Electrical Design of Variable Speed Hydroelectric Units

Historically, hydroelectric units have been a conventional design whereby the rotational speed of the generators is fixed by the frequency of the grid to which they are connected. The development of high-energy power semiconductors has made it practical to use frequency converters as a method to adjust the rotational speed of a variable speed hydroelectric (VSH) unit independent of the electrical frequency of the grid. Two types of VSH units are described, including a discussion of the benefits of each. Various resources available from industry, government and professional organizations were researched to identify the standards that are directly applicable to VSH design and what, if any, deficiencies exist.