Contribuição a automação do ensaio de elevação de temperatura de transformadores de distribuição imersos em líquido isolante

Abstract

In the year of 2001, the Brazilian Government published the Law of Energy Efficiency, which established regulations for the efficiency in electrical equipment. On that occasion, the Brazilian Government also created the Program of Labeling, which originated the National Label of Energy Conservation (ENCE, in Portuguese). In that context, the National Institute of Metrology, Quality and Technology (INMETRO, in Portuguese), released the ordinance number 510, establishing the specifications for the program of compliance evaluation for distribution transformers immersed in liquid insulation. Among the mandatory tests that should be performed, there is the temperature rise test (I.e. Heat Run), in which is made the measurement in the top of the oil of the transformer, while the equipment is submitted to its load losses. The metrologist can end the test when the variation of temperature is lower than 1° C during 3 hours, what usually demands about 10 to 12 hours of testing. Therefore, in search to automate the temperature rise test, in this Final Paper is proposed the development of an instrumentation electronic circuit to monitor the electrical and thermal signals originated by the test, including a monitoring system and a web page. The research contains a literature review about the topics covered in the development of that project. Between said topics, there are the electronic instrumentation, communication protocols, web development and the measurement tools inside the Medium Voltage Laboratory of the Smart Grid Institute, which is located in the Federal University of Santa Maria. The project of the printed circuit board (PCB) has two main phases. The first one is about the designing of the instrumentation electronic circuit and its assembly. After test and validation of the designed circuit, the second phase started, that consisted in the software development, formed by the monitoring system and web page. The monitoring system is responsible for receive the data of the PCB and, after the analysis of said data, it does the automatic control of the power supply through the Modbus communication protocol. At last, the metrologist, or the assistant, can, by request, select and send the relevant data of the monitoring of the temperature rise test to the web page. That way, it is possible to implement the automatic control of the power supply, as well the remote supervision of the test by the metrologist, fact that contributes to the automation of the laboratory.