unfolded from the electron attachment rate coefficients. The cross sections derived independently by the two methods are in very good agreement. We additionally discuss the dissociative electron attachment fragmentation patterns and their role in the radical production in industrial HFPO plasmas. [ABSTRACT FROM AUTHOR]

Copyright of B&H Electrical Engineering is the property of Sciendo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this contribution, a new procedure to systematically identify and quantify novel molecular gases with low global warming potential for application in high voltage insulation as gas mixtures is presented. The attention is focused on highly efficient procedures to be able to scan a large number of candidate gases. To identify new molecules, we derived an empirical correlation between the electric strength of a gas and certain molecular properties, like polarizability or dipole moment, which can be calculated by means of density functional theory. The swarm parameters of these pre-selected molecules in mixtures with buffer gases is then quantified, using a newly set-up Pulsed Townsend experiment. The setup operates with a high degree of automation to enable systematic evaluation of gas mixtures not to miss possible synergistic effects. Key element of this PT setup is a new photocathode that works with a high quantum efficiency and long lifetime even when exposed to reactive species during the measurements. Moreover, for an automated operation it is important to know precisely in which range the experiment can be operated, i.e. for example to know up to which electron density space charge effects can be neglected. Finally, the measured swarm parameters need to be translated into breakdown voltage strengths of different electrode arrangements and different applied voltage wave shapes. For this, a model of the the streamer to leader transition in SF6 will be applied to other strong electronegative gases in future studies to test if the model is universally valid. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]