Simulador eletrônico de cargas com capacidade regenerativa e controle de tensão para testes em transformadores de potência

Abstract

The long duration tests of electrical transformers are important tools for users and manufacturers to determine precise information as, for example, equipment operational limits, lifespan, thermal behavior, etc. Although useful, these tests are usually conducted using passive elements such as in the burn-in test, consuming a great amount of energy and with limited flexibility to emulate different loading profiles (e.g., current and voltage levels, harmonics content, etc.).

In this context, to perform tests in power transformer emulating its real operation conditions can be a difficult task, since the standards procedures do not emulate several loading levels and the burn-in test consumes a high quantity of energy. Moreover, in distribution networks, the transformers are submitted to an increasing level of voltage and current distortions, besides voltage and frequency fluctuations. Thus, it is important to test them under these conditions, emulating more realistic operational behaviors. The use of electronic load simulator (ELS) is an alternative to conduct such tests, and it also can have regenerative proprieties, which is consuming just the system's intrinsic losses, besides emulating different types of loads.

This thesis presents a power electronics based ELS to perform tests in power transformers with low energy consumption that is capable of imposing, in controlled manners several levels of voltage and current, including harmonics components. The proposed system is designed and evaluated using classical control structures, and it is validated by computational tools and experimental results of a 50 kVA prototype. Furthermore, it is presented the studies a design methodology for the SEC's output filters and a LQR (linear quadratic regulator) resonant control structure. These studies are conducted in order to explore the proposed ELS particularities and, therefore, expand the range of transformer that can be tested. Lastly, the results of computational simulations are used to evaluate these studies, demonstrating the advantages of proposed modifications, and defining the test operational limit in accordance with the transformers characteristics.