Sensor optoeletrônico para verificação do estado de abertura em chaves seccionadoras de média tensão

Abstract

Given the necessity of the correct switching between disconnectors and circuit breakers, the knowledge of the disconnector state (i.e. open or closed) is a crucial information for the safe operation of the power grid. In the context of high voltage, the disconnectors are usually equipped with electromechanical sensors that verify the opening state of the disconnectors – while in the context of medium voltage, the disconnectors usually aren’t equipped with any sensor at all. The electromechanical sensors, over time, suffer from mechanical stress which leads to incorrect sensing. On the other hand, purely electronic sensors are not practical in these applications due to the strong electrical and magnetic fields present on the power lines, especially during the switchings. Thus, the use of an optoelectronic sensor in which an optical cord makes the sensing is advantageous, because the electronic circuit is physically isolated from the power lines through the high dielectric strength of the optical cord. Furthermore, as the sensor is mechanically fixed, it does not suffer from mechanical stress as an electromechanical sensor does. In this work, a medium voltage disconnector opening state sensing optoelectronic sensor is proposed. The sensor consists of an optic cord containing two fibers, an electronic circuit for generating and transducing light signals, a reflective screen and mechanical fixation elements. The proposed sensor went through experimental lab bench tests using a jig to simulate the disconnector angular aperture. The device managed to detect the reflective screen for different distances from the cord to the screen. However, false positives occurred for angles different (albeit close to) from 90° (which represents a perfectly closed disconnector). Thus, it was validated the use of the prototype for sensing the disconnector’s opening state, but further work is required to mitigate the false positive problem.