Power sector vulnerability has been a key issue in society for over a decade. A component failure may trigger cascades of failures across the grid and lead to a large blackout. Complex Network approaches have shown a direction to study some of the problems faced by power grids and it is a continuing challenge thus far. Power grids have been studied for their structural vulnerabilities using purely topological approaches. A purely topological approach assumes that flow of power is dictated by shortest paths. However, this fails to capture the real flow characteristics of power grids. We have proposed a flow redistribution mechanism that closely mimics the flow in power grids using the \ac{PTDF}. With this mechanism we enhance the already existing cascading failure models to study the vulnerability of power grids. We apply the model to the European high-voltage grid to carry out a comparative study for a number of centrality measures. `Centrality' gives an indication of the criticality of network components. Our model offers a way to find those centrality measures that give the best indication of node vulnerability in the context of power grids, by considering not only the network topology but also the power flowing through the network. In addition, we use the model to determine the spare capacity that is needed to make the grid robust to targeted attacks.