  The optimal transmission switching problem (OTSP) is an established problem
of changing a power grid's topology to obtain an improved operation by
controlling the switching status of transmission lines. This problem was proven
to be NP-hard. Proposed solution techniques based on mixed-integer formulations
can guarantee globally optimal solutions but are potentially intractable in
realistic power grids. Heuristics methods cannot guarantee global optimality
but can provide tractable solution approaches.
  This paper proposes solving the OTSP using exact formulations alongside
parallel heuristics that generate good candidate solutions to speed up
conventional branch-and-bound algorithms. The innovative aspect of this work is
a new asynchronous parallel algorithmic architecture. A solver instance solving
the full OTSP formulation is run in parallel to another process that
asynchronously generates solutions to be injected into the full OTSP solution
procedure during run time.
  Our method is tested on 14 instances of the pglib-opf library: The largest
problem consisting of 13659 buses and 20467 branches. Our results show a good
performance for large problem instances, with consistent improvements over
off-the-shelf solver performance. We find that the method scales well with an
increase in parallel processors.
