МЕЖДУНАРОДНАЯ НАУЧНО-ТЕХНИЧЕСКАЯ КОНФЕРЕНЦИЯ
АКТУАЛЬНЫЕ ПРОБЛЕМЫ ЦИФРОВИЗАЦИИ ЭЛЕКТРОМЕХАНИЧЕСКИХ И
ЭЛЕКТРОТЕХНОЛОГИЧЕСКИХ СИСТЕМ
161
• Application of scientifically justified and technically feasible, progressive specific
power consumption standards for the pump station of machine water-lifting systems.
By the present time, in the practice of machine water lifting, only unregulated electric
drives are used as the drive for the pumping unit. In order to coordinate the water supply
mode of the pumping station with the water consumption schedule, the only practically
used method of regulating its performance at the moment is the adjustment of the number
of operating units, which provides for a stepped (per unit) regulation of the flow rate. In
most operating irrigation pumping stations, there is a mismatch between the actual water
consumption schedule and its coverage provided by the operation of the machine water
lifting system pumping station. Therefore, typically, in order to avoid crop yield losses of
field and garden crops, the machine water lifting pumping stations deliberately operate
with an inflated covering schedule, which in turn leads to unjustified overconsumption of
water resources and electrical energy. Another feature of the
operation of the machine
water lifting system pumping station is their conversion to a regulated electric drive
instead of an unregulated one, which will undoubtedly allow for the efficient use of
electrical energy and irrigation water, implement the transition to comprehensive
automation of the technological processes of water supply of pumping stations, increase
the flexibility of managing the load of electrical equipment, and increase the overall
operational resource of the energy and hydromechanical equipment of the pump unit.
In pump engineering practice, there are two fundamentally different methods of
regulating the performance (delivery) of a pumping unit:
• Quantitative – with constant speed (frequency) of the pump impeller, by changing
the characteristics of the discharge pipeline, the geometry of the pump flow passages, the
flow kinematics at the impeller inlet, etc.;
• Qualitative – by changing the speed (frequency) of the pump impeller.
The following methods of quantitative delivery regulation of the pumping unit can be
applied at the pump station of machine water lifting systems:
a) by using a throttling valve (throttling);
b) by diverting part of the water from the discharge pipeline to the suction
pipeline;
c) by introducing air
into the suction pipeline;
d) by changing the diameter of the impeller;
e) by adjusting the impeller blades or the guide apparatus.
It should be noted that the listed methods can only achieve pump performance
regulation mainly below its nominal delivery value.
Among the quantitative methods of pump delivery regulation mentioned by us,
throttle flow control has gained the widest application in the operation of small pumping
stations for machine water lifting systems, where it is necessary to regulate its
performance for a short period.
The advantages of throttle flow control include its simplicity, lack of need for
additional equipment, and the possibility of smoothly regulating the pump delivery within
the range from to zero.
The main disadvantages of throttling are its uneconomical nature due to increased
non-productive energy costs, a significant reduction in the efficiency of pumping
equipment, and accelerated wear of the valve, especially
when the water contains a
sufficient amount of abrasive particles in suspension and has a predominant turbidity,
which is typical for rivers and channels in most regions of our republic.
The regulation of the pump unit's supply by diverting a portion of the water can be
achieved by adjusting the opening of a valve installed on the bypass pipeline, through
which the required liquid flow is achieved by diverting it from the pressure pipeline to the
МЕЖДУНАРОДНАЯ НАУЧНО-ТЕХНИЧЕСКАЯ КОНФЕРЕНЦИЯ
АКТУАЛЬНЫЕ ПРОБЛЕМЫ ЦИФРОВИЗАЦИИ ЭЛЕКТРОМЕХАНИЧЕСКИХ И
ЭЛЕКТРОТЕХНОЛОГИЧЕСКИХ СИСТЕМ
162
suction pipeline. This method of regulating the water flow of the pump unit is mainly
used to eliminate unstable pump operation and is considered most appropriate in terms of
energy efficiency only for pumps with a specific speed coefficient (n) greater than 300,
where an increase in the pump unit's supply leads to a decrease in power on its shaft. In
centrifugal pumps with a lower specific speed coefficient, regulating the pump unit's
performance by diverting water leads to an increase in the pump's power. Consequently, it
causes an overload of the pump unit's drive motor. Despite improving the pump's
cavitation properties, this regulation method contributes to a decrease in its efficiency,
complicates the communication system, and increases the amount of equipment and the
overall size of the pump installation.
A more economical method than throttling is the regulation of the pump unit's supply
by admitting air into the suction pipeline. This method can be applied in cases where the
pump unit operates on an unbranched pressure network that
does not require special
devices to remove air, and the actual suction head for a particular pump model is
significantly less than the allowable value.
By introducing air into the suction pipeline, the pump's flow-head characteristic is
shifted downwards, while maintaining the values of the H characteristic, and the
intersection points determine the operating mode of the pumping unit. Thus, by varying
the amount of air entering the suction pipeline, it is possible to select the pump operating
mode that corresponds to the required delivery values of the pump unit. However, with an
increase in air content, despite the improved power consumption indicators of the pump
unit, its efficiency deteriorates due to the drop in head developed by the pump, and it also
provides a limited range of water delivery regulation, determined by the reduction in the
pump's cavitation qualities.
The method of regulating the delivery of the pump unit by trimming the pump
impeller on the outer diameter without changing the shape of its blades is mainly used in
pumping stations of machine water lifting systems equipped with identical pump
equipment, where there is a need to use a pump of this type with a lower power
consumption while providing the required delivery according to the pumping station
coverage schedule.
Typically, the maximum impeller trimming, taking into account its
speed coefficient, is no more than 11-15%, and in the practice of operating pumping
stations of machine water lifting systems, it is quite common to equip identical pump
units with pump equipment with different impeller diameters.
The considered method of regulating pump performance compared to throttling
provides significant power savings, has relatively high efficiency, and is most effective
for regulating the supply of a pump station in water lifting systems. However, regulating
the performance of a centrifugal pump by trimming its impeller diameter externally has
the drawback of fixing the pump supply at a constant level for a long period of time (until
the next overhaul period of the pump unit), as well as a limited range of flow rate
adjustment for the pump unit. Adjusting the performance of a pump unit by changing the
angle of the impeller blades is most effective in systems
with low static head and is
mainly implemented in axial and diagonal flow pumps. An analysis of the applied
methods of quantitative performance regulation of centrifugal pumps has shown that
throttling or direct pump intervention leads to a significant reduction in the energy
performance of the pump unit and sometimes complicates its design, shortens the service
life of the hydraulic equipment, and hinders the possibility of automating the water supply
process.
