Hydraulic calculation of group water intakes on underground wells equipped with pumps with variable speed drives

Summary

The use of variable speed drives at group water intakes on underground sources in water supply systems is aimed at saving electricity, ensuring efficient operation modes, improving the management engineering; however, without sufficient justification the desired result is not always effected. One of the reasons is the lack of calculation using an effective mathematical model that describes the movement of water in aquifers, wells, lift pipes and gathering mains, taking into account all the existing limitations, including the mode parameters while using variable speed drives in some or in all submersible pumps. The model is submitted in the form of an optimization task where the target function is the total power input of all the operating submersible pumps. The proposed optimization model provides for describing the modes of the group water intakes operating from the intake external boundary to the tanks. All the limitations of the optimization task can be divided into three non-overlapping groups as follows: balance, technologic, and performance ones. Having calculated the electricity consumption for all significant modes during the year and compared them with the costs at the existing modes without variable speed drives, we can make a reasonable conclusion about the applicability of a variable speed drive in one or more submersible pumps. The proposed model provides for arranging both efficient and technologically allowable operating modes.

Key words

frequency converter , water well , aquifer , submersible pump , hydraulic head , flow distribution task , optimization task , energy input , group water intake

Mathematical modeling of the joint operation of pumping units including frequency regulated ones

Summary

The use of pumping units with variable speed drives in order to save energy and provide for effective operating modes in water supply and sanitation systems, sometimes without sufficient justification, does not always furnish the desired result. One of the reasons is the lack of a simple mathematical model describing the flow distribution in the process pipelines of pumping stations with account of all the limitations of the operating mode parameters while using variable speed drives in some or all pumping units. The flow distribution task itself should be represented in the form of an optimization problem where the objective function can be the total energy input of all the operating pumping units. Such an optimization model provides for describing the operating modes of both paralleled and compound pumps. Once the electricity costs for all significant modes throughout the year have been determined and compared with the existing modes without the use of variable speed drives, drawing a reasonable conclusion about the applicability of variable speed drives in one or several pumping units becomes possible. The proposed model provides for arranging both effective and technologically acceptable modes. Based on the obtained results of calculating the optimization task for several modes, it is possible to construct approximating functions of the total flow of the pumping station from the head losses in throttling devices and use them in case of the flow meter lack or failure.

Key words

pressure , frequency converter , hydraulic head , centrifugal pump , pumping unit , flow distribution task , optimization task , energy input , parallel and serial operation of pumps