In short-term hydrothermal coordination (STHC), the transmission network is typically modelled through a DC power flow. However, this modelling can lead to inoperable solutions when verifying with AC power flow. A methodology that includes an AC power flow model to overcome the problem applied to STHC is presented. The approach takes into account issues such as congestion management and control of quality of service, which are often present in large and weakly meshed networks - the typical pattern of Latin American electrical power systems. Generalised Benders- decomposition together with more traditional and well-known optimisation techniques, is used for this problem. The master problem stage defines the generation levels by considering the inter-temporal constraints, whereas the sub-problem stage determines both the active and reactive economical dispatches for each step of the load curve. It meets the electrical constraints (nodal balance, transmission limits and voltage levels) through a modified AC optimal power flow. The methodology was proved over a nine-busbar hydrothermal system and the solution found was validated with a quasi-exhaustive enumeration procedure to prove the optimality of the solution. Also proved over large system was the feasibility to realistic systems.