  Local changes in the topology of electricity grids can cause overloads far
away from the disturbance, making the prediction of the robustness against
changes in the topology - for example caused by power outages or grid
extensions - a challenging task. The impact of single-line additions on the
long-range response of DC electricity grids has recently been studied. By
solving the real part of the static AC load flow equations, we conduct a
similar investigation for AC grids. In a regular 2D grid graph with cyclic
boundary conditions, we find a power law decay for the change of power flow as
a function of distance to the disturbance over a wide range of distances. The
power exponent increases and saturates for large system sizes. By applying the
same analysis to the German transmission grid topology, we show that also in
real-world topologies a long-ranged response can be found.
