Conclusions
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1.
To reduce installation costs and construction times for diversion and dam hydroelectric stations, it is frequently possible and advisable to dispense with surge chambers.
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2.
A criterion for the measures adopted in order to exclude surge chambers from a hydroelectric scheme may be the penstock constant of inertia T l . As a guide: for T l =4–6 sec, the closure time Ts of the guide vanes must be increased for the normal power plant installation: for T l =4–6 sec, the closure time Ts of the guide vanes must be increased for the normal power plant installation; for T l =6–10 sec, on increasing Ts, changes are necessary in the design of the generator, ensuring reliability on attaining speeds of rotation approaching runaway during load shedding. Use of idle discharges enables a closure time Ts to be adopted, yielding an increase in rotational speed well below runaway; for T l >10–12 sec, it is necessary to install idle discharges.
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3.
The use of idle discharges not only enables surge chambers to be dispensed with for high values of T l , but also provides a reduction in water hammer and consequently the design pressure in the penstocks, at the same time reducing metal consumption for manufacture.
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4.
Complete calculations of the transient have to be carried out for each particular installation in the design stage, taking into account the characteristics of the turbines, regulators, and idle discharges. Only on the basis of a thorough and comprehensive analysis of the data and of the performance of the hydroelectric station on the system can the appropriate solution be adopted.
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5.
Overall investigations have to be carried out for hydroelectric stations with long penstocks and with idle discharges, in order to study the features of the transients, flow instability, resonance phenornena, and vibrations in the unit and installations, particularly for heads of 150 to 300 m. Questions affecting the improvement of design discharge structures must also be resolved.
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Literature Cited
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N. A. Arshenerskii, G. I. Krivchenko, V. V. Beshentsev, and V. S. Konviz, “Varying the regulationconditions of hydraulic units in order to reduce the cost of hydroelectric stations,” Gidrotekhnicheskoe Strotel’stvo, No. 8 (1966).
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Additional information
Editorial Note. The paper indicates the possibilities of lowering the cost of hydroelectric station construction with long penstocks by dispensing with surge chambers. It is proposed to increase the regulation time of the turbines or to establish idling discharges. Recognizing the value of the authors’ conclusions, the editorial board considers it necessary to add the following notes. A substantial increase in the regulation time of hydraulic units connected to the power system is acceptable in principle but requires specific justification in each case in order to provide the necessary run-up to power and dynamic stability of the sets on the system. In addition, the operating conditions must be assessed with a big increase in speed of rotation of the set each time it is disconnected from the network. The more the revs deviate from the normal, the more serious are the cavitation processes in the turbine, resulting in a high level of flow pulsations and vibrations. The problem must be studied from all angles on existing units. The use of idling discharges is not a new idea. It should be noted however that on all Soviet hydroelectric stations where they have been installed, they can be dispensed with according to modern ideas. This information is also given in the article. The example put forward by the authors, based on the Nurek hydroelectric station, is ambiguous. Another effective design solution has been found for this hydroelectric station without using idling discharges. Like all additional preventive measures, idling discharges lower the reliability of the unit, since failure may have catastrophic consequences. The authors of the article therefore favor storage, proposing duplication, which gives rise to further problems. Idling discharges also involve probable systematic loss of water through leaks, and their application therefore requires a direct comparison of capital investments. Nonetheless, since the savings in capital outlay may be substantial in individual cases, there is justification for working toward improving the procedures for determining the feasibility of idling discharges and seeking new, more reliable watertight design solutions, particularly for large-scale idling discharges. The article is also important since it poses these problems.
Translated from Gidrotekhnicheskoe Stroitel’stvo, No. 9, pp. 10–14, September, 1971.
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Arshenevskii, N.N., Trubitsyn, Y.N. Significance of dispensing with surge chambers to lower the cost of hydroelectric stations. Hydrotechnical Construction 5, 811–817 (1971). https://doi.org/10.1007/BF02403688
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DOI: https://doi.org/10.1007/BF02403688