In the area of hydraulic power generation, there is a great deal of interest in two interdependent domains: operation and maintenance. This interdependence is usually simplified, or even ignored, to tackle the issue raised by the difference in planning horizons scales in each of these domains, causing conservative planning for the maintenance and missed opportunities in operation. This paper presents a new model for the simulation of the operation of a complex system that is a hydraulic power-generating grid, over an arbitrary long horizon, with a small step, in a reasonable time through a sequential resolution of the hourly operational plan of the system. The model is used to assess the influence of operation decisions (in this case, the start-up order of generating units) on the reliability of components through uptime, start-ups number and mode of operation over a medium horizon. A preliminary case study is presented using a standard operation strategy and its counterpart to validate the approach.