Dynamic Behaviour of Reversible Pump-Turbines in Turbine Mode of Operation

摘要

A reversible pump turbine is a machine that can operate in three modes of operation i.e. in pumping mode, in turbine mode and in phase compensating mode (idle speed). Reversible pump turbines (RPTs) have an increasing importance for regulation purposes for obtaining power balance in electric power systems. Especially in grids dominated by thermal energy, reversible pump turbines improve the overall governor stability. Increased use of new renewables (wind, wave and tidal power plants) will utterly demand better regulation ability of the more traditional power suppliers, enhancing the need for reversible pump turbines. It is, however, a necessity that both machine and system is designed for maximum flexibility in changing modes of operation from pump to turbine and vice versa. A reversible pump turbine is known for having very steep speed-flow characteristics which might give stability problems. During the design process, focus on the system dynamics in such power plants is essential. Simulation of the dynamic behaviour of the system implies a good representation of the turbine by its characteristics. It is necessary to be able to represent the characteristics before any measurements of the actual machine are available. This paper presents an possible explanation of the reason for these steep characteristics. Based on this hypothesis, a representation of the turbine for system dynamic simulation purposes is suggested.