Thin Teflon-FEP capacitors with open-tubular channels employed on low-pressure measurements for smart-grid monitoring systems

In order to improve quality and efficiency in electrical energy distribution, power supply companies have sought for better ways to monitor their equipment, stimulating research in smart-grid projects. Equipment subjected to constant monitoring are power and distribution transformers, in which severe faults can be avoided through preventive maintenance, such as, detecting partial discharges in early stages, conducting oil chemical analysis or monitoring transformer internal pressure. In the present contribution we discuss the use of thin voided capacitors made of fluoroethylenepropylene (FEP) films to measure pressure changes in sealed chambers, as in distribution transformers. Voided film structures are very sensitive to pressure variations due to their low mechanical resistance in the thickness direction. Here voided capacitors were fabricated using the same thermal lamination process reported to produce piezoelectrets with open tubular channels. In order to measure pressure disturbance an electrical circuit was specifically designed for detecting variations in capacitance and results correlating these changes with pressure increase are presented.