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

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UDC 621.65:62-531.3

Usachev A. P.

Method of estimating the efficiency of pumping unit frequency regulation (to be discussed)

Summary

The method of estimating energy saving from using frequency regulation of the pumping unit capacity in water supply systems is presented. The estimation of the capacity efficiency of pumping units is carried out only from the energy saving resulting from the use of frequency regulation instead of throttling (other saving components are not considered). To estimate energy saving it is required to compare the power consumed from the grid in the existing scheme of the regulation by penstock gate throttling and in the frequency regulation scheme. Then the energy saving in monetary form shall be compared with the expenses for retrofitting the frequency regulation system. The method is based on the graphical analysis of the pump operation point parameters in the operating group and optimized for the use in water supply systems operating by the pressure.

Key words

capacity , power saving , frequency regulation , pumping unit , efficiency evaluation , throttling

DOI 10.35776/MNP.2020.01.06
UDC 621.65:62-531.3

Usachev A. P.

Method of evaluating the effectiveness of frequency regulation of the performance of sewage pumping units

Summary

The method of evaluating energy savings through the use of frequency regulation of the pumping unit performance at sewage pumping stations is considered. The method is based on a graphical analysis of the parameters of the operation point of the pumps in the working group and is developed for the use in sewer networks that operate according to the level in the receiving tank. The proposed method of evaluating the effectiveness of frequency regulation at sewage pumping stations has been proved by many years of experience of using and is precisely evaluative. Energy savings at sewage pumping stations are significantly lower than at water pumping stations. This applies to the systems with start/stop control because the effect of frequency regulation consists in reducing the velocity of fluid in the pressure pipeline. The bigger the dynamic component of the network characteristic in relation to its static component (in the range of the station capacity change), the stronger effect is manifested. In practice, this is extremely rare. The energy savings in the above examples with the start/stop mode does not exceed 10% (excluding the losses in the frequency converter).

Key words

sewerage pumping station , power saving , frequency regulation , pumping unit , efficiency evaluation

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UDC 621.671.62-752

Shchavelev A. S.

The experience of establishing vibration diagnostics laboratory

Summary

The equipment life time includes the stage of maintenance and repair. Maintenance and repair control aims at reducing equipment outage and maintenance expenditures. Very often this stage is vitally important for industrial enterprises since maintenance expenditures are rather high. For the Russian enterprises maintenance and repair expenditures can reach 80% of the profit (the average value in USA and Western Europe is 25–30%). Nevertheless, even with these expenditures the failure rate in industry is too high. All the maintenance and repair expenditures are included into the water and sewerage tariff. Considering the social significance of tariff rates more transparent and reasonable repair process must be worked out. The control philosophy improvement, tools of technical control and diagnostics of the equipment condition provided for enhancing the efficiency of equipment maintenance and repair control. However, the operating experience shows that they did not gain widespread currency at the Russian industrial enterprises. In Tumen Vodokanal a vibration diagnostics laboratory has been established that carries out pumping unit vibration control and alignment at the company facilities. The conducted works ensured reducing pumping unit failures and improving the efficiency of cash flow distribution for the equipment repair.

Key words

rehabilitation , pumping unit , maintenance , vibration diagnostics , alignment , non-destructive control

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УДК 621.65:62–531.3:628.1/.2

Nikitin A. M., Balygin A. V., Shustova G. I., Iakovlev I. M.

Особенности частотного регулирования параллельно работающих насосов

Аннотация

Рассматривается один из вариантов энергоэффективной работы насосных агрегатов на насосных станциях водоснабжения и водоотведения при изменении частоты вращения рабочего колеса насоса с помощью частотно-регулируемых электроприводов, наиболее широко применяемых в современных условиях. Частотно-регулируемый электропривод устанавливается один на группу рабочих агрегатов или на каждый насос. Установка частотно-регулируемого электропривода на каждый рабочий агрегат является, на первый взгляд, довольно дорогостоящим мероприятием, поэтому чаще всего устанавливают один электропривод на группу (2–3 шт.) насосов. Однако при этом могут возникать кавитационные процессы, повышаться динамические нагрузки на подшипники и валы насосов, уменьшаться коэффициент полезного действия, и в конечном счете снижаться энергоэффективность работы насосов. По данным теоретического и практического обоснования, при установке частотно-регулируемых электроприводов на каждый рабочий насосный агрегат указанные выше недостатки сглаживаются, а энергоэффективность повышается.

Ключевые слова

pumping station , frequency-regulated electric drive , pumping unit , qualitative method of control , quantitative method of control , lifting efficiency

DOI 10.35776/MNP.2019.11.07
UDC 628.24:628.292:532.595.2

Zhitenev A. I., Kurganov Iu. A., IGNATCHIK V. S., Sarkisov S. V., Vinokurov Pavel

Results of experimental studies of water hammer arising in the operation of sewage pumping stations

Summary

The results of studies of water hammer arising in the operation of sewage pumping stations are presented. The studies were carried out at two stations of the same type in St. Petersburg. At present, there are no practical recommendations aimed at reducing the strength of water hammer at sewage pumping stations including the choice of location, type of check valves, a combination of their joint operation with smooth start, etc. Therefore, a set of experimental studies is conducted in St. Petersburg aimed at the solution to this problem. During the research, piezoresistor pressure transducers and a modular signal register were used. The use of check valves with hydraulic brakes is a more effective measure to combat water hammers compared to the smooth start and halt of the pumping unit. Water hammers that occur at the startup of pumping units while operating in combination with check valves without hydraulic brakes can exceed water hammers that occur when they stop.