2 Hydraulic Machinery
2.1 Selection of Turbine
2.1.1
The selection of turbine type shall be made by putting forward alternative types of turbine in accordance with the range of operating head and operating characteristics of hydropower plant.And technical and economic comparisons,such as technical performance,economic indicators,operational reliability as well as experience in design and manufacture,etc,shall be made to justify the rationality of design.
For a run-of-river hydropower plant with maximum head of 20m and below,priority should be given to tubular turbine.
2.1.2
The selection of unit capacity and the number of units shall be determined by technical and economic comparisons according to the unit capacity alternatives worked out based on the following factors,and the number of units should not be less than 2.
1 The requirements of power grid for the power output in the flood season and the non-flood season,the unit operating mode and overhaul,as well as the proportion of unit capacity to the working capacity of power grid.
2 The regulation property,characteristics of head and discharge,and operating mode of reservoir.
3 The requirements of the ecological flow or the minimum navigation flow in downstream river channel.
4 The overall layout conditions.
5 The external transportation conditions.
6 Sediment characteristics of rivers and that through tur bine.
7 The units manufacturing possibility.
8 The recent and long-term scale of the hydropower plant.
9 The ice conditions of reservoir and river.
10 Other special technical requirements.
2.1.3
For the Francis turbines with a large ratio of maximum head to rated head,the necessity and rationality of turbine operating in over rated power may be studied according to the requirements for the stable operation range in high head range.
2.1.4
The rated head of a turbine shall be selected through technical and economic comparisons and based on the consideration of comprehensive factors such as the regulating property and operating mode of the reservoir,roles and functions of the hydropower plant in the power grid,operating head and output range of the plant,operation stability of the turbine,generating capacity and the head loss of water conveyance system.In addition,the following requirements shall be complied with:
1 For medium or high head turbine,the rated head should be selected within the range of 0.95-1 times of the weighted average head.
2 For a run-of-river hydropower plant,the rated head of turbine shall ensure the full output of all units.
3 For the hydropower plants located on sediment-laden rivers and with their reservoirs operating in the mode of "storing clear water and releasing muddy flow",the rated head of turbine should be selected between the weighted average head and the lowest operating head during reservoir impoundment period.
4 The rationality and economy shall be justified when the rated head approximates to the minimum head.
2.1.5
The selection of turbine specific speed shall meet the fol lowing requirements:
1 The conditions including the operating head,water quality,design levels,manufacturing capability,etc.shall be considered comprehensively.
2 For turbines which operate on sediment-laden rivers or with large head variation or at high altitude area,lower special speed shall be adopted.
2.1.6
The rated speed of turbine shall be selected from the generator's synchronous speed series on the basis of the parameters such as the operating head,unit capacity and runner diameter or the specific speed.When two or more synchronous speeds are available,the speed shall be determined through technical and economic comparisons.
2.1.7
The selection of turbine suction height shall meet the following requirements:
1 The suction height of reaction turbine shall be calculated on the basis of different operating conditions under various characteristic heads and the plant cavitation factor σp respectively.In addition,the influence of local absolute elevation shall be considered.
2 The plant cavitation factor should be selected in accordance with the incipient cavitation factor σi.When no incipient cavitation factor is available,the plant cavitation factor may be determined by multiplying the critical cavitation factors σc with the ratio coefficient kσ.
2.1.8
The selection of turbine setting elevation shall meet the following requirements:
1 The setting elevation of turbine shall be determined through technical and economic comparisons on the basis of necessary suction height of turbine under different operating condi tions and corresponding tailwater levels.
2 The design tailwater level for determining the turbine setting elevation shall be defined in accordance with the factors such as the operating mode of the reservoir,the output range of the plant,the characteristic of tailwater level to flow discharge,the requirements for power generation in early stage and the operating levels of downstream cascade hydropower plants,etc.The selected turbine setting elevation shall meet the requirements that the minimum submergence depth at the upper edge of the draft tube (or tailrace tunnel) outlet shall not be less than 0.5m within the allowable operating range of turbine.
3 The design curve of the draft tube (or tailrace tunnel) outlet shall be adopted when selecting the characteristic curve of tailwater level to flow discharge for determining the turbine setting elevation.
4 The setting elevation of Pelton turbine shall be determined in accordance with the maximum operating tailwater level of all units.The aeration height of tailrace should be sufficient under all generating conditions.
5 The setting elevation of tubular turbine shall be determined with consideration of the influence of the elevation difference in circular section.
6 The selected setting elevation of turbine should be given appropriate safety margin and shall meet the regulation guarantee requirement.
2.1.9
The maximum runaway speed of Francis turbine or fixed-blade turbine shall be determined by the maximum unit runaway speed under the maximum net head.The maximum runaway speed of Kaplan turbine shall be calculated according to on-cam condition.Off-cam condition may be adopted in the cal culation if specially required.The maximum runaway speed of Pelton turbine shall be determined by the maximum net head.
2.1.10
For new developed turbine runner,the model test data shall be supplied by manufacturer,and model acceptance test shall be performed if necessary.The new technology,technique and material,if applied,shall be justified by test and technical appraisal.
2.1.11
The rationality,reliability and applicability of the structural design of turbines shall be studied in the selection of turbine.Anti-cavitation measures shall be taken for the flow passage prone to cavitation pitting.For turbines operating in water containing a significant amount of solid,measures shall be taken to prevent sand erosion.The structures shall be designed to facilitate the maintenance and replacement of the wearing parts.
2.1.12
For the selected turbine,the manufacturer shall provide the technical information such as guarantee value for output,efficiency and discharge,cavitation or abrasion loss,runaway characteristics,operational stability and noise,regulation guarantee,reliability,hill chart of model and characteristic curves of prototype turbine,etc.
2.1.13
The types and dimensions of spiral case and draft tube proposed by the manufacturer should be selected,and the satisfactory hydraulic performance and operational reliability shall be guaranteed.
Anti-leakage measures shall be taken for concrete spiral case.
If there are special requirements due to powerhouse layout or other factors,the modification of shape and dimensions of the draft tube shall be determined by consulting with the manufac turer.Turbine model test should be performed once more if necessary.
2.1.14
The conical part of draft tube shall be lined with metal liner.For the elbow bend of the elbow draft tube,metal liner should be used when the mean flow velocity in the elbow is 6m/s and above.