Studies of reliability indicators of pumping units of machine irrigation on the example of the “Namangan” pumping station

. The article presents the results of a reliability study, where violations of work are determined based on operational data to create a database for determining reliability indicators and the characteristics associated with them. The numbers of accidents, failures and defects of pumping units of the Namangan pumping station over a 5-year period are shown, and the values of the intensity of the occurrence of the event were calculated. By the method of statistical analysis of the safety of technical means at the stage of operation and analysis of the potentially emergency sequence, the most dangerous scenarios of the types are identified, the sequences of danger, causes, consequences and parameters to be monitored are determined, which will be useful for determining reliability, calculating risk and assessing the safety of pumping units and the pumping station itself. Taking into account that the uptime of pumping units of the PS of machine irrigation is distributed exponentially, the values of the probability of initial events are calculated and graphs of changes in the probabilities of initial events of work for 5 years, as well as work for 60 years PU are plotted.


Introduction
In terms of energy consumption, pumping stations of machine irrigation systems (РSМIS) are one of the most energy-intensive facilities in the region.The installed capacity of electrical equipment at РSМIS is more than 2,700 thousand kW with a consumption of 8 billion.kW of electricity or about 17% of the total amount of electricity consumed in the republic [1][2].
Irrigation of Uzbekistan in the course of its long development has formed into a complex diversified engineering system that provides water to the national economic complex of the republic, which includes more than 200 large irrigation systems, more than 30 reservoirs, hydraulic structures, pumping stations and wells [1,[3][4].
The constant growth of the areas of machine irrigation and reclamation lands on the basis of an increase in the number of electric pumping stations and wells, their capacities in the republic cause a steady increase in electricity consumption.The main consumers of electricity are pumping stations -the most energy-intensive part of the water sector.
Analysis of the water lifting schedule for the PS shows that the divergence of the water supply schedule from the possibility of pumping stations takes place 15-20%, which leads to overspending of electricity and irrigation water.The analysis of the state of NSSMO power consumption shows the presence of significant reserves of energy savings, reaching an average of up to 10%, and in some cases depending on the design features of pumping stations and their purpose [8][9][10].
At the present stage of operation of large irrigation pumping stations, the issues of reliability of electric machines are becoming more and more relevant.Thus, the technical level of operation of pumping stations is determined by the reliability and durability of electric machines during their operation.Reliability is the most important technical and economic indicator of an electric machine [11][12][13][14][15][16].Increasing the service life and increasing the reliability of machines give a relatively large economic effect along with improving other technical and economic indicators: efficiency, power factor, utilization factor, etc. [17][18][19][20].
The long-term operation of pumping units installed in irrigation pumping stations has led to a deviation of their technical characteristics from the factory and the appearance of undesirable phenomena -strong noises and vibrations.Vibration began to appear even in the building of the pumping station, which affects the state of the protection elements and automatic control of pumps, synchronous motors (SD), as well as the excitation system of the latter.As a result of unplanned outages, SD lead to disruption of uninterrupted water supply to consumers.Therefore, the task of quantifying the reliability of large SD and developing recommendations for improving durability is an urgent task [13][14][15].
As is known, there are two methods of reliability research: analytical and statistical [2].To study the reliability of the SD, the authors selected a statistical method that, based on operational and experimental data, determines the reliability indicators and the characteristics associated with them, depending on time, as well as the law of its distribution.
Here are the results of studies of the reliability of SD pumping units of the pumping station (NS) on the example of NS "Namangan".

Materials and methods
As is known, there are two methods of reliability research: analytical and statistical [1,2].To study reliability, the authors selected a statistical method that determines violations by operational means to create a database of determining reliability indicators and the characteristics associated with them.
The article presents the results of studies of violations of pumping units (РU) of the pumping station (PS) on the example of "Namangan".The PS was designed and put into operation in 1983, being the head part of the Great Namangan Canal in many ways determines the reliability, stability, safety and efficiency of the functioning of both the entire cascade and the multicomponent complex.In general, for the entire period of longterm operation (over 40 years) ensured the performance of its functions.Eight synchronous motors of the VDS2-325/69-16 type with the following nominal technical data are installed at this station: power -8.0 MW, stator voltage -10 kV, stator current -540 A, rotation speed -375 rpm.
At the same time, in the last period of work, a number of negative aspects have begun to manifest themselves, which have a noticeable impact on the reliability, safety and efficiency of the "Namangan" PS, due to both the design decisions taken and the processes of wear of equipment and structures, including due to the effects of water supply conditions, as well as restrictions on power supply caused by a shortage in the power unit of the electrical energy system and operating conditions .
In connection with the above, the purpose of this article was to create a database of violations that will be useful for determining the intensity of the occurrence of events, reliability, risk calculation and safety assessment of pumping units and the pumping station itself.

Results and discussion
To create a database of violations, the analysis of accidents, failures and defects that occurred was carried out on the example of large "Namangan" PS, and Figure 1 shows diagrams of the number of accidents, failures and defects of PS over a 5-year period. ...

Fig.1. Diagrams of the number of accidents, failures and defects of the "Namangan" PS
According to the data obtained, the values of the intensity of the occurrence of the event λ (1/ hour) were calculated, which are shown in Table 1.The analysis of the data in Table 1 shows that the main number of malfunctions, failures and partially inoperable condition is associated with a violation of the rotational support units and mechanisms of pumping units: shaft wear on all units (12%); destruction of the segments of the podpyatnik (12%); violation of the stuffing box seals of pumps (18%); temperature rise of the podpyatnik of the electric motor (7%); increased shaft fight (3%).
Failures of the mechanical part of the units can be explained by the beginning of wear processes, poor quality and non-compliance with the technology of capital, medium, routine repairs.Due to violations of the operating conditions provided for by the "Namangan" PS project, there were shutdowns due to strong vibration of the pumping unit No. 1 and a break in the power supply of unit No. 7.
At the "Namangan" PS, there were failures in the operation of an important node in the technological chain of water supply -3D160-115 type disc valves in the form of failures to close and open.On most pumping units, there are significant leaks through the disc valves on non-working units, reaching values up to 0.2 m 3 /s.Leaks on non-working units occur due to wear of rubber sealing parts of the disc valves and the presence of hydraulic connections in the combined systems of pressure pipelines.The cause of the malfunction is the wear of the rubber seal with a warranty period of no more than 6 years and no replacement.
Due to significant water leaks through the seals of the disc valves, the volume of water actually supplied to the discharge channel is less than the volume pumped from the supply channel, respectively, the efficiency of the pumping unit and the РS as a whole is reduced, the consumed electricity is inefficiently used.By the method of statistical analysis of the safety of technical means at the stage of operation and analysis of the potentially emergency sequence, the most dangerous scenarios of the types are identified.
The use of a functional-physical approach in conjunction with expert assessments of the degree of danger of potential emergency events allowed us to identify the parameters of individual components, processes to be monitored for diagnosing and ensuring the safety of NS, which is reflected in Fig. 2.These data can be useful in conducting a probabilistic safety analysis (PSA) of (PU) and calculating the risk and safety assessment at the station itself [5][6][7].Considering that the uptime of the SD pumping units of the РS machine irrigation is distributed exponentially [7], the probability values of the initial events P (t) are determined by the formula: P (t) = e -λt According to this formula, the values of the probabilities of the initial events are calculated and graphs of changes in P (t) over time for 1-5 years are plotted, taking into account operational data, where the values of the intensity of the occurrence of the event λ are taken from Tables 1 corresponding to the numbers of accidents, failures and defects, which are shown in Fig. From the analysis of the graphs, it can be concluded that the most reduction of probabilistic events (dangerous) are the following events: wear of the pump shaft and shutdown due to the destruction of the segments of the electric motor bearing (reduction of probabilistic events by -10.4%).
According to the formula (1), the theoretical values of the probabilities of the initial events during the work of 60 years are calculated and entered into Table 3.On the basis of the data of this table, graphs of changes in P (t) during the work of 60 years are constructed, where the values of the intensity of the occurrence of the event λ are taken from tables 1 corresponding to the numbers of accidents, failures and defects, which are shown 4.These data can effectively identify emergency factors, take the necessary emergency corrective measures aimed at improving the reliability of the pumping unit, which allows you to prevent an emergency.From the analysis of the graphs, it can be concluded that the most reduction of probabilistic events (dangerous) are the following events: wear of the pump shaft and shutdown due to the destruction of the segments of the electric motor bearing (reduction of probabilistic events by -82.4%).

Conclusions
1. From the analysis of the graphs of changes in the probabilities of the initial events P (t) over 5 years of work ON, it was concluded that the most decreasing probabilistic events (dangerous) are the events: wear of the pump shaft and shutdown due to the destruction of the segments of the electric motor bearing (a decrease in probabilistic events by -10.4%). 1.From the analysis of the graphs of changes in the probabilities of the initial events P (t) over 60 years of work ON, it was concluded that the most decreasing probabilistic events (dangerous) are the events: wear of the pump shaft and shutdown due to the destruction of the segments of the electric motor bearing (a decrease in probabilistic events by -82.4%).
3.The given databases can be used in determining reliability, calculating risk and assessing the safety of the pumping unit of the pumping station and the NS itself, for reliability control, allow you to calculate the risk, determine the severity of each violation and assess the safety of each element of the pumping unit and addressing each of them, display their states on the computer screen and effectively identify emergency factors, take the necessary emergency corrective measures aimed at improving the safety of the pumping unit, which allows you to prevent an emergency.

E3S 2023 Fig. 2 .
Fig. 2. Scheme for determining the sequence of hazards, causes, consequences and parameters to be monitored

2023 Table 2 .Fig. 3 .
Fig. 3. Graphs of changes in the probabilities of the initial events P (t)

Fig. 4 .
Fig. 4. Graphs of changes in the probabilities of the initial events P (t) during 60 years of work PU

Table 1 .
Types of accidents, failures and defects, their number and intensity of occurrence of the event

Table 3 .
The change in the probability of initial events of nodes and mechanisms