6.3　Cooling Water Supply and Drainage System

6.3　Cooling Water Supply and Drainage System

6.3.1　The mode of cooling water supply shall be defined based on the range of working heads of the hydropower station.If the minimum working head is lower than 15m，pump supply should be used；if the net head is between 15-100m，water should be supplied by gravity flow or gravity flow with a pressure-reducing device；if the net head is higher than 120m，water should be supplied by gravity flow with a pressurereducing device or by other methods.

If the range of working heads of a hydropower station is relatively wide while only one type of water supply cannot meet requirement or is not cost-effective，a mixed water supply mode may be adopted，and the division of the range of water heads for each kind of water supply mode shall be defined after technoeconomic comparison.

6.3.2　The cooling water supply system shall be able to work automatically.The water supply system by gravity flow with pressure reducing or by drawing water from the head cover shall be equipped with a pressure-relieving device.Measures shall be taken for maintenance and replacement of the first work gates for the pressured water drawing pipeline.

6.3.3　A standby water source for the main shaft seal of turbine should be available，and shall be able to start up automatically.

6.3.4　If water is supplied by pumps，a standby pump shall be prepared.If any pump in a set of pumps fails，the standby pump shall start up automatically.(https://www.daowen.com)

6.3.5　A water filter shall be installed for the cooling water supply system.During purifying work of the filter，the water supply for the system shall not be interrupted.The quality of water used for bearing lubrication and main shaft seal shall meet the requirements for water use by the units.

6.3.6　For service drainage and in-plant leakage drainage，drainage pumps should be equipped respectively.

Two service drainage pumps should be installed，and the total drainage volume shall guarantee that all deposited water from the overhaul of one unit can be drained thoroughly within 4-6h.The output flow of each pump shall be larger than the total leakage volume at the upstream and downstream gates.

There shall not be less than two drainage pumps for the in-plant leakage drainage sump，with at least one of them as the backup.The drainage pumps shall be operated automatically along with the variation of water levels in the drainage sump.

6.3.7　The drainage outdoors of the plant shall be an independent system，and shall not be diverted to the in-plant drainage sump or drainage gallery.