Dynamic multi-period economic dispatch for large-scale power systems is considered. The formulation presented caters for loading and deloading rates, limits on generators outputs, spinning reserves requirements and group power import-export limits. It is also suitable for implementation within a constraint relaxation strategy. The solution algorithm is based on a Dantzig-Wolfe decomposition, which yields a capacitated transshipment subproblem along with a master problem solved by the Revised Simplex method.The computational efficiency of the algorithm renders it suitable for on-line dispatch.