This paper is about start-up costs of hydro power units. In the introduction we address three questions about startups of hydro power units: " What causes the costs in the start-up? " How much does a start-up cost? " How do start-ups effect the short-term scheduling strategies of power producers in Sweden? In order to answer these questions, we have interviewed employees working with generation planing at the eight largest power producers in Sweden. We found five aspects causing start-up costs: " Loss of water during maintenance. " Wear and tear of the windings due to temperature changes during the start-up. " Wear and tear of mechanical equipment during the start-up. " Malfunctions in the control equipment during the start-up. " Loss of water during the start up. The aspects causing the largest costs are maintenance due to the wear and tear and the unavailability and personnel costs due to malfunctions in the control equipment. The cost of lost water is usually small. Our conclusions are the following: " Start ups cost. The cost will depend on the nominal power of the unit and the unit model. " The majority of the power producers consider start-ups in their planning. " There is a need for better knowledge about start-up cost. " There is a need for planning software which considers start-up costs of hydro units. © 1996 IEEE.
