Improvements to a key contributor of frequency control : the co-ordination of guide vane operation in a pumped storage plant

Master Thesis


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University of Cape Town

The South African grid has been experiencing small reserve margins from 2008 and this will continue until the new power stations are integrated onto the grid. This is a time where the frequency control performance has become an important indicator to see how the power plants are able to deal with the restoration of frequency specifically during peak times. A study was done to identify the systems/aspects which at the time contribute a considerable amount to frequency control or could affect frequency in the medium to long term. From this, the co-ordination of the guide vanes at pumped storage plants was selected. Pumped storage units exhibit a non-minimum phase characteristic which can negatively affect the frequency response on the grid. Attempts were made to improve this system’s contribution to frequency control. To achieve this, the main waterway, including surge tank and guide vanes of a pumped storage station were modelled in a thermal-hydraulic simulation environment. With the model it was possible to realise the reverse power phenomenon inherent in pumped storage plants. The model was validated with similar studies in the literature and pumped storage plant data. A selection of scenarios with various guide vane operation techniques were proposed to improve the performance of two connected units during load changes. Some of the techniques produced improvement in the reverse power characteristic while others produced deterioration in the performance due to coupling of the unit using a common penstock but enjoyed an improvement in the plant net output. The study showed that it is possible to reproduce the non-minimum phase characteristic of a pumped storage plant using thermal-hydraulic models, and that various control schemes can be tested using the model. This paves the way for more elaborate control scheme evaluations, including those that look at coordination of all the pumped storage plants on a network.

Includes bibliographical references.