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HYdropower plants PERformance and flexiBle Operation towards Lean integration of new renewable Energies

To achieve a lean integration of new renewable energy sources, NRE, within the power network, the TSO, Transmission System Operator, needs to be able to perform a fast energy balance between generation and consumption. Therefore, it is necessary to ensure power plants have enough storage capacity as well as primary and secondary grid control capability, to enable this energy balancing process. Both gas fired and hydropower plants feature such a capacity of flexible generation for peak power and regulation ancillary services at a large scale. However, hydropower plants are offering the advantage of exploiting renewable primary source energy with almost no emission of greenhouse gas. Additionally, pumped storage power plants provide a system to store large amounts of electricity with a full cycle of pumping and generation, which can achieve unrivalled efficiency of at least 80%. To take up the challenge of enhancing the capability of hydropower plants to be operated over a larger operating range and with a faster time demand response, the HYPERBOLE Research Consortium partners have defined the 3 following science and technology objectives to be achieved.

First Objective

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It is to bring new knowledge of the root causes of the operating range limitations for both hydraulic turbines and pump-turbines to be operated over a wide operating range. When operated over a wide operating range corresponding to deep part load, below 30 % of rated power and up to overload operation, about 110 % of rated power, hydraulic turbines and pump-turbines experience these "off-design" conditions resulting in high levels of vibration and large pressure and power fluctuations. The mechanical structure experience high dynamic loads due to the strong and unsteady nature of the flow at these "off-design" conditions. Consequently, the life expectancy of the machine can be significantly reduced, eventually leading to the loss of structural integrity. Moreover, the unit operation may become so unstable that the unit will disconnect from the grid. This is the reason why the operating range is limited to between approximately 60 % and 100 % of rated power. Additionally, reversible pump-turbines are subject to a dramatic increase in the daily change rate between generating and pumping modes, which also may endanger the unit integrity. Therefore, experimental investigation of the reduced-scale physical models of both Francis turbine and pump-turbine will be carried out at the testing facilities of the project partners and the complex flow phenomena corresponding to these sources of excitation will be identified and extensively investigated by both experimental and advanced numerical tools including CFD and FEM.

 
Figure 1 CAD view of the reduced-scale physical model of MICA Francis Turbine, Unit 1, to be installed on EPFL PF3 test rig.

 

Second objective

It is to develop comprehensive multi component models of the hydropower plants dynamics based on and validated by reduced-scale physical model experiments and extensive field tests on both a pumped storage power plant, Aldeadávila II, Spain, and a conventional hydropower plant, MICA, Canada. The new knowledge achieved for the complex flow phenomena will involve the excitation sources of the dynamic loading of the hydraulic turbines when operated at deep part load, part load and overload. This will enable modelling of these sources to be performed. These models will be implemented for every operating condition case in SIMSEN, the advanced numerical simulation of systems dynamics tool develop by EPFL. SIMSEN is widely used by the industrial partners of the research consortium for simulating the hydropower plants dynamics, including hydraulic machinery and system, electrical machines and power electronics and the control systems. Advanced dynamic models of the electrical machine and power electronics system will be also developed. The resulting comprehensive multi component models of the hydropower plants dynamics will be validated by reduced-scale physical model experiments, see Figure 4, and extensive field tests for generating Unit 1 of the MICA power plant, located in British Columbia, Canada. Moreover, the assessment of the structural response and optimization of the mechanical design procedure for extending the component life time will be validated for the pump-turbine units of Aldeadávila II pumped storage plant, located on the Douro River in Salamanca Province, Spain (Figure 2).

 
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Figure 2 Photography of the spillway of Aldeadávila Dam, Salamanca, Spain. 

 

Third objective

It aims to demonstrate the benefits hydro power plants can provide to safely integrate new renewable energy sources, based on real selected case study. The enhancement of the operating range of Francis turbine and pump-turbines, as well as the capability of providing inertia emulation functionalities and primary and secondary control capabilities, together with new control strategies will contribute to increase the penetration of NRE in power networks. The control flexibility of new hydro units will be achieved through the exploitation of advanced energy conversion processes involving power electronic interfaces, either full scale converter or advanced excitation systems in Double Fed Induction Generators. As a result, the additional NRE connection capacity will be evaluated in a study case with respect to system stability using state of the art power network simulation models. The hydraulic models and related parameters to be considered in the power network simulation will be derived by comparison with fully detailed simulation models developed using simulation software SIMSEN. The detailed simulation will enable considering hydraulic waterways, hydraulic machines, electrical machines and the related control systems for hydropower plants. The comparison between detailed and reduced models will provide guidelines to model conventional hydro and pumped storage power plants including variable technologies with appropriate level of complexity for power network stability analysis. In addition to grid stability and security issues of power systems with a high share of NRE, the HYPERBOLE project aims also the development of an optimization algorithm for the identification of adequate strategies regarding the participation of a reversible hydropower plants in the secondary reserve market, in complement to the participation in the tertiary reserve market.