Abstract
The objective of this paper is to investigate the cause of several unexpected high amplitude oscillations that occurred in the surge tank water level of a real hydropower plant during secondary load-frequency control (LFC) maneuvers, after the replacement of the turbine runner, and to propose solutions that allow the power plant to continue providing secondary LFC in a safe and reliable manner. For this purpose, a simulation model has been developed and calibrated from data gathered during several on-site tests. Two different solutions are proposed in order to cope with the observed problem: using a state-dependent load change rate limiter or modifying the hydro turbine governor gains; the turbine governor remains the same as before the runner replacement. The proposed solutions are tested against a set of realistic secondary LFC signals by means of simulations and compared to each other as a function of the probability that the surge tank water level descends below a minimum safe level and the quality of the secondary LFC response. The results presented in the paper demonstrate the validity of the methodology proposed to determine the state-dependent ramp limit, as well as its effectiveness to prevent the surge tank drawdown and to provide clear insight into the trade-off between response quality and power plant safety.
Highlights
Energy (103GWh)Regulation energy (GWh)During the last few decades, renewable energies experienced a continuous growth
A simulation model has been used to investigate the cause of several unexpected high amplitude oscillations that occurred in the surge tank water level (STWL) of a real hydropower plant during secondary load-frequency control (LFC)
The cause of the high amplitude oscillations turned out to be a sort of resonance phenomenon, which takes place when the power plant operates under the control of an automatic generation control system (AGC) system, in response to some sequences of power set-point signals that meet certain conditions
Summary
During the last few decades, renewable energies experienced a continuous growth. In Europe, this growth was promoted by several European directives, as well as by the corresponding country regulations. A simulation model is developed to investigate the cause of several unexpected high amplitude oscillations that occurred in the surge tank water level (STWL) of a real hydropower plant during secondary LFC maneuvers, as well as to propose solutions that allow the plant to continue providing secondary LFC in a safe and reliable manner. The dynamics of the secondary LFC loop may couple with that of other elements of the power plant with similar time constants, such as the surge tank For these reasons, it seems obvious that the secondary LFC loop response should not be studied on the basis of a small disturbance analysis, but with the help of non-linear simulation models [19].
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