TITLE:
Small and Mid-Size Pump-Turbines with Variable Speed
AUTHORS:
Jürgen Krenn, Helmut Keck, Manfred Sallaberger
KEYWORDS:
Grid Stability; Pump Storage; Variable Speed; Full Size Converter; Wind Energy
JOURNAL NAME:
Energy and Power Engineering,
Vol.5 No.2A,
April
30,
2013
ABSTRACT: The stability of the grid is jeopardized with the large percentage
of non-dispatchable renewables like wind power and also with increasing solar
power. This creates various problems because these forms of energy are very
volatile and difficult to predict. In most countries the in-feed of these
sources must not be curtailed. In addition most of the renewables do not
provide short circuit capacity and inertia in the same way as classical units
and so further worsen the stability of the grid. The growing exploitation of
wind and solar might be limited due to grid stability problems. In order to
compensate those problems a large amount of reserve capacity is needed and
therefore new technologies for electricity storage are required. Hydraulic
pumped storage—the classical storage technology—has some disadvantages. These
plants are in mountain regions often far away from wind farms. The distance to
the wind farms mean additional loading for the already stressed grid and
additional transmission losses. To compensate the very volatile wind energy,
the pump input power should be varied continuously. This is so far only
possible with variable speed units. Up to now double-fed asynchronous
motor-generators are used which are rather expensive. In order to provide
a solution for the described situation, ANDRITZ HYDRO has developed a new
innovative concept of decentralized pump storage plants. Small standardized
pump turbines are combined with a synchronous motor-generator and a full size
converter which allows speed variation in pump and turbine mode over a wide
range. These plants can be built locally close to wind farms and other sources
to be balanced, allowing the increase of renewable energy without increasing
the transmission line capacity. For the future smart grids this will be a
key storage technology. This concept is reliable, innovative and more economic
than other storage technologies.