Abstract: We study cascading failures of the western United States power grid under three attack strategies,Initial load of an edge ij is defined as(k_ik_j)^θ with k_iand k_j the degrees of nodes connected with the edge,where θ is a tunable parameter.Three attack strategies are LL(attack on edges with the lowest load),SPC(attack on edges with the smallest proportion between total capacities of neighboring edges and capacity of the attacked edge)and HL(attack on edges with the highest load).It is observed that cascading failure scales are quite different under three attack strategies with different θ.Analyzing topology of the power grid in detail,we study otherness of cascading failures under three attack strategies.It shows that select ranges of attacked edges are not varied with θ under strategies of HL and LL.Attack effect of HL is enhanced with increasing θ,however,attack effect of LL is weaken with increasing θ. Select ranges of attacked edges of SPC varies with θ.At a small θ,attacked edges of SPC are belong to LL with a special topology,As θ increased,attacked edges of SPC tend to those edges with relatively high loads.Consequently,attacked effect of SPC is close to that of LL with a small θ and it is close to that of HL with a great θ.

Key words: western United States power grid, cascading failure, SPC