4.5　Selection of Installed Capacity and Type of Hydropower Unit

4.5.1　Installed capacity shall be selected on the basis of analysis of regulating performance of the reservoir，requirements for multipurpose utilization，system loading in the system design level year and its characteristics，scope of power supply and structure of power sources，and then finalized by calculating annual electricity production，power generation benefit and related costs of each installed capacity scheme，combining with a comprehensive comparison of electric power and energy output equilibrium.

4.5.2　The design level year may be determined with reference to the national economic planning of the system，scale of the hydropower station and its weight in the system.For the key hydropower station in the system，a period of 5-10 years after the first unit is put into operation may be adopted as the design level year of the hydropower station.

4.5.3　The power supply scope of a hydropower station should be determined by analyzing the development planning of local electric power system，scale of the hydropower station and its function in the system.

4.5.4　For a reservoir mainly operated for irrigation and water supply，when defining the installed capacity of the hydropower station，various alternatives of installed capacities shall be formulated on the basis of discharge duration of irrigation and water supply，and then finalized after techno-economic comparison.

4.5.5　For the selection of installed capacity，the flow rate to be abstracted by the hydropower station shall be coordinated with the upstream and downstream stations in the cascade.

4.5.6　The rated head of hydraulic turbines shall be determined according to the varying characteristics of water head and the weighted average water head of the hydropower station.For high-water-head diversiontype hydropower stations，the minimum head may be applied as the rated head；for other types of hydropower stations，the rated head may be selected between 0.85 and 0.95 based on the ratio of rated head to weighted average water head，and the rated head should not be higher than the weighted average water head in flood season.

4.5.7　For the selection of type and number of units for hydraulic turbines，several options shall be formulated to calculate the benefits and costs according to the hydropower station output，varying characteristics of water head，layout of the hydropower station complex，equipment manufacturing capability，and operational requirement of the electric power system，and then finalized after comprehensive analysis and comparison.The number of units should not be less than two to ensure safety and flexibility of the power system operation.

4.5.8　After the installed capacity of a hydropower station is selected，the effective energy output shall be calculated and analyzed，taking into consideration the balance of electric power and energy output of the system.For hydropower stations for which the balance of electric power and energy output is not considered，the effective energy output may be derived from the coefficient of effective energy output.