Compensation strategy of autotransformers and parallel lines performance, assisted by the UPFC

In this paper, reactive power compensation through the tertiary winding of an autotransformer, is proposed. Such an approach emerges as an alternative to support the significant voltage variation present over two parallel connected autotransformers, in the South Eastern Brazilian system. The above proposal will also help in controlling the line voltage variation due to the UPFC series converter action. A detailed steady-state analysis of the series voltage and the shunt reactive current when supporting line voltage, is realized. Such analysis is based upon the d-q coordinates. The UPFC effect over an uncompensated parallel line, is also studied. The waveform simulations performed to control each transformer terminal voltage, were obtained utilising the ATP/EMTP program. Results concerning the effectiveness of the autotransformer tertiary winding reactive power injection by the UPFC shunt converter, as well as the load flow control over the referred transformers, are also presented.