Modelling and Dynamic Performance of Hydropower in Frequency Regulation : Modelling of Double Regulated Hydropower Turbines

Sammanfattning: The frequency of the Nordic power system has been increasingly deviating outside the normal frequency band (50 ± 0.1 Hz) in the past two decades. In an effort to counteract this, the Nordic Transmission System Operators (TSOs) have proposed new and stricter requirements on the units participating in Frequency Containment Reserve (FCR) market. The implication of these new requirements is that all units participating in the FCR markets must be re-evaluated and early predictions state that double regulated (DR) hydropower turbines, such as Kaplan and Bulb types, will have problems meeting these new requirements. To limit the amount of work required to re-evaluate all DR turbines, which might ultimately show that the unit will not pass the requirements, it is highly beneficial for power producing companies to be able to simulate the turbine response accurately enough, without full-scale physical testing, to filter out the possible cases from the impossible ones. This thesis is aimed at finding a hydropower turbine model that could accurately predict the FCR prequalification outcome for a DR hydropower turbine in Simulink from only pre-existing testing and design data. Three hydropower turbine models, one single regulated (SR) and two DR, were tested and validated for FCR Normal operation (FCR-N). The validation was performed by comparing the model results to field test data attained from a full-scale FCR-N test performed on one of Fortum’s DR hydropower units. Furthermore, two of these models were simulated and tested with regard to the FCR Disturbance (FCR-D) requirements but not validated as no such data was available. The results showed that simulating DR turbines with SR models can give inaccurate results as the SR model could not capture the more complex dynamics of the DR turbine accurately enough. The SR model underestimated the active power response drastically while at the same time overestimating the dynamic stability. The DR turbine models managed to capture the dynamics better with the most prominent model, DR Model 2, giving less than 3 % overestimation of the FCR-N capacity and a correctly predicting that the unit would fail the dynamic stability for FCR-N. The thesis results further showed that when modelling DR turbines, the calculation of the net head is vital for accurate model response. Finally, both the SR and DR model agreed that the unit would likely not pass the FCR-D requirements and therefore confirm the early predictions that DR hydropower turbines, such as the one modelled in this thesis, may have problems passing the new FCR prequalification requirements. Ultimately this might impact electrical price or frequency quality negatively.