Self-excited micro-hydro generator with voltage and frequency control

Smith, N.P.A., 1992. Self-excited micro-hydro generator with voltage and frequency control. PhD, Nottingham Trent University.

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Standard induction motors can be used as generators by simply connecting capacitors across the terminals of the machine. Induction machines are widely available, very robust and can be as little as one third of the cost of synchronous generators. However, hitherto, the controllers developed for stand-alone induction generators have been more costly and complicated than for synchronous generators. As a result, the complete induction generator systems were no cheaper or simpler than the well proven synchronous generator systems. The aim of this work has been to develop and demonstrate a new control approach which reduces the cost and complexity of induction generator systems sufficiently to make them preferable for micro-hydro schemes.

A fundamental investigation examines the acceptable voltage and frequency limits for small rural electrification schemes. This shows that in all cases the supply frequency can be allowed to increase significantly above its rated value. A turbine-induction generator model is developed and proven by comparison with experimental results. This is used to show that, with fixed excitation and voltage control by means of a variable ballast load, acceptable frequency regulation can be achieved for load power factor variations from 1 to 0.8 lagging. This approach eliminates the need for the costly and complicated variable leading VAR source used with conventional control systems. The resulting control system is no more expensive or involved than controllers for synchronous generators.

A variable mark-space ratio approach to ballast control has been developed, as this has advantages over the conventional methods. Care has been taken to design a robust, low- cost controller and this has been fully tested on hydro sites in England. Engineers from developing countries have been trained to locally manufacture the controller and, to date, fifteen locally manufactured units have been installed in Nepal, Sri Lanka and Indonesia.

Item Type: Thesis
Creators: Smith, N.P.A.
Date: 1992
ISBN: 9781369324037
Divisions: Schools > School of Science and Technology
Record created by: Linda Sullivan
Date Added: 10 Nov 2020 15:33
Last Modified: 04 Oct 2023 14:23

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