  Modern societies crucially depend on the robust supply with electric energy.
Blackouts of power grids can thus have far reaching consequences. During a
blackout, often the failure of a single infrastructure, such as a critical
transmission line, results in several subsequent failures that spread across
large parts of the network. Preventing such large-scale outages is thus key for
assuring a reliable power supply. Here we present a non-local curing strategy
for oscillatory power grid networks based on the global collective
redistribution of loads. We first identify critical links and compute residual
capacities on alternative paths on the remaining network from the original
flows. For each critical link, we upgrade lines that constitute bottlenecks on
such paths. We demonstrate the viability of this strategy for random ensembles
of network topologies as well as topologies derived from real transmission
grids and compare the nonlocal strategy against local back-ups of critical
links. These strategies are independent of the detailed grid dynamics and
combined may serve as an effective guideline to reduce outages in power grid
networks by intentionally strengthen optimally selected links.
