Methods, systems, and apparatus, including medium-encoded computer program products, for selecting, from a unified electrical power grid model, a first proper subset of elements of the model. A first electrical grid simulation model is selected. A second, differing proper subset of elements of the model are selected. A second electrical grid simulation model that differs from the first electrical grid simulation model is selected. A set of boundary conditions common to the first electrical grid simulation model and the second electrical grid simulation model are determined. Operation of the electrical power grid is simulated, and can include (i) simulating, using the first electrical grid simulation model, the first proper subset of elements of the unified model, and the set of boundary conditions; and (ii) simulating, using the second electrical grid simulation model and the second proper subset of elements of the unified model, and the set of boundary conditions.