  Networked power grid systems are susceptible to a phenomenon known as
Coherent Swing Instability (CSI), in which a subset of machines in the grid
lose synchrony with the rest of the network. We develop network level
evaluation metrics to (i) identify community substructures in the power grid
network, (ii) determine weak points in the network that are particularly
sensitive to CSI, and (iii) produce an engineering approach for the addition of
transmission lines to reduce the incidences of CSI in existing networks, or
design new power grid networks that are robust to CSI by their network design.
For simulations on a reduced model for the American Northeast power grid, where
a block of buses representing the New England region exhibit a strong
propensity for CSI, we show that modifying the network's connectivity structure
can markedly improve the grid's resilience to CSI. Our analysis provides a
versatile diagnostic tool for evaluating the efficacy of adding lines to a
power grid which is known to be prone to CSI. This is a particularly relevant
problem in large-scale power systems, where improving stability and robustness
to interruptions by increasing overall network connectivity is not feasible due
to financial and infrastructural constraints.
