Technical water supply systems intaking water via tail water

A technical water supply systems intaking water via tail water intakes cooling water from the tail water for which power generation has been conducted by using a water pump and then sends the cooling water to the units.

In this system, a water pump is a device used to transfer the mechanical energy of the prime motor to the liquid so as to increase the energy of the liquid. For a power station, a water pump is one of the main devices which consume a lot of auxiliary power. As the operation efficiency of the power machine declines constantly, a high maintenance cost and intensive work are required.

Tianshengqiao No.2 Hydropower Station in Guizhou (H=220m，N=220MW×6) originally adopted two sets of systems for technical water supply and each of them is the backup system of the other. One of them supplies water via water pump pressurization and the other supplies water via automatic flow decompression. After the power station has been put into operation for a period, it is found that the water pump is started and then shutdown constantly with the starting and shutdown of the units. This causes two problems. One is that it causes a larger volume loss and easily brings into air which may cause operation failure to the water pump. The other is that it brings a higher operation and maintenance cost because the efficiency of the impeller of the water pump declines constantly due to cavitation and a great deal of electricity is used. Considering the stable and economical operation of the power station, the power station owner abandons the water supply system which supplies water via water pump pressurization and adopts the water supply system which supplies water via automatic flow decompression as the main water supply system.

Since the water supply system which supplies water via automatic flow decompression was adopted in 1996, no safety event had been caused by this system and no replacement had been conducted for the reducing valve in the last 10 years. This greatly lowers the operation cost and reduces the workload. This is also the case for many other power stations, for example, Zipingpu Hydro Power Station in Sichuan. According to the operation characteristic of a water pump, it is a common objective fact that the efficiency of a water pump declines with its operation time.