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The benefits of adjustable speed: adjustable speed pump-turbine technology using solid-state power electronics can bring significant advantages to pumped storage installations. However, with the notable exception of Goldisthal (pictured above), there has, as yet, been very little experience with the technology outside Japan.

Article Excerpt
The first European pumped storage plant with adjustable speed technology, Goldisthal, has only recently started up (see Modern Power Systems, March 2003). But the technology has been used in Japan since 1990. The table below summarises commercial projects to date. The two Yagasawa projects were conversions of single speed machines to adjustable speed.

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Benefits

The benefits of using an adjustable speed machine in a pumped storage hydro plant include:

* Increased overall annual efficiency of 3% or more.

* Part load pumping.

* Frequency regulation in pump mode.

* Reduced vibration and mechanical wear.

* Increased pump-turbine life.

* Fish friendly turbine operation.

* Power system stabilisation.

Increased overall efficiency results from the fact that the pump-turbine can be operated at peak efficiency in both pumping and generation modes. With a conventional single speed machine, the pump-turbine can only achieve its peak efficiency in one of the two modes--not both.

Part load pumping means increased operating flexibility and possible lower costs for pumping power. With adjustable speed, it is possible to operate the pumps in the range of 60% to 100% of rated capacity. This means that a unit does not...