A centrality measure has been proposed considering the directionality of power flow of future smart grid. Applicability of the proposed method has been evaluated in several standard IEEE test systems. Various comparisons are shown between impacts of removal of critical nodes found from two different models: nondirectional and bidirectional. Larger impact of removing critical nodes found from bidirectional flow model shows the utility of the proposed method. Measures of impacts considered are changes in path length, loss of connectivity and load lost during cascade.