Modelagem de transformador de distribuição monofásico para estudos de transmissão de dados de PLC em banda estreita de frequência

Abstract

The use of the power grid for data transmission, technology known as Power Line Communication (PLC), is one of the communication solutions available for smart grid applications. In general, the PLC system must be capable of ensuring data transmission along medium voltage distribution lines and between medium-voltage (MV) and low-voltage (LV) distribution networks. However, the interface between these networks is established by distribution transformers. As the terminal relations introduced by this equipment present frequency-dependent characteristics, the transformer eventually modifies the transmitted signals. This work proposes models to characterize the role of a single-phase distribution transformer of 10 kVA, 7967/240-120 V, in the context of PLC applications. This transformer, which is widely used in rural distribution networks in Brazil, was represented in a wide range of frequencies using the black-box modeling technique. The proposed models are valid for typical frequency ranges of narrowband PLC applications, from 3 to 500 kHz, and in the CENELEC band (3 to 148.5 kHz). The models were obtained in both phase and modal domains from the measurement of admittances and voltage transfer ratios. At first, the measured frequency responses were approximated by rational functions using the vector fitting technique. Then, compact equivalent circuits were synthesized, whose parameterization is provided in this work. The validation of the models is performed through studies comparing measured data and simulation results in the frequency and time domains for different load conditions, considering the transmission of signals in the MV-LV and LV-MV directions. The results indicate that the models reproduce the transformer behavior satisfactorily for all tested terminal conditions and both domains. Also, frequency bands have been identified in which the signal attenuation is reduced, which may support the transmission of PLC signals through distribution transformers.