  In this paper, we propose a solution to an AC state estimation problem in
electric power systems using a fully distributed Gauss-Newton method. The
proposed method is placed within the context of factor graphs and belief
propagation algorithms and closed-form expressions for belief propagation
messages exchanged along the factor graph are derived. The obtained algorithm
provides the same solution as the conventional weighted least-squares state
estimation. Using a simple example, we provide a step-by-step presentation of
the proposed algorithm. Finally, we discuss the convergence behaviour using the
IEEE 14 bus test case.
