Application of single phase switching on Entergy System: three phase unbalance studies

The Webre-Richard 500 kV line is a major transmission facility in the Entergy System. The loss of this line when carrying large power blocks can lead to overloads on the underlying system and voltage collapse in the Lake Charles area, especially under high load and low generation conditions. Also, a large power angle difference between the two areas of the system makes it difficult to close the line without adjusting loads and generation. In order to address these concerns, several alternative solutions were considered and a decision was made to implement the single phase switching (SPS) scheme on the Webre-Richard line to enhance the reliability of transmission system. One of the several factors considered in designing SPS is the effect of unbalance on the performance of transmission and nearby generating plants. This paper discusses an approach for analyzing system unbalances using three phase load flow feature of EPRI´s Electromagnetic Transients Program (EMTP) and utilization of the results in the design of the Webre-Richard SPS scheme.