An Efficient Procedure to Identify and Quantify New Molecules for Insulating Gas Mixtures

• Published in: Contributions to plasma physics (1988) Vol. 54; no. 1; pp. 3 - 13
• Main Authors: Franck, C. M., Dahl, D. A., Rabie, M., Haefliger, P., Koch, M.
• Format: Journal Article
• Language: English
• Published: Berlin WILEY-VCH Verlag 01-01-2014; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Automation; Electric potential; Electrodes; Gas mixtures; High Voltage Insulation; High voltages; Insulation; Mathematical models; Pulsed Townsend discharge; SF6 replacements; swarm parameters; Voltage
• ISSN: 0863-1042; 1521-3986
• DOI: 10.1002/ctpp.201300030

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)