2.5 Hydraulic Transition of Pumping Station

2.5.1

The water hammer of accident outage shall be calculated for the pumping station which is possible to produce hammer damage.The transient calculation shall be based on the different head and various operating conditions so as to determine the closing law of cutting-off device at the pump outlet reasonably.

2.5.2

When the pumps are suddenly powered off by accident,the guarantee value of maximum runaway speed rising ratio shall be selected according to the following different conditions:

1 For centrifugal pump,the speed shall not exceed 1.2 times of the rated speed.The duration shall not exceed 2min.

2 For mixed flow pump,the speed shall not exceed 1.5 times of the rated speed.The duration shall not exceed 2min.

3 For low-head axial flow pump,the speed shall not exceed 1.8 times of the rated speed.The duration shall not exceed 2min.

2.5.3

The highest pressure behind the service valve at the pump outlet shall not exceed 1.5 times of the pump outlet pressure.

2.5.4

When the guarantee value fails to meet Articles 2.5.2and2.5.3,technical and economic comparisons shall be performed and measures such as modifying the arrangement or size of the water conveyance system,increasing the pump unit rotational inertia,or setting a surge chamber shall be taken to rationally control the pressure rising ratio and the runaway speed.

2.5.5

For the pumping stations with multi-furcated inlet pipes and confluence outlet pipes,the maximum runaway speed and the maximum pressure rising ratio at the pump outlet shall be calculated in accordance with the possible number of units simultaneously powered off by accident,taking into account the num ber of units connected to the main outlet pipe and the mode of main electrical connection.All kinds of possible condition combinations may be considered in the calculation if necessary.

2.5.6

In the case of sudden starts or shuts down,the minimum pressure at the highest point in each section of the whole pressure water conveyance system shall not be less than 0.02MPa.Neither negative pressure nor separation flow shall be allowed.

2.5.7

For the long distance pressure water conveyance pen stock,the number and setting position of air valve shall meet the requirements of transient calculation.

2.5.8

For axial flow pumps,measures shall be taken to pre vent machine lifting.