Sensor óptico para o monitoramento de chaves seccionadoras de média tensão isoladas a ar

Abstract

Continuous monitoring of equipment is essential to mitigate failures and defects, contributing to the reduction of financial losses for electric power utilities and consumers. In this context, this work presents the development of an optical sensor for monitoring medium voltage disconnect switches, equipment widely used in substations and power distribution networks. These switches allow, through operational maneuvers, the isolation of circuit breakers for maintenance without interrupting the power supply. The proposed system consists of a plastic optical fiber (PMMA), a biconvex lens, a reflective target, and an electronic circuit for signal conditioning and processing. The electronic circuit modulates the electrical signal into an optical signal using a laser diode operating at a wavelength of 650 nm and modulated at 1024 Hz. The optical signal emitted from the transmitting fiber (TX) is collimated by the biconvex lens and directed toward a target fixed to the blade of the disconnect switch. The beam is then retroreflected and partially returns to the lens, which focuses the beam onto a second plastic optical fiber receiver (RX), guiding it to the photodiode. The electronic circuit performs filtering and amplification of the received signal, which is then sent to a microcontroller responsible for analyzing the amplitude and spectral signature of the signal at the fundamental frequency of 1024 Hz, allowing the identification of the switch state. Prior to installation on the disconnect switch, the optical system was calibrated to optimize the signal response. In laboratory tests aimed at obtaining the sensor operating characteristic curve, 30 samples were collected at distances ranging from 2 cm to 50 cm. In the angular calibration tests, the system was able to detect, through variations in signal amplitude, a maximum angular opening of 3.11°, a condition associated with an increase in the contact resistance between the terminals of the disconnect switch. Additional tests were carried out under variations in temperature and humidity while maintaining the switch in the closed position, allowing the analysis of the signal amplitude and frequency behavior over time. Finally, in outdoor tests, the disconnect switch was exposed to rain and environmental conditions, with continuous monitoring of amplitude and frequency signals during the test period.