Electrical Design of Variable Speed Hydroelectric Units

Historically, hydroelectric units have been of a conventional design whereby the output terminals of the generator connect via switchgear to the grid. With few exceptions (e.g., Powerformer™ high-voltage generators) the connections to the grid are usually made with a generator step-up (GSU) transformer that increases the generator terminal voltage to a level commensurate with the voltage of the transmission/distribution grid. Both asynchronous and synchronous generators have been used in this type of configuration.

A Task Force was formed to investigate if present electrical standards adequately address electrical design aspects unique to variable speed hydroelectric (VSH) units1. The Task Force researched available resources from industry, government and professional organizations to identify the standards that are directly applicable to VSH design and what, if any, deficiencies exist.