Development of Ultra High Head Large Capacity Pump-Turbines for Pumped Storage Power Plants with More Than 700m Head Shigenori Watanabe, Tokyo Electric Power Company, Kiyoshi Matsumoto, Toshiba Corporation, Kazuo Niikura, Hitachi, Ltd. Yoshihiro Iwasaki,  Mitsubishi Heavy Industries, Ltd. 1. General
The head and the unit capacity of pump turbines tend to be higher and larger, respectively aiming to expand the possible site and to reduce the construction cost of pumped storage power plants.
The pump turbines currently in use have a head of up to 500m, 350MW and up to 700m, 200MW class (Fig. 1).
Tokyo Electric Power Co., Inc. (TEPCO) planned the Kazunogawa pumped storage power station of 1.6GW utilizing the head of over 700m. However the possible plan, at that point, was to additionally construct an intermediate power plant, and the accompanied reservoir in order to share a half head of 700m with another power plant of the lower reservoir. This plan seemed technically possible but economically not feasible.
There was an urgent need to develop an Ultra high head, large-capacity (779m-500rpm-400MW) pump turbine. TEPCO collaborated with Toshiba, Hitachi, and MHI to develop the essential technologies of design, manufacturing, and installation for ensuring the quality and reliability of the pump turbines (Fig. 2). 
In Kazunogawa power station, the first unit was put into commercial operation in December 1999, and the second unit in June 2000. The smooth and stable operation of the units proved the high reliability of the developed units. The technologies here developed have contributed largely to the future plan and the present construction of pumped storage power plants having further higher heads.
The third and the fourth units of Kazunogawa power station are adjustable speed machines. The construction of these units will proceed according to the power demand in the future.

2. Detail of the Technologies
(1) Development of high-performance pump turbine runner
In order to ensure the strength reliability of the runner, the special care should be paid not only for the static stress due to the high static pressure and the centrifugal force of the high speed runner, but also the vibration stress due to periodic pressure pulsation which is caused when the runner vanes pass through the wakes of the guide vanes outflows.

When the frequency of the pressure pulsation is close to the natural frequency of the runner in water, a resonance can excessively enlarge the stress amplitude of the runner and lower the strength reliability. Following technologies have been developed. 
1) Dynamic analysis method for hydraulic pressure pulsation and runner resonance in water.
2) Adjusting technique of the natural frequency of the runner in water for avoiding runner resonance.
3) Casting and defects inspection technologies for producing non-defective pump turbine runners.
4) Non-destructive inspection method for detecting minute defects.

(2) Development of pump turbine components that meet the ultra high head requirements
With a very increased head, the stationary components of the pump turbine are also subjected to the large hydraulic pressure. Under such a condition even a minor problem can be a trigger of some serious accidents. The reliability of the components is ensured as follows;
1) Fluid design technology utilizing quasi-three dimensional analysis and steady/unsteady turbulent flow analysis (LES/DNS) to optimize the flow and reduce the hydraulic pressure pulsation.
2) Structural design technologies such as strength analysis, vibration analysis, and assembly simulation using three-dimensional CAD/CAE.
3) The shaft-sealing device to meet the high pressure and high-speed conditions.
4) Low air leak-draft tubes in condenser operation to meets the deep submergence.
5) gOh rubber strings sealing the water pressure of 12MPa between the speed ring and upper and lower covers. 
6) High accuracy site installation technology applying in site machining.

3. Summary
These developed technologies have been applied also for the pump turbines (713m-500rpm-450MW) of Kannagawa pumped storage power station, which is now under construction. TEPCO is currently developing;
- The pump turbine with splitter blades, which have excellent hydraulic performance, low hydraulic pressure pulsation, and a large operating range of the output.
- The advanced governor applying modern control theory.
- Optimizing the adjustable speed pumped storage power generating system.
We will be pleased to transfer these technologies of the ultra  high head pump turbines to the world.

Fig.1 Unit Capacity and Pumping Head of Pump Turbines 

Fig.2 Pump Turbine of Kazunogawa Power Station

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