Conference Agenda

Bis(trifluoromethyl) sulfides, i.e., CF3SCF3, was proposed to be a potential alternative to refrigerant fluids. Moreover, the significant attachment cross section of low-energy electrons for CF3SCF3 is to make it good gaseous dielectrics and also good electronegative gas for the electrical applications. CF3SCF3 has high uniform field breakdown strength 1.35 times that of sulfur hexafluoride (SF6), a potent greenhouse gas being phased out of all frivolous applications due to environmental concern. The global warming potential (GWP) of CF3SCF3 was estimated to be 2.8 by an empirical structure-reactivity relationship and thus CF3SCF3 has been designated to be a potential eco-friendly replacement gas for SF6. However, such an empirical estimation on the GWP of CF3SCF3 is highly problematic because the models trained with alkanes, alkenes, and thioethers might be inapplicable to the fluorinated compounds. Based on the solid ab initio quantum chemistry calculations on the reactions of CF3SCF3 and CH3SCH3 with OH radicals in the atmosphere, it is revealed that the reactivity of CF3SCF3 is completely different from CH3SCH3 in terms of both degradation mechanisms and kinetic behavior. Besides the absence of hydrogen abstraction mechanism, CF3SCF3 reacts with OH through the shallow wells (0.7 kcal/mol) rather than the stable complex (9.1 kcal/mol for CH3SCH3), forming the less stable tri-coordinated S(III) covalent intermediates before the endothermic S-C bond fission. The room-temperature rate coefficient for the CF3SCF3+OH reaction is four orders of magnitude lower than that for the CH3SCH3+OH reaction. The atmospheric loss of CF3SCF3 has been retarded considerably with a lifetime around 300 years. Together with the significant radiative efficiency, 0.463 Wm-2ppb-1, the GWP of CF3SCF3 is predicted to be approximately 14000, as indicative of a super greenhouse gas. The present work not only reveals the significance of fluorination effect on the reactivity of thioethers but also realizes that the empirical structure-activity models without the mechanistic insights should be taken with caution.

This paper provides an overview on stringent requirements for stator windings that are used in petrochemical, utilities and nuclear plants. For nuclear applications, it is critical that a machine must be designed for a Design Basis Accident (DBA) refers to a specific accident scenario that a plant design must consider and prepare for, such as a Loss Of Coolant Accident (LOCA) and built to withstand without loss to the systems, structures, and components necessary to ensure public health and safety. Stator winding insulation system can be quite complex due to the interactions of materials and geometry; therefore, testing is the most appropriate method for qualification. To carry out qualification tests for motor or motor stator winding insulation system, IEEE Std. 323 & 334 along with several other industry standards were followed. In addition to other qualifications tests and to achieve environmental qualification, a test program was performed on statorettes with two distinct types of insulation systems. The qualification program comprised of voltage aging, radiation aging, thermal aging, mechanical vibration aging, seismic testing and a DBA. The statorettes used as test specimens successfully completed the required qualification program and met the specified acceptance criteria. The integrity of the insulation system demonstrated that the motor stator will perform its safety related function when subjected to a DBA at the end of its service life. The qualified insulation system has been widely used in services industry with outstanding thermal, electrical and dielectric performance.

The demand for medium voltage direct current (MVDC) systems is rising as they enable lighter, more efficient electric ships and aircraft. However, medium voltage levels generate high electric fields that challenge insulation system reliability. In high voltage systems, the presence of triple points, sharp edges, bubbles, and air gaps can intensify electric fields, leading to partial discharge (PD) and space charge injection and accumulation within insulation materials. PD accelerates insulation aging and raises the risk of system-wide failures, while space charge causes electric field distortions, insulation degradation, and early device failure. Our recent findings suggest that incorporating electrets between electrodes and insulating materials effectively mitigates PD, space charge injection, accumulation, and space charge-induced breakdown of insulating materials. Electrets, materials with embedded positive or negative charges, generate electric fields that counter harmful fields created by system voltage, thereby blocking charge injection into insulators.

This study further explores the charge stability of electrets under high temperatures, varying electret thickness, and charging duration during fabrication. We fabricated electrets using Parylene HT through triode corona charging and measured embedded charge with an electrostatic voltmeter. To assess high-temperature effects, we placed electrets on a hot plate and monitored the normalized surface potential for over 30 hours. The effect of thickness on charge retention was analyzed by varying material thickness, fabricating samples, and measuring their normalized surface potentials. Additionally, we examined the impact of extended charging duration at high temperatures on electret charge stability during the fabrication process.