Método de detecção de falhas em transformadores de distribuição de poste com proteção operada

Abstract

According to CEMIG estimates, maintenance crew perform around 100.000 switching operations in fuse equipped air switches, installed in distribution transformers, every year. Since approximately 5600 transformers are replaced annually due to internal faults, 5.6% of the switching operations can be considered risk operations, as thetransformers to be energized are faulty. CEMIG adopts methodologies for field test of the transformers to minimize the risk of accidents, but these are excessively long since the lower voltage terminals needed to be disconnected. This work presents an efficient method for failure detection in three-phase and single-phase pole mounted distribution transformers whose protection has operated, without the disconnection of the low voltage terminals. The failure detection is done using two tests: one using low voltage and low frequency (LVLF) and the other using highvoltage and high frequency (HVHF). The former provides information about the pseudotransformer ratio (PTR) and the later comparing impulse voltages at different voltage levels. The combination of these two tests permits the failure detection in transformers efficiently, with reduced time, and without the disconnection of the low voltage terminals. Such time reduction in the transformer test diminishes the total recovery time, improving the power delivery quality