Detection of acoustic emissions from partial discharges in distribution transformers with piezoelectret transducers

Transformers are critical equipment in electrical energy systems and their failure may lead to loss of power supply. Major problems are normally avoided by preventive maintenance and implementation of fault detection systems on power transformers. Some of these systems are based on Partial Discharge (PD) detection methods, since PD is known to be one of the main causes of failures in transformers, such as those intended to power distribution. However, due to the large amount of such equipment installed on distribution lines, these monitoring methods may become very expensive. In order to increase the reliability of the grid, distribution transformers have been receiving more attention. In this context, this paper presents a low-cost transducer based on thermoformed piezoelectrets to detect PD acoustic emissions in distribution transformers. PD were produced using point-plane electrodes placed inside the tank of a distribution transformer filled with mineral oil. The PD acoustic signals were detected by a R15I sensor and a thermoformed piezoelectret transducer, previously validated in the acoustic PD detection in the air gap point-point electrode configuration. The PD acoustic signals were processed to obtain two metrics: root-mean value voltage and frequency spectrum. Based on these metrics it was possible to establish a direct correlation between applied voltage and PD activity.