Hierarchical control vacuum system and transformer oil supplementing system and method

Abstract

The embodiment of the invention discloses a hierarchical control vacuum system and a transformer oil supplementing system and method.The system comprises an evacuation pipeline communicated with a transformer, two or more vacuum pumps communicated with the evacuation pipeline, two or more roots pumps located between the vacuum pumps and the transformer, and a vacuum pump communicated with the evacuation pipeline; the vacuum pump is matched with the roots pump to pump out the transformer, the pumping speed measuring device is communicated with the pumping pipeline and is used for measuring the pumping speed in the pumping pipeline, and the controller is electrically connected with the pumping speed measuring device and the roots pump and is used for receiving pumping speed data sent by the pumping speed measuring device. And when the pumping speed data is smaller than or equal to a preset pumping speed threshold value, part of the roots pumps and part of the vacuum pumps are controlled to be closed, and at least one vacuum pump and at least one roots pump are maintained to be vacuumized for a long time. The system can effectively reduce the energy consumption of long-time evacuation of the transformer.

Description

Technical Field

[0001] The embodiments of the present invention belong to the technical field of transformers, and particularly relate to a hierarchical control vacuum system, a transformer oil filling system and a method. Background Art

[0002] In the transformer industry, due to the product structure requirements, the evacuation and dehydration measures after the transformer is out of the furnace and assembled with moisture absorption are extremely important. All high-voltage and large-capacity products need to be evacuated to a full vacuum of 133 Pa or less and maintained for a long time to meet the normal insulation electrical performance.

[0003] Currently, when evacuating a transformer, the vacuum pumps used all require long-term evacuation. Each vacuum pump consumes a large amount of energy, and the number of vacuum pumps is large, so the energy consumption generated is even greater. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a hierarchical control vacuum system, a transformer oil filling system and a method in view of the above deficiencies in the prior art. The hierarchical control vacuum system can effectively reduce the energy consumption of long-term evacuation of the transformer.

[0005] According to an embodiment of the first aspect of the embodiments of the present invention, a hierarchical control vacuum system is provided, including: an evacuation pipeline, a vacuum pump, a Roots pump, a pumping speed measuring device and a controller; the evacuation pipeline is connected to the transformer, the number of vacuum pumps is two or more, the vacuum pumps are connected to the evacuation pipeline, the number of Roots pumps is two or more, the Roots pumps are located between the vacuum pumps and the transformer and are sequentially connected to the evacuation pipeline, the vacuum pumps and the Roots pumps cooperate to evacuate the transformer, the pumping speed measuring device is connected to the evacuation pipeline for measuring the pumping speed in the evacuation pipeline, and the controller is electrically connected to the pumping speed measuring device and the Roots pumps respectively, for receiving the pumping speed data sent by the pumping speed measuring device, and when the pumping speed data is less than or equal to a preset pumping speed threshold, controlling some of the Roots pumps and some of the vacuum pumps to be turned off, and maintaining at least one vacuum pump and at least one Roots pump for long-term evacuation.

[0006] In the embodiment of the present invention, the vacuum pump and the roots pump in the hierarchical control vacuum system cooperate to evacuate the transformer. As the vacuum degree increases, the pumping speed will naturally decay. Therefore, at the initial stage of vacuum pumping, more pumps are needed to maintain the pumping speed; as the vacuum pumping continues and the vacuum degree becomes larger, only a small part of the pumps need to be maintained to continue operating to meet the requirements of vacuum pumping. This system monitors the pumping speed in the evacuation pipeline in real time through a pumping speed measuring device; then, the controller dynamically adjusts the operating state of the pump group based on the pumping speed data sent by the pumping speed measuring device. Specifically, when the pumping speed is lower than the preset threshold, redundant roots pumps and some vacuum pumps are turned off, and at least one vacuum pump and at least one roots pump are maintained for long-term evacuation. That is to say, as the vacuum degree increases and the pumping speed naturally decays, the controller gradually cuts off the unnecessary subsequent roots pumps and redundant vacuum pumps according to the pumping speed threshold, and only retains the minimum pump group combination that meets the current pumping speed requirements, thereby avoiding the continuous operation of high-power equipment under inefficient working conditions, and then being able to effectively reduce the energy consumption of long-term evacuation of the transformer.

[0007] Optionally, the evacuation pipeline is provided with a main passage and evacuation branches. The number of evacuation branches is multiple. The multiple evacuation branches are connected in parallel with each other and are all connected to the main passage. The number of evacuation branches is the same as the number of vacuum pumps, and one vacuum pump is provided on each parallel branch.

[0008] Optionally, the evacuation pipeline further includes a first control valve. The number of first control valves is the same as the number of evacuation branches. One first control valve is provided on each evacuation branch. The first control valve is connected to the gas inlet end of the vacuum pump. The controller is electrically connected to the first control valve and is used to control some vacuum pumps to close and the corresponding first control valve to close when the pumping speed data is less than or equal to the preset pumping speed threshold, so that the corresponding evacuation branch is cut off.

[0009] Optionally, two or more roots pumps are connected in series on the main passage.

[0010] Optionally, the roots pump includes a primary roots pump and a secondary roots pump. The number of primary roots pumps is one, and the number of secondary roots pumps is at least one. The evacuation pipeline further includes bypass branches. The number of bypass branches is equal to the number of secondary roots pumps, and each bypass branch is connected in parallel with a secondary roots pump. The two ends of each bypass branch are respectively connected to the inlet end and the outlet end of the secondary roots pump; a second control valve is provided on each bypass branch.

[0011] Optionally, the controller is also electrically connected to the second control valve and is used to control the second control valve to open when the pumping speed data is less than or equal to the preset pumping speed threshold, so that the corresponding bypass branch is conducted.

[0012] Optionally, the hierarchical control vacuum system further includes a vacuum probe, which is connected to the evacuation pipeline. The vacuum probe is used to measure the vacuum degree in the evacuation pipeline. The controller is electrically connected to the vacuum probe and is used to receive the vacuum degree data sent by the vacuum probe. The controller is also used to control the start of each vacuum pump and each Roots pump according to the vacuum degree data and the preset vacuum degree permission start value.

[0013] Optionally, the vacuum degree permission start value of the vacuum pump is set as the first permission start value, the vacuum degree permission start value of the first-stage Roots pump is set as the second permission start value, and the vacuum degree permission start value of the secondary Roots pump is set as the third permission start value. The first permission start value, the second permission start value, and the third permission start value decrease in sequence. The controller is used to start the vacuum pump when the vacuum degree data is less than or equal to the first permission start value, start the first-stage Roots pump when the vacuum degree data is less than or equal to the second permission start value, and start the secondary Roots pump when the vacuum degree data is less than or equal to the third permission start value.

[0014] Optionally, the hierarchical control vacuum system further includes a transition tank, which is located between the evacuation pipeline and the transformer. The evacuation pipeline is connected to the transformer through the transition tank.

[0015] According to an embodiment of the second aspect of the present invention, a transformer oil replenishment system is provided, including: an oil replenishment device and the above-mentioned hierarchical control vacuum system. The controller of the hierarchical control vacuum system is electrically connected to the oil replenishment device and is used to control some of the Roots pumps and some of the vacuum pumps to close when the pumping speed data is less than or equal to a preset pumping speed threshold, maintain at least one vacuum pump and at least one Roots pump for long-term evacuation, and send a start signal to the oil replenishment device. The oil replenishment device is used to replenish oil to the transformer according to the start signal.

[0016] According to an embodiment of the third aspect of the present invention, a method for evacuating a transformer is provided, using the above-mentioned hierarchical control vacuum system. The method includes:

[0017] Evacuating the transformer through a vacuum pump and a Roots pump,

[0018] Measuring the pumping speed in the evacuation pipeline to obtain pumping speed data,

[0019] When the pumping speed data is less than or equal to a preset pumping speed threshold, controlling some of the Roots pumps and some of the vacuum pumps to close and maintaining at least one vacuum pump and at least one Roots pump for long-term evacuation.

[0020] Optionally, evacuating the transformer through a vacuum pump and a Roots pump includes: obtaining the pumping speed data and the vacuum degree permission start value in the evacuation pipeline,

[0021] The allowable starting values of the vacuum degree include: the first allowable starting value, the second allowable starting value, and the third allowable starting value, and the first allowable starting value, the second allowable starting value, and the third allowable starting value decrease in sequence.

[0022] When the vacuum degree data is less than or equal to the first allowable starting value, start the vacuum pump and evacuate through the vacuum pump.

[0023] When the vacuum degree data is less than or equal to the second allowable starting value, start the primary Roots pump in the Roots pump and evacuate through the vacuum pump and the primary Roots pump together.

[0024] When the vacuum degree data is less than or equal to the third allowable starting value, start the secondary Roots pump in the Roots pump and evacuate through the vacuum pump, the primary Roots pump, and the secondary Roots pump together.

[0025] Optionally, when the pumping speed data is less than or equal to a preset pumping speed threshold, control some of the Roots pumps and some of the vacuum pumps to close, and maintain at least one vacuum pump and at least one Roots pump for long-term evacuation. Specifically:

[0026] When the pumping speed data is less than or equal to a preset pumping speed threshold, maintain one of the vacuum pumps in operation and close the remaining vacuum pumps, and maintain the primary Roots pump in operation and close all the secondary Roots pumps. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of a hierarchical control vacuum system in some embodiments of the embodiments of the present invention.

[0028] In the figure: 1. Evacuation pipeline; 11. Main passage; 12. Evacuation branch; 13. Bypass branch; 14. Air flow direction; 2. Vacuum pump; 21. First vacuum pump; 22. Second vacuum pump; 3. Roots pump; 31. Primary Roots pump; 32. Secondary Roots pump; 4. First control valve; 41. First branch valve; 42. Second branch valve; 5. Second control valve; 6. First main passage valve; 7. Second main passage valve; 8. Vacuum gauge; 9. Pumping speed measuring device; 10. Transition tank; 110. Transformer. Detailed Embodiments

[0029] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the scope of the present invention.

[0030] In the description of the embodiments of the present invention, it should be noted that the terms "upper", "lower", "upstream", "downstream", etc. indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings. These are only for the convenience of description and simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the embodiments of the present invention.

[0031] In the description of the embodiments of the present invention, the terms "first", "second", "third" are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0032] In the description of the embodiments of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "connected", "arranged", "installed", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific situations.

[0033] First of all, it should be noted that in this application document, the degree of vacuum refers to the absolute pressure value of the vacuum system. The smaller the value, the higher the degree of vacuum (that is, closer to the absolute vacuum state). The pumping speed refers to the volume of gas pumped out by the vacuum pump from the container to be pumped per unit time, and the unit is m3 / h. Since the gas density decreases as the degree of vacuum increases (the pressure decreases), the pumping speed will show a natural attenuation characteristic.

[0034] It also needs to be noted that in the transformer industry, due to the requirements of the product structure, the evacuation and dehydration measures after the transformer is out of the furnace and assembled and absorbs moisture are extremely important. All high-voltage and large-capacity products need to be evacuated to a full vacuum of 133 Pa and below and maintained for a long time to meet the normal insulation electrical performance. On the one hand, the long-time evacuation process takes a long time for the vacuum equipment. Since the vacuum pumps usually used are composed of two-stage or more multi-stage vacuum pumps and the number of vacuum pumps is large, during the vacuum pumping process, there will inevitably be more energy consumption and equipment losses due to the long-time operation of the multi-stage high-power vacuum pumps from the beginning to the end, increasing unnecessary waste. Therefore, it is necessary to analyze, study and improve the vacuum pumps, pumping speed, degree of vacuum and their mutual working characteristics and structural characteristics during the transformer vacuum process in order to solve and improve the above various problems.

[0035] For the irrationality and non-necessity that all vacuum pumps in the existing vacuum system need to operate throughout the long-time full-vacuum pumping process, technical addition, structural adjustment and control improvement are carried out so that it can not only meet the working characteristics of each stage of the vacuum pump, but also meet the evacuation needs and quality requirements and reach the most economical operating condition requirements.

[0036] In this application, a hierarchical control vacuum system is proposed. This hierarchical control vacuum system is applicable to various scenarios that require long-term evacuation, especially in the field of transformer manufacturing technology. More specifically, it is applicable to large transformers that are evacuated to full vacuum for vacuum oil injection.

[0037] Embodiment 1

[0038] Please refer to Figure 1 , an embodiment of the present invention discloses a hierarchical control vacuum system, which is mainly used in a transformer system and includes: an evacuation pipeline 1, a vacuum pump 2, a roots pump 3, a pumping speed measuring device 9, and a controller.

[0039] Among them, the evacuation pipeline 1 is connected to the transformer 110. The number of vacuum pumps 2 is two or more, and the vacuum pumps 2 are connected to the evacuation pipeline 1. The number of roots pumps 3 is two or more, and the roots pumps 3 are located between the vacuum pumps 2 and the transformer 110 and are connected to the evacuation pipeline 1. The vacuum pumps 2 and the roots pumps 3 cooperate to evacuate the transformer 110. The pumping speed measuring device 9 is connected to the evacuation pipeline 1 and is used to measure the pumping speed in the evacuation pipeline 1. The pumping speed measuring device 9 can adopt an existing flow meter. The controller is electrically connected to the pumping speed measuring device 9 and the roots pumps 3 respectively, and is used to receive the pumping speed data sent by the pumping speed measuring device 9, and when the pumping speed data is less than or equal to a preset pumping speed threshold, control some of the roots pumps 3 and some of the vacuum pumps 2 to close, and maintain at least one vacuum pump 2 and at least one roots pump 3 for long-term evacuation.

[0040] First, it is necessary to explain the working characteristics of the vacuum pump 2 and the roots pump 3: The vacuum pump 2 can be started at atmospheric pressure, and the roots pump 3 needs to be pre-evacuated to a certain vacuum degree by a fore pump before it can be started. Otherwise, it may be damaged due to overload. The roots pump 3 has higher efficiency in the high vacuum stage, and the vacuum pump 2 needs to cooperate with the roots pump 3 to meet the evacuation requirements of high vacuum. Therefore, this hierarchical control vacuum system needs to cooperate the vacuum pump 2 with the roots pump 3 to finally obtain a high vacuum. The pumping speed and ultimate vacuum degree of the single vacuum pump 2 cannot meet the evacuation requirements.

[0041] Furthermore, a plurality of vacuum pumps 2 and Roots pumps 3 are arranged in the evacuation pipeline 1, and a pumping speed measuring device 9 is provided to monitor the pumping speed of the pipeline in real time. The controller dynamically adjusts the operation state of the pump group based on the pumping speed data. When the pumping speed is lower than the preset threshold, the redundant Roots pumps 3 and vacuum pumps 2 are sequentially shut down. Specifically, in the initial stage of vacuum pumping, all the vacuum pumps 2 and Roots pumps 3 operate in coordination to quickly establish a high pumping speed to shorten the initial evacuation time. As the vacuum degree increases and the pumping speed naturally decays, the controller gradually cuts off the unnecessary subsequent Roots pumps 3 and redundant vacuum pumps 2 according to the pumping speed threshold, and only retains the minimum pump group combination that meets the current pumping speed requirement, such as a single vacuum pump 2 and a single Roots pump 3 (the first-stage Roots pump 31), so as to avoid the continuous operation of high-power equipment under inefficient working conditions. This dynamic regulation mechanism enables the system to maintain a high vacuum while significantly reducing the operation time and energy consumption of the subsequent Roots pumps 3 and redundant vacuum pumps 2, and finally realizes the improvement of the comprehensive energy efficiency during the long-time evacuation process.

[0042] It should also be noted that the hierarchical control vacuum system is implemented based on the following principle: in the system, as the vacuum degree increases, the pumping speed will exhibit a natural decay characteristic. Specifically, as the vacuum degree increases (the pressure in the space decreases), the gas density decreases exponentially, resulting in a synchronous decay of the gas volume that can be evacuated per unit time. The relationship between the effective pumping speed Q and the theoretical pumping speed S of the pump is: Q = S × P; obviously, in the high-vacuum stage (for example, P < 1000 Pa), the actual effective pumping speed Q will be significantly lower than the theoretical maximum value of the pump. This solution dynamically reduces the number of redundant pumps in operation, so that the system's pumping speed requirement always matches the current Q value, thereby avoiding energy waste.

[0043] Furthermore, during the vacuum pumping process of the transformer 110, through the development of the hierarchical adaptive vacuum system, combined with the corresponding change characteristics of the pumping speed and vacuum degree allowed by each stage of the vacuum pump 2 during the operation of the pre-set vacuum system and the participation of the control system, during the process of evacuating the transformer 110 from normal pressure to high vacuum, every time a pumping speed control point of the combination of vacuum pumps 2 is reached, the associated vacuum pump 2 (or Roots pump 3) is automatically cut off accordingly, and so on until the vacuum pumping process under the matching of the single combination with the minimum pumping speed. The developed hierarchical control vacuum system provides structural improvement and technological progress for the high-vacuum and long-time vacuum pumping process of the large transformer 110, and at the same time provides an economical and long-life solution, which is extremely important and significant during the production process of the transformer 110.

[0044] In this embodiment, the pumping speed threshold is 99% of the rated pumping speed of the secondary Roots pump 32, which can be appropriately adjusted specifically (should be specific to the actual usage situation and finally determined through debugging). Exemplarily, when the measured pumping speed is lower than 99% of the effective pumping speed of the secondary Roots pump 32 (for example, the rated pumping speed of 2000 m3 / h corresponds to a threshold of 1980 m3 / h), the bypass pipeline is switched to prevent misoperation caused by the measurement deviation between the displayed pumping speed and the actual pumping speed.

[0045] In summary, this hierarchical control vacuum system monitors the pumping speed in the evacuation pipeline 1, and gradually cuts off the unnecessary subsequent Roots pumps 3 and redundant vacuum pumps 2 according to the pumping speed threshold, only retaining the minimum pump group combination that meets the current pumping speed requirements, thereby effectively reducing the energy consumption for the long-term evacuation of the transformer 110.

[0046] The hierarchical control vacuum system in this embodiment combines the characteristics and relationship curves of the changes in pumping speed and vacuum degree as the gas inside the transformer 110 decreases during the operation of the vacuum system, that is, the smaller the vacuum degree, the smaller the pumping speed (here, the smaller the vacuum degree means the smaller the numerical value of the gas pressure; the smaller the numerical value of the gas pressure, the higher the vacuum degree, that is, the closer it is to the vacuum state in the transformer 110), as well as the vacuum requirements that the vacuum pump 2 and the Roots pump 3 must reach and meet during their own startup and operation and the change characteristics finally measured by the pumping speed measuring device 9. Through the structural analysis of the existing evacuation system for large transformers 110 configured with at least three-stage vacuum pumps (that is, the vacuum pump 2, the primary Roots pump 31, and the secondary Roots pump 32). The overall innovative technologies are as follows:

[0047] 1. The hierarchical adaptive vacuum system for the transformer 110 consists of: vacuum pumps (two or more), a primary Roots pump 31, a secondary Roots pump 32 (including: a secondary Roots pump 3, a tertiary or multi-stage Roots pump 3), a bypass pipeline and control valves, a pumping speed measuring device 9, a vacuum gauge 8, a control cabinet, etc.

[0048] 2. A pumping speed measuring device 9 and a vacuum probe are added to the inlet of the vacuum system to meet the detection of pumping speed and vacuum degree during the evacuation process of the transformer 110, so as to perform relevant data acquisition and participate in control.

[0049] 3. According to the evacuation requirements of the vacuum system, the front-stage vacuum pumps are reasonably combined in a manner of at least two or more vacuum pumps running in parallel, and isolation control valves are added to the vacuum pumps for reasonable switching and economic operation during subsequent hierarchical control.

[0050] 4. A bypass pipeline and control valve structure are added to the secondary, tertiary or more-stage Roots vacuum pumps (i.e., Roots pumps) except for the front-stage vacuum pumps in the vacuum system, so as to gradually reduce the input of vacuum pumps during the vacuum pumping process in combination with the change process of vacuum degree and pumping speed.

[0051] 5. When the hierarchical control vacuum system evacuates the transformer 110 main body, under the configuration conditions of the fore-vacuum pump, the first-stage roots vacuum pump (i.e., the first-stage roots pump), and the second-stage roots vacuum pump (i.e., the second-stage roots pump), when evacuating, first all the isolation valves of the fore-vacuum pumps 2 are fully opened, and all the bypass pipelines of the subsequent roots vacuum pumps (i.e., the roots pumps) are fully closed. During normal startup and evacuation, all the vacuum pumps 2 are started step by step and evacuate the transformer 110. As the evacuation process continues, the vacuum degree of the vacuum system becomes smaller and smaller (here, the smaller the vacuum degree mentioned, the smaller the value of the gas pressure; the smaller the gas pressure value, the higher the vacuum degree, that is, the closer the transformer 110 is to the vacuum state), and the pumping speed becomes lower and lower. When the pumping speed of the system is lower than a certain value of the effective pumping speed of the first-stage roots pump 31, the bypass pipeline valve of the second-stage roots pump 3 is automatically opened, and the operation of the second-stage roots pump 3 and the closing of the inlet valve are stopped; correspondingly, the fore-vacuum pump 2 is automatically matched to the structure of the vacuum pump 2 + the first-stage roots pump 31 according to the pumping speed requirement of the first-stage roots pump 31, and then continues the normal operation of the evacuation process with the most economical need.

[0052] 6. When the hierarchical control vacuum system conducts vacuum oil filling for the transformer 110 and evacuates the small-space components, this set of vacuum oil filling mode of the system can be directly adopted. When in need of use, only need to switch the program to the vacuum oil filling mode, and it will automatically close the valve at the front end of one of the two vacuum pumps 2 (the correspondence can be set in advance), open the bypass valve of the second-stage roots pump 3, and close the valve at its inlet end. After startup, a vacuum system with only one vacuum pump 2 and one first-stage roots pump 31 running is realized, so that it can not only meet the need of vacuum oil filling, but also realize the state where the second-stage roots pump 3 does not need to participate in the work, achieving energy consumption saving and loss reduction.

[0053] 7. Realization of the control process: The above realization process is set, displayed in real time, and controlled through the control system, and at the same time has the functions of data storage and transmission, meeting the requirements of digital production. To ensure the smooth operation of the above process, a set of effective technical methods for mutual recognition of vacuum degree and rotational speed need to be formed through special verification in combination with the product structure. It is mainly manifested in the following aspects.

[0054] 7.1. The associated control of the startup, operation, and stop processes of each stage of the vacuum pump 2 with the corresponding pumping speed, vacuum degree, and branch and bypass control valves. And the control system is programmed and set in combination with the above control process, and finally the automatic operation of the hierarchical control vacuum system and the evacuation application of various transformers 110 are realized.

[0055] 7.2. Under the above conditions, a control system is established. Through the vacuum degree, pumping speed, valves, etc. set in advance by the control system, it can be switched in stages according to the above control process to realize the established evacuation need of the transformer 110 and the economical operation of the vacuum system.

[0056] Please continue to refer to Figure 1 In some embodiments, the evacuation pipeline 1 is provided with a main passage 11 and evacuation branches 12. The number of evacuation branches 12 is multiple. The multiple evacuation branches 12 are connected in parallel with each other and are all connected to the main passage 11. The number of evacuation branches 12 is the same as the number of vacuum pumps 2. A vacuum pump 2 is arranged on each parallel branch.

[0057] That is to say, in this embodiment, multiple parallel vacuum pumps 2 are configured on the evacuation pipeline 1. Exemplarily, Figure 1 shows the case where two vacuum pumps 2 are connected in parallel. By providing multiple parallel evacuation branches 12 with the same number as the vacuum pumps 2, each vacuum pump 2 can be independently configured on a single branch and controlled by an isolation valve. At the initial stage of vacuum pumping, the superimposed pumping speed can be provided through the parallel operation of all pumps (for example, the double-pump parallel pumping speed reaches 2000 m3 / h), and the large-flow pumping of the pre-stage can be quickly completed; while in the middle and late stages of the vacuum degree improvement, by closing the redundant branches (such as only retaining the single-pump operation), the current low pumping speed requirement (such as 500 m3 / h) can be accurately matched, thereby avoiding the energy waste caused by the inefficient operation of multiple pumps.

[0058] In addition, it should be noted that, compared with directly using a single large-pumping-speed vacuum pump 2, in this system, multiple parallel vacuum pumps 2 are configured on the evacuation pipeline 1. The advantage is that it can dynamically adapt to different pumping speed requirements and achieve efficient operation under all working conditions. Specifically, for the vacuum pump 2, there is an efficient operation range (for example: within the range of 80-100% of the rated power, the operation efficiency of the vacuum pump 2 is relatively good). In the stage of low pumping speed, if a single large-pumping-speed pump is used for variable-frequency speed regulation to match the pumping speed required by the system, it means that the large-pumping-speed pump can only run idly, and at this time, the operation efficiency of the pump will drop significantly. Multiple pumps in parallel can run at full power in the stage of high pumping speed demand (such as the initial vacuum pumping stage) (for example, the double-pump superimposed pumping speed is 2000 m3 / h), and only a single pump (500 m3 / h) is enabled in the stage of low pumping speed (such as the vacuum maintenance stage), so that each pump always runs in the high-efficiency load range.

[0059] In addition, the independent control characteristic of the parallel branches enables the corresponding branch to be quickly isolated when a single pump fails, ensuring the continuous operation of the remaining pump groups and significantly improving the operation reliability and maintenance convenience of the system.

[0060] Furthermore, the evacuation pipeline 1 further includes first control valves 4. The number of first control valves 4 is the same as the number of evacuation branches 12. A first control valve 4 is arranged on each evacuation branch 12. The first control valve 4 is connected to the gas inlet end of the vacuum pump 2. The controller is electrically connected to the first control valve 4 and is used to control the closing of some vacuum pumps 2 and the corresponding first control valves 4 when the pumping speed data is less than or equal to the preset pumping speed threshold, so as to cut off the corresponding evacuation branch 12.

[0061] As Figure 1 shown, by setting a first control valve 4 at the gas inlet end of the vacuum pump 2 in each evacuation branch 12 and making it controlled by the controller, this solution realizes the precise shutdown of the redundant vacuum pump 2 branch. Specifically, when the pumping speed data is lower than the preset threshold, the controller synchronously closes the vacuum pump 2 in the corresponding branch and the first control valve 4 set at its gas inlet end, completely cutting off the gas flow channel of this branch. On the one hand, this design avoids the idling loss of the vacuum pump 2 after shutdown caused by the backflow of residual gas in the pipeline. On the other hand, it prevents the interference of the closed branch on the flow field of the main passage 11 through physical isolation, ensuring that the remaining operating pump group is always in the efficient working range.

[0062] Please refer to Figure 1 , in some embodiments, two or more roots pumps 3 are connected in series on the main passage 11.

[0063] As described above, the vacuum pump 2 can be started at atmospheric pressure, and the roots pump 3 needs to be pre-evacuated to a certain vacuum degree by a fore pump before it can be started. Otherwise, it may be damaged by overload; while the roots pump 3 has higher efficiency in the high vacuum stage, and the vacuum pump 2 needs to cooperate with the roots pump 3 to meet the evacuation requirements of high vacuum degree.

[0064] By connecting multiple roots pumps 3 in series on the main passage 11, this system constructs a gradient pumping structure with multi-stage compression. Specifically, the front-stage roots pump 3 pre-compresses the gas to the intermediate pressure range (for example: 5000 - 1000 Pa), and the rear-stage roots pump 3 further compresses it to the high vacuum target value (for example < 133 Pa) based on the output pressure of the front stage.

[0065] This series design enables each stage of the roots pump 3 to always operate in its high-efficiency pressure range (such as the first-stage roots pump 31 has an efficiency of 85% at 5000 - 1000 Pa, and the second stage has an efficiency of 80% at 1000 - 100 Pa). Compared with the working condition of a single-stage roots pump 3 directly compressing to the ultimate vacuum (the efficiency drops suddenly to less than 50%), the overall energy efficiency of the system is improved by 30% - 40%. In addition, the series structure reduces the single-pump load through pressure grading (such as the inlet pressure of the second-stage pump drops from atmospheric pressure to 1000 Pa, and the power consumption is reduced by 25%), and at the same time avoids the risk of single-pump overload, significantly extending the service life of the equipment.

[0066] Furthermore, the Roots pump 3 includes a primary Roots pump 31 and a secondary Roots pump 32. The number of primary Roots pumps 31 is one, and the number of secondary Roots pumps 32 is at least one. The evacuation pipeline 1 further includes a bypass branch 13. The number of bypass branches 13 is equal to the number of secondary Roots pumps 32, and each bypass branch 13 is connected in parallel with a secondary Roots pump 32. Both ends of the bypass branch 13 are respectively communicated with the inlet end and the outlet end of the secondary Roots pump 32; a second control valve 5 is provided on each bypass branch 13.

[0067] It should be noted that the secondary Roots pump here includes the next-level Roots pump (i.e., the second-level Roots pump), the next-next-level Roots pump (i.e., the third-level Roots pump), …, and even the last-level Roots pump. Taking the number of Roots pumps as four levels as an example, among them, from the direction gradually away from the vacuum pump, the four-level Roots pumps are respectively the primary Roots pump, the next-level Roots pump (i.e., the second-level Roots pump), the next-next-level Roots pump (i.e., the third-level Roots pump), and the last-level Roots pump (i.e., the fourth-level Roots pump). For the convenience of description, in this embodiment, the next-level Roots pump, the next-next-level Roots pump, and the last-level Roots pump are collectively referred to as the secondary Roots pump.

[0068] In this embodiment, the controller is also electrically connected to the second control valve 5, and is used to control the second control valve 5 to open when the pumping speed data is less than or equal to a preset pumping speed threshold, so that the corresponding bypass branch 13 is conducted.

[0069] By configuring the bypass branch 13 and the second control valve 5 for each secondary Roots pump 32, the system can realize the dynamic cut-out of the rear-stage Roots pump 3 and the optimization of the air flow path.

[0070] Specifically, when the pumping speed drops below the effective working range of the secondary Roots pump 32, the controller opens the second control valve 5 of the bypass branch 13 and closes the secondary Roots pump 32, so that the air flow directly bypasses the pump body. On the one hand, it can eliminate the flow resistance loss after the secondary pump is shut down; on the other hand, it can avoid the rotor idling wear caused by gas reflux in the shut-down pump.

[0071] In addition, the independent control characteristic of the bypass branch 13 ensures that in the high-vacuum stage, the hierarchical control vacuum system can still maintain a stable pumping speed through the fore pump and the primary Roots pump 31, while completely avoiding the ineffective operation of the secondary pump in the low-efficiency interval, thereby realizing the coordinated improvement of energy efficiency and equipment life.

[0072] In some embodiments, the hierarchical control vacuum system further includes a vacuum probe. The vacuum probe is connected to the evacuation pipeline 1 and is used to measure the vacuum degree inside the evacuation pipeline 1. The controller is electrically connected to the vacuum probe and is used to receive the vacuum degree data sent by the vacuum probe. The controller pre-sets the vacuum degree permission start values of each vacuum pump 2 and each Roots pump 3, and the controller is further used to sequentially control the start of each vacuum pump 2 and each Roots pump 3 according to the vacuum degree data and the pre-set vacuum degree permission start values.

[0073] Further, the vacuum degree permission start value of the vacuum pump 2 is set as the first permission start value, the vacuum degree permission start value of the primary Roots pump 31 is set as the second permission start value, and the vacuum degree permission start value of the secondary Roots pump 32 is set as the third permission start value. The first permission start value, the second permission start value, and the third permission start value decrease in sequence. The controller is used to start the vacuum pump 2 when the vacuum degree data is less than or equal to the first permission start value, start the primary Roots pump 31 when the vacuum degree data is less than or equal to the second permission start value, and start the secondary Roots pump 32 when the vacuum degree data is less than or equal to the third permission start value.

[0074] Exemplarily, the first permission start value (for the vacuum pump 2): atmospheric pressure; the second permission start value (for the primary Roots pump 31): 5000 - 3000 Pa; the third permission start value (for the secondary Roots pump 32, which may include the second-stage Roots pump 3, the third-stage Roots pump 3, and even multi-stage Roots pumps 3): 2000 - 800 Pa.

[0075] The following is the start-up process of this hierarchical control vacuum system:

[0076] First of all, it is necessary to explain the working characteristics of the vacuum pump 2 and the Roots pump 3: The vacuum pump 2 can be started at atmospheric pressure. The Roots pump 3 needs to be pre-evacuated to a certain vacuum degree by the fore-pump before it can be started. Otherwise, it may be damaged due to overload. And the Roots pump 3 has higher efficiency in the high-vacuum stage. The vacuum pump 2 needs to cooperate with the Roots pump 3 to meet the evacuation requirements of high vacuum degree. That is to say, it is necessary to cooperate the vacuum pump 2 with the Roots pump 3 to finally obtain high vacuum. The pumping speed and ultimate vacuum degree of the single vacuum pump 2 cannot meet the evacuation requirements.

[0077] When this hierarchical control vacuum system is started, first evacuate through the vacuum pump 2. When the vacuum degree in the system reaches the start-up requirement of the Roots pump 3, then start each stage of the Roots pump 3 in sequence. In other words, the fore-pump (vacuum pump 2) creates the start-up condition for the Roots pump 3, and the Roots pump 3 boosts the vacuum degree by relay.

[0078] In some embodiments, the hierarchical control vacuum system further includes a transition tank 10. The transition tank 10 is located between the evacuation pipeline 1 and the transformer 110, and the evacuation pipeline 1 is connected to the transformer 110 through the transition tank 10.

[0079] By setting up a transition tank 10 between the evacuation pipeline 1 and the transformer 110, the air flow buffering and process optimization of the vacuum evacuation process can be achieved. As an intermediate container, the transition tank 10 can temporarily store a large amount of rapidly discharged gas at the initial stage of vacuum evacuation, avoiding the direct impact of air flow pulses on the vacuum pump 2 sets, reducing the pressure fluctuation at the pump inlet, and significantly improving the operation stability of the pump sets.

[0080] The following further explains this hierarchical control vacuum system:

[0081] This hierarchical control vacuum system is mainly applied in the field of vacuum evacuation of the transformer 110 that must be within the full vacuum range and maintain a certain evacuation time during vacuum evacuation.

[0082] This new technology includes a vacuum pump 2 (two or more), a primary Roots pump 31, a secondary Roots pump 3, a tertiary or multi-stage Roots pump 3, a pumping speed measuring device 9, bypass pipelines and control valves for each subsequent vacuum pump 2, isolation control valves for multiple primary vacuum pumps 2 at the front stage, a vacuum gauge 8, a control system, and a data transmission system. A pumping speed detection device and a vacuum degree detection are added at the inlet end of the vacuum system to continuously detect the pumping speed and vacuum degree when the vacuum system is working. In a multi-stage vacuum system, bypass pipelines and control valves are added to other hierarchical vacuum pumps 2 except the primary vacuum pump 2 at the front stage, so as to cut off and bypass isolate step by step from the back to the front when necessary for the pumping speed and vacuum degree. Isolation control valves are added to the branches of multiple primary vacuum pumps 2 in the multi-stage vacuum system to correspondingly cut off the unnecessary number of primary vacuum pumps 2 in the case of a smaller pumping speed and a high vacuum after the subsequent vacuum pump 2 is removed, reducing unnecessary losses.

[0083] The hierarchical control vacuum system and its application method are combined with the design requirements of the evacuation rate and vacuum degree of the transformer 110. The primary and subsequent vacuum pumps 2 are reasonably matched and structurally designed according to the hierarchical and adaptive vacuum technology requirements. At the same time, combined with the optimized combination relationship of the primary and subsequent vacuum pumps 2, setting parameters under different pumping speeds and vacuum degrees are provided. During the evacuation process, combined with the relationship curve of the change of vacuum degree and pumping speed, and the characteristics of the primary and subsequent vacuum combinations, as the evacuation process progresses, the pumping speed of the vacuum system becomes lower and lower, and the vacuum degree becomes smaller and smaller. During this process, when the pumping speed of the system is lower than a certain value of the effective pumping speed of the last-stage Roots pump 3, the bypass pipeline valve of the last-stage Roots pump 3 is automatically opened, the operation of the last-stage Roots pump 3 is stopped, and this path is cut out; correspondingly, the number of matched primary vacuum pumps 2 is automatically reduced according to the pumping speed requirements of the second-to-last-stage Roots pump 3, and so on until the evacuation process under the single combination matching of the minimum pumping speed. The entire process is automatically detected and switched, without manual intervention, and always operates normally during the evacuation process with the most economical structure and evacuation needs.

[0084] When the hierarchical control vacuum system directly adopts the vacuum oil filling mode during the vacuum oil filling of the transformer 110 and the evacuation of components in a small space, it will automatically close the valve at the front end of one of the two vacuum pumps 2 (the correspondence can be set in advance), open the bypass valve of the last-stage Roots pump 3, and close the valve at its inlet end. After starting, a vacuum system with only one vacuum pump 2 and one Roots pump 3 running is achieved.

[0085] Establishment of the control program: Combining the structural characteristics and technical requirements of the above-mentioned adaptive hierarchical vacuum system, the control system is programmed and set to finally meet the adaptive matching of hierarchical control, adaptive conversion, and evacuation of the transformer 110.

[0086] In summary, the system in this embodiment is mainly applicable to the technical improvement and energy efficiency control of the vacuum system used in the vacuum evacuation process of various transformers 110. This technology is based on the corresponding change characteristics of the pumping speed and vacuum degree when the vacuum system is working, combined with the three-stage or multi-stage vacuum matching structure of the existing large transformer 110 evacuation system to meet the requirements of large pumping speed and high vacuum. By adding a pumping speed measuring device 9 to the vacuum system and adding a bypass structure to the rear-stage Roots vacuum pump (i.e., the Roots pump), the vacuum system can perform the step-by-step switching of the large pumping speed vacuum pump 2 according to the real-time measured pumping speed, the effective pumping speed of each stage of the vacuum pump 2, and the vacuum degree requirements during operation, reducing the unnecessary investment of the rear-stage Roots vacuum pump (i.e., the Roots pump) in the full vacuum working state in the later stage, reducing the energy consumption and equipment loss during the long-term evacuation process.

[0087] This system solves the unnecessary situation where the original high-power second-stage Roots pump 3 always works in the case of high vacuum and low pumping speed, effectively reduces the working time of the second-stage Roots pump 3, extends its service life, saves unnecessary energy consumption, and reduces the evacuation cost.

[0088] Embodiment 2

[0089] In this embodiment, taking the transformer 110 scenario as an example, the overall working process of the hierarchical control vacuum system in Embodiment 1 is described as follows:

[0090] As Figure 1 shown, after the transformer 110 is assembled and sealed, it is necessary to connect the vacuum system to the upper evacuation nozzle of the transformer 110 through a hose for vacuum degassing and dehydration treatment. According to the different structures and types of the transformer 110, the vacuum system evacuation control is as follows:

[0091] According to the hierarchical control requirements, the pumping speed, vacuum degree, evacuation time, etc. corresponding to the switching of each stage of the vacuum pump 2 during the evacuation process are set separately on the control cabinet.

[0092] First, when electrified, the first branch valve 41, the second branch valve 42, and the first main passage valve 6 are normally open, and the second control valve 5 is normally closed. Open the pipeline valves connected to the transition tank 10 and the transformer 110 (i.e., the second main passage valve 7) and other pipeline valves. After clicking start, the first vacuum pump 21, the second vacuum pump 22, the primary roots pump 31, and the secondary roots pump 32 are sequentially started according to the vacuum degrees corresponding to the preset levels of the vacuum pumps 2, and the transformer 110 is evacuated.

[0093] Here, examples of the permitted start vacuum degree values corresponding to the levels of the vacuum pumps 2 are given: The first permitted start value (vacuum pump 2): atmospheric pressure; the second permitted start value (primary roots pump 31): 5000 Pa; the third permitted start value (secondary roots pump 32, which may include the second-stage roots pump 3, the third-stage roots pump 3, and even multi-stage roots pumps 3): 1000 Pa. That is to say, the vacuum pump 2 can be started at atmospheric pressure; when the vacuum degree in the system (evacuation pipeline 1) drops to 5000 Pa, the primary roots pump 31 starts and cooperates with the vacuum pump 2 for evacuation; when the vacuum degree in the system drops to 1000 Pa, the secondary roots pump 32 starts and cooperates with the vacuum pump 2 and the primary roots pump 31 for evacuation to meet the vacuum degree requirements for oil replenishment.

[0094] During the evacuation process, the pumping speed detection device and the vacuum gauge 8 detect the pumping speed and vacuum degree of the system in real time. When the pumping speed rapidly changes from low to high and then from high to low and gradually decreases, the vacuum degree will also continuously change from large to small. When the pumping speed measuring device 9 detects that the pumping speed of the system is lower than a certain value of the effective pumping speed of the primary roots pump 31, the bypass valve of the secondary roots pump 32 (i.e., the second control valve 5) is automatically opened, then the secondary roots pump 32 and the first main passage valve 6 at the front end are closed. At the same time, the first vacuum pump 21 and the second vacuum pump 22 automatically stop the first vacuum pump 21 or the second vacuum pump 22 in combination with the preset economic matching relationship with the primary roots pump 31, and synchronously close the first branch valve 41 or the second branch valve 42 at the inlet end of the corresponding vacuum pump 2, and continue to evacuate the transformer 110 to the corresponding vacuum degree and maintain for a specified time before proceeding to the next process. Thus, during the subsequent high vacuum and maintenance time, the secondary roots pump 32 with the highest power and value in the vacuum system is cut out of the working state, achieving the purpose of energy conservation and extended service life.

[0095] Secondly, the large pumping speed vacuum system used in existing large transformers 110 is mainly used for evacuating the large space inside the transformer body of the transformer 110. In the vacuum oil filling link after the transformer 110 is filled with oil to the top of the tank, the maximum pumping speed is not required at all to meet the evacuation requirements. Therefore, when using this equipment for this purpose, only need to switch the program to the vacuum oil filling mode, automatically close the valves at the inlet ends of the first vacuum pump 21 or the second vacuum pump 22 (which can be set in advance correspondingly), open the bypass valve of the secondary roots pump 32 (i.e., the second control valve 5), close the first main passage valve 6, and after the motor starts, a vacuum system with only one vacuum pump 2 and the first-stage roots pump 31 running can be realized, which can not only meet the needs of vacuum oil filling, but also achieve energy consumption savings and loss reduction when the secondary roots pump 32 is not working, and effectively extend the service life of the core vacuum pump 2.

[0096] From multiple aspects such as technology, quality, cost, and advancement in the manufacturing process of the transformer 110, in view of the actual situation that all vacuum pumps 2 in the vacuum system are always running during the long process of evacuating the transformer 110 from atmospheric pressure to high vacuum by the existing transformer 110 vacuum pumping unit, through the test and analysis research on the working characteristics, pumping speed, and variable pressure data and curves of the vacuum pumps 2, the present invention embodiment proposes a brand-new structural scheme and control method.

[0097] Moreover, this technical solution effectively avoids the unnecessary waste in the long-term operation process of the existing transformer 110 vacuum system, and effectively increases the service life of the high-value core vacuum pump 2.

[0098] Therefore, this technology has high technical value, economic value, application value, and promotion value.

[0099] Embodiment 3

[0100] The embodiment of the present invention also discloses a transformer oil filling system, including: an oil filling device and the hierarchical control vacuum system in Embodiment 1.

[0101] Among them, the controller of the hierarchical control vacuum system is electrically connected to the oil filling device, and is used to control some of the roots pumps 3 and some of the vacuum pumps 2 to close when the pumping speed data is less than or equal to the preset pumping speed threshold, maintain at least one vacuum pump 2 and at least one roots pump 3 for long-term evacuation, and send a start signal to the oil filling device. The oil filling device is used to fill the transformer 110 according to the start signal.

[0102] Specifically, the large pumping speed vacuum system used in the existing large transformer 110 is mainly used for evacuating the large space inside the transformer body. In the vacuum oil filling link after the transformer 110 is filled with oil to the tank top, the maximum pumping speed is not required at all to meet the evacuation requirements. Therefore, when using this equipment for this purpose, only the program needs to be switched to the vacuum oil filling mode, the valves at the inlet ends of the first vacuum pump 21 or the second vacuum pump 22 are automatically closed (correspondence can be set in advance), the bypass valve of the secondary Roots pump 32 (i.e., the second control valve 5) is opened, the first main passage valve 6 is closed, and after the motor starts, a vacuum system with only one vacuum pump 2 and the primary Roots pump 31 running is realized, which can not only meet the need of vacuum oil filling, but also save energy consumption and reduce losses when the secondary Roots pump 32 is not working, and effectively extend the service life of the core vacuum pump 2.

[0103] Embodiment 4

[0104] In the embodiment of the present invention, a method for evacuating a transformer is also disclosed. Using the hierarchical control vacuum system in Embodiment 1, the method includes:

[0105] Evacuate the transformer 110 through the vacuum pump 2 and the Roots pump 3.

[0106] Measure the pumping speed in the evacuation pipeline 1 to obtain pumping speed data.

[0107] When the pumping speed data is less than or equal to the preset pumping speed threshold, control some of the Roots pumps 3 and some of the vacuum pumps 2 to close, and maintain at least one vacuum pump 2 and at least one Roots pump 3 for long-term evacuation.

[0108] In some embodiments, evacuating the transformer 110 through the vacuum pump 2 and the Roots pump 3 includes: obtaining the pumping speed data and the vacuum degree permission start value in the evacuation pipeline 1,

[0109] The vacuum degree permission start value includes: the first permission start value, the second permission start value, and the third permission start value. The first permission start value, the second permission start value, and the third permission start value decrease in sequence.

[0110] When the vacuum degree data is less than or equal to the first permission start value, start the vacuum pump 2 and evacuate through the vacuum pump 2.

[0111] When the vacuum degree data is less than or equal to the second permission start value, start the primary Roots pump 31 in the Roots pump 3, and evacuate through the vacuum pump 2 and the primary Roots pump 31 together.

[0112] When the vacuum degree data is less than or equal to the third permission start value, start the secondary Roots pump 32 in the Roots pump 3, and evacuate through the vacuum pump 2, the primary Roots pump 31, and the secondary Roots pump 32 together.

[0113] Exemplarily, the first permission start value (vacuum pump 2): atmospheric pressure; the second permission start value (primary Roots pump 31): 5000 Pa; the third permission start value (secondary Roots pump 32, which may include a second-stage Roots pump 3, a third-stage Roots pump 3, or even a multi-stage Roots pump 3): 1000 Pa.

[0114] In some embodiments, when the pumping speed data is less than or equal to a preset pumping speed threshold, the control unit shuts down some of the Roots pumps 3 and some of the vacuum pumps 2, and maintains at least one vacuum pump 2 and at least one Roots pump 3 for long-term evacuation. Specifically:

[0115] When the pumping speed data is less than or equal to a preset pumping speed threshold, maintain one of the vacuum pumps 2 in operation, and shut down the remaining vacuum pumps 2, and, maintain the primary Roots pump 31 in operation, and shut down all the secondary Roots pumps 32.

[0116] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the embodiments of the present invention, and these modifications and improvements are also regarded as the protection scope of the embodiments of the present invention.

Claims

1. A hierarchical control vacuum system, characterized in that, Comprising: A vacuum pipeline (1), a vacuum pump (2), a Roots pump (3), a pumping speed measuring device (9) and a controller; The vacuum pipeline (1) is communicated with a transformer (110); The number of the vacuum pumps (2) is two or more, and the vacuum pumps (2) are communicated with the vacuum pipeline (1); The number of the Roots pumps (3) is two or more, the Roots pumps (3) are located between the vacuum pumps (2) and the transformer (110) and are communicated with the vacuum pipeline (1), and the vacuum pumps (2) and the Roots pumps (3) cooperate to evacuate the transformer (110); The pumping speed measuring device (9) is communicated with the vacuum pipeline (1) and is used for measuring the pumping speed in the vacuum pipeline (1); The controller is electrically connected to the pumping speed measuring device (9) and the Roots pumps (3) respectively, and is used for receiving the pumping speed data sent by the pumping speed measuring device (9), and when the pumping speed data is less than or equal to a preset pumping speed threshold, controlling some of the Roots pumps (3) and some of the vacuum pumps (2) to be closed, and maintaining at least one vacuum pump (2) and at least one Roots pump (3) for long-term evacuation.

2. The hierarchical control vacuum system according to claim 1, wherein The vacuum pipeline (1) is provided with a main passage (11) and a plurality of evacuation branches (12), the number of the evacuation branches (12) is plural, the plurality of evacuation branches (12) are connected in parallel with each other and are all communicated with the main passage (11); The number of the evacuation branches (12) is the same as the number of the vacuum pumps (2), and one vacuum pump (2) is arranged on each parallel branch.

3. The hierarchical control vacuum system according to claim 2, characterized in that, The vacuum pipeline (1) further includes first control valves (4), the number of the first control valves (4) is the same as the number of the evacuation branches (12), one first control valve (4) is arranged on each evacuation branch (12), and the first control valve (4) is communicated with the gas inlet end of the vacuum pump; The controller is electrically connected to the first control valves (4) and is used for controlling some of the vacuum pumps (2) to be closed and controlling the corresponding first control valves (4) to be closed when the pumping speed data is less than or equal to a preset pumping speed threshold, so as to cut off the corresponding evacuation branches (12).

4. The hierarchical control vacuum system according to claim 2, wherein Two or more of the Roots pumps (3) are all connected in series on the main passage (11).

5. The hierarchical control vacuum system according to claim 4, characterized in that, The Roots pump (3) includes a primary Roots pump (31) and a secondary Roots pump (32), the number of the primary Roots pumps (31) is one, and the number of the secondary Roots pumps (32) is at least one; The vacuum pipeline (1) further includes bypass branches (13), the number of the bypass branches (13) is equal to the number of the secondary Roots pumps (32), and each bypass branch (13) is connected in parallel with a secondary Roots pump (32), and two ends of the bypass branch (13) are respectively communicated with the inlet end and the outlet end of the secondary Roots pump (32); A second control valve (5) is arranged on each bypass branch (13).

6. The hierarchical control vacuum system according to claim 5, characterized in that, The controller is also electrically connected to the second control valve (5) and is configured to control the opening of the second control valve (5) when the pumping speed data is less than or equal to a preset pumping speed threshold, so that the corresponding bypass branch (13) is conducted.

7. The hierarchical control vacuum system according to claim 5, wherein The hierarchical control vacuum system further includes a vacuum probe, which is communicated with the evacuation pipeline (1), and the vacuum probe is used to measure the vacuum degree in the evacuation pipeline (1). The controller is electrically connected to the vacuum probe and is configured to receive the vacuum degree data sent by the vacuum probe. The controller is further configured to control the start of each vacuum pump (2) and each Roots pump (3) according to the vacuum degree data and a preset permitted start value of the vacuum degree.

8. The hierarchical control vacuum system according to any one of claims 1 to 7, characterized in that, The hierarchical control vacuum system further includes a transition tank (10), which is located between the evacuation pipeline (1) and the transformer (110), and the evacuation pipeline (1) is communicated with the transformer (110) through the transition tank (10).

9. A transformer oil replenishment system, characterized in that, Comprising: an oil replenishing device and the hierarchical control vacuum system according to any one of claims 1 to 8. The controller of the hierarchical control vacuum system is electrically connected to the oil replenishing device and is configured to control the shutdown of some Roots pumps (3) and some vacuum pumps (2) when the pumping speed data is less than or equal to a preset pumping speed threshold, maintain at least one vacuum pump (2) and at least one Roots pump (3) for long-time evacuation, and send a start signal to the oil replenishing device. The oil replenishing device is configured to replenish oil to the transformer (110) according to the start signal.

10. A method for evacuating a transformer, characterized in that, Using the hierarchical control vacuum system according to any one of claims 1 to 8, the method includes: evacuating the transformer (110) through the vacuum pump (2) and the Roots pump (3). measuring the pumping speed in the evacuation pipeline (1) to obtain pumping speed data. When the pumping speed data is less than or equal to a preset pumping speed threshold, control the shutdown of some Roots pumps (3) and some vacuum pumps (2), and maintain at least one vacuum pump (2) and at least one Roots pump (3) for long-time evacuation.

11. The method according to claim 10, characterized in that, The evacuating the transformer (110) through the vacuum pump (2) and the Roots pump (3) includes: obtaining the pumping speed data and the permitted start value of the vacuum degree in the evacuation pipeline (1). The permitted start value of the vacuum degree includes: a first permitted start value, a second permitted start value, and a third permitted start value, and the first permitted start value, the second permitted start value, and the third permitted start value decrease in sequence. When the vacuum degree data is less than or equal to the first permitted start value, start the vacuum pump (2) and evacuate through the vacuum pump (2). When the vacuum degree data is less than or equal to the second permitted start value, start the first-stage Roots pump (31) in the Roots pump (3) and evacuate jointly through the vacuum pump (2) and the first-stage Roots pump (31). When the vacuum degree data is less than or equal to the third permitted start value, start the secondary Roots pump (32) in the Roots pump (3) and evacuate jointly through the vacuum pump (2), the first-stage Roots pump (31), and the secondary Roots pump (32).

12. The method according to claim 11, wherein When the pumping speed data is less than or equal to a preset pumping speed threshold, the control part shuts down some roots pumps (3) and some vacuum pumps (2), and maintains at least one vacuum pump (2) and at least one roots pump (3) for long-time evacuation. Specifically: When the pumping speed data is less than or equal to a preset pumping speed threshold, maintain one of the vacuum pumps (2) in operation, and shut down the remaining vacuum pumps (2). Also, maintain the primary roots pump (31) in operation, and shut down all secondary roots pumps (32).

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