Hot air circulation drying method and system for transformer core

Abstract

The application discloses a hot air circulation drying method and system for a transformer core, and comprises a hot air circulation stage and a high vacuum stage. The hot air circulation stage is divided into a first hot air circulation stage, a second hot air circulation stage and a third hot air circulation stage according to the temperature of the core. According to the application, the hot air circulation stage is divided into three stages according to the different moisture contents of the core in different temperature stages. The hot air duration and the pressure reduction duration of the three stages are adjusted according to the different moisture contents of the core in different time periods, so that rusting of the core during the drying process can be avoided, the drying time can be shortened, and the drying efficiency can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of transformer processing, in particular to a hot air circulation drying method and system for transformer core. BACKGROUND

[0002] During the hot air circulation drying process of the transformer core, the core is prone to rusting. Once the core rusts, it will affect the partial discharge of the transformer, thereby affecting the service life of the transformer. The traditional transformer core is dried by multiple rounds of hot air circulation. The traditional hot air circulation drying is to place the transformer in a heated drying tank, and then circulate hot air through a fan. After a period of hot air circulation, the pressure is reduced through a vacuum pumping system to remove moisture in the air, and then air is introduced. Repeat the above process to dry the core.

[0003] The disadvantage of the traditional hot air circulation drying is that the duration and control conditions of each round of hot air circulation are exactly the same, and there is no optimization according to the different moisture content of the core at different times. The core dried by this method often rusts in large areas. The main reason for rusting is that the core and the insulating material release water during the heating process, generating a large amount of saturated steam attached to the surface of the core, which generates chemical reactions to form rust. And this method takes a long time to dry. The drying time of a 35KV transformer is more than 30 hours. SUMMARY

[0004] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application provides a hot air circulation drying method and system for transformer core, which can dry the core, avoid rusting of the core, and reduce the drying time.

[0005] According to the hot air circulation drying method for transformer core according to the first aspect of the present application, the transformer core is placed in a drying tank, hot air is provided to the drying tank through a hot air circulation system, and the pressure of the drying tank is reduced through a vacuum pumping system. The hot air circulation drying method includes a hot air circulation stage and a high vacuum stage. The hot air circulation stage includes the following steps

[0006] First hot air circulation stage: set the initial space temperature and the maximum space temperature, and start multiple rounds of hot air circulation drying at the initial space temperature. The steps of the hot air circulation drying are

[0007] According to the current space temperature, the hot air is circulated.

[0008] Stop the hot air circulation, and reduce the pressure through the vacuum pumping system.

[0009] Stop the pressure reduction, and introduce dry air into the drying tank.

[0010] The temperature of the space in each hot air circulation drying cycle is increased by T1 degrees until the maximum space temperature is reached.

[0011] The temperature of the transformer core is monitored during the first hot air circulation stage, and if it reaches 55 degrees, the second hot air circulation stage is entered.

[0012] The second hot air circulation stage: multiple rounds of hot air circulation drying are continued at the maximum space temperature, the pressure reduction duration of the hot air circulation drying in the second hot air circulation stage is less than that in the first hot air circulation stage, and the hot air circulation duration of the hot air circulation drying in the second hot air circulation stage is greater than that in the first hot air circulation stage.

[0013] The temperature of the transformer core is monitored during the second hot air circulation stage, and if it reaches 75 degrees, the third hot air circulation stage is entered.

[0014] The third hot air circulation stage: multiple rounds of hot air circulation drying are continued at the maximum space temperature, the pressure reduction duration of the hot air circulation drying in the third hot air circulation stage is less than that in the second hot air circulation stage, and the hot air circulation duration of the hot air circulation drying in the third hot air circulation stage is greater than that in the second hot air circulation stage.

[0015] The temperature of the transformer core is monitored during the third hot air circulation stage, and if it reaches 90 degrees, the high vacuum stage is entered.

[0016] The high vacuum stage: heating and pressure reduction of the transformer core are continued until the temperature of the transformer core, the vacuum degree in the drying tank, and the dryness all reach the specified values.

[0017] The hot air circulation drying method for the transformer core according to the first aspect of the present application has at least the following beneficial effects:

[0018] The embodiment of the present application divides the hot air circulation stage into three stages according to the temperature of the transformer core. The first hot air circulation stage is performed before the temperature of the transformer core reaches 55 degrees, at which time the water content in the core and the insulation material is the highest. Each round of hot air circulation drying increases the space temperature by T1 degrees. The temperature in the drying tank is gradually increased through multiple temperature increases, so as to avoid the formation of an absolutely dry layer in the insulation material due to too rapid temperature increase. After each temperature increase, the water vapor in the drying tank is extracted through pressure reduction, so as to avoid the reaction between the water vapor and the core and effectively prevent the core from rusting. The hot air circulation duration in the first hot air circulation stage is the shortest, and the pressure reduction duration is the longest, so that the water vapor in the drying tank can be extracted in time and to the maximum extent, thereby avoiding the reaction between the water vapor and the core and effectively preventing the core from rusting. The second hot air circulation stage is performed when the temperature of the core is between 55 degrees and 75 degrees. At this time, the water content in the core and the insulation material is reduced, so that the second hot air circulation stage continues multiple rounds of hot air circulation drying at the highest space temperature. The hot air circulation duration in the second hot air circulation stage is increased, and the pressure reduction duration is reduced, so that the temperature increase speed of the core is accelerated, the drying time is shortened, and the drying efficiency is improved. The third hot air circulation stage is performed when the temperature of the core is between 75 degrees and 90 degrees. At this time, the water content in the core and the insulation material is very low, so that the hot air circulation duration is further increased, and the pressure reduction duration is further shortened, so that the temperature increase speed of the core is further accelerated, and the drying time is further shortened. Finally, the high-vacuum stage is entered to continue heating and pressure reduction of the core until the temperature of the transformer core, the vacuum degree in the drying tank, and the dryness degree all reach specified values.

[0019] According to the present application, the hot air circulation stage is divided into three stages according to the water content at different temperature stages of the core. The hot air duration and the pressure reduction duration in the three stages are adjusted according to the water content at different time periods of the core, so that the core can be prevented from rusting during the drying process, and the drying time can be shortened and the drying efficiency can be improved.

[0020] According to some embodiments of the present application, in the first hot air circulation stage, if the space temperature has not reached the highest space temperature when the temperature of the transformer core reaches 55 degrees, the current space temperature is directly increased to the highest space temperature immediately, and the second hot air circulation stage is entered after the current round of hot air circulation drying is completed.

[0021] According to some embodiments of the present application, the first hot air circulation stage includes five rounds of hot air circulation drying.

[0022] According to some embodiments of the present application, in the five rounds of hot air circulation drying, the pressure reduction duration in the first round of hot air circulation drying is greater than the pressure reduction duration in the other four rounds.

[0023] According to some embodiments of the present application, the stop condition for ending pressure reduction in the hot air circulation drying is that the pressure reduction duration is reached or the vacuum degree in the drying tank reaches a limited value.

[0024] According to some embodiments of the present application, the initial space temperature is 80-100 degrees, and the maximum space temperature is 130-135 degrees.

[0025] According to some embodiments of the present application, the stop condition for supplying drying air into the drying tank in the hot air circulation drying is that the pressure inside and outside the drying tank is the same.

[0026] The hot air circulation drying system for a transformer core according to the second aspect of the embodiments of the present application comprises: a drying tank for placing a transformer; a hot air circulation system for supplying hot air into the drying tank; a vacuum pumping system connected to the drying tank for reducing the pressure in the drying tank; and a breaking vacuum system connected to the drying tank for supplying drying air.

[0027] The hot air circulation drying system for a transformer core according to the second aspect of the embodiments of the present application has at least the following beneficial effects:

[0028] The embodiments of the present application divide the hot air circulation stage into three stages according to the temperature of the transformer core. When the temperature of the core reaches 55 degrees, the first hot air circulation stage is performed, at which time the water content in the core and the insulation material is the highest. Each round of hot air circulation drying increases the space temperature by T1 degrees. The temperature in the drying tank is gradually increased through multiple temperature increases, so as to avoid the formation of a dry layer in the insulation material due to rapid temperature increase. After each temperature increase, the water vapor in the tank is extracted through pressure reduction, so as to avoid rusting of the core and improve the insulation effect of drying. In the first hot air circulation stage, the hot air circulation duration of the hot air circulation drying is the shortest, and the pressure reduction duration is the longest. The water vapor in the drying tank can be extracted in time and to the maximum extent, so as to avoid the reaction of the water vapor and the core and effectively prevent the core from rusting. When the temperature of the core is between 55 degrees and 75 degrees, the second hot air circulation stage is performed. At this time, the water content in the core and the insulation material is reduced. Therefore, the second hot air circulation stage continues multiple rounds of hot air circulation drying at the highest space temperature. In the second hot air circulation stage, the hot air circulation duration is increased, and the pressure reduction duration is reduced. The temperature increase speed of the core can be accelerated, the drying time can be shortened, and the drying efficiency can be improved. When the temperature of the core is between 75 degrees and 90 degrees, the third hot air circulation stage is performed. At this time, the water content in the core and the insulation material is very low. Therefore, the hot air circulation duration is further increased, the pressure reduction duration is further shortened, the temperature increase speed of the core is further accelerated, and the drying time is further shortened. Finally, the high vacuum stage is entered to continue heating and pressure reduction of the core until the temperature of the transformer core, the vacuum degree in the drying tank, and the drying degree all reach specified values.

[0029] The application divides the hot air circulation stage into three stages according to the different moisture contents of the iron core in different temperature stages, and adjusts the hot air duration and pressure reduction duration of the three stages according to the different moisture contents of the iron core in different time periods, so that rusting of the iron core in the drying process can be avoided, and the drying time can be shortened and the drying efficiency can be improved.

[0030] According to some embodiments of the application, the vacuum system further comprises a dew point sensor for detecting the moisture content of the extracted air in the drying tank.

[0031] According to some embodiments of the application, a controller is further included, which is connected to the control ends of the drying tank, the hot air circulation system, the vacuum system and the air breaking system respectively.

[0032] Additional aspects and advantages of the application will be described in the following description and will be apparent from the following description and the organization of the application. BRIEF DESCRIPTION OF DRAWINGS

[0033] The application will be further described below in conjunction with the drawings and embodiments, in which:

[0034] Figure 1 The flow chart of the hot air circulation drying method for the transformer iron core in the embodiments of the application. DETAILED DESCRIPTION

[0035] The embodiments of the application will be described in detail below, examples of which are shown in the drawings, in which the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application.

[0036] In the description of the application, it should be understood that the orientation description, such as the up, down, etc. orientation or position relationship is based on the orientation or position relationship shown in the drawings, and is only for the convenience of describing the application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the application.

[0037] In the description of the application, the plural refers to two or more. If there is a description of the first, second, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0038] In the description of the present application, unless otherwise explicitly defined, the words such as arrangement, installation, connection and the like should be understood broadly, and the person skilled in the art can determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0039] Referring to Figure 1 As shown in the figure, a hot air circulation drying method of a transformer core, the transformer core is placed in a drying tank, hot air is provided in the drying tank through a hot air circulation system, the drying tank is depressurized through a vacuum pumping system, including a hot air circulation stage and a high vacuum stage, the hot air circulation stage is divided into three stages according to the core temperature, as follows:

[0040] S100, first hot air circulation stage: set initial space temperature and maximum space temperature, start multiple rounds of hot air circulation drying at the initial space temperature, the space temperature of each round of hot air circulation drying is increased by T1 degrees until the maximum space temperature is reached; the temperature of the transformer core is monitored in the first hot air circulation stage, and if it reaches 55 degrees, it enters the second hot air circulation stage;

[0041] Specifically, in the present embodiment, the initial space temperature is set to 80-100 degrees, the maximum space temperature is 130-135 degrees, and T1 is calculated according to the difference between the round, the initial space temperature and the maximum space temperature. For example, if a total of five rounds of hot air circulation drying are performed, and the space temperature is set to 80 degrees, and the maximum space temperature is 130 degrees, then each time the temperature is increased by 12.5 degrees.

[0042] It should be noted that the specific steps of hot air circulation drying are as follows:

[0043] S101, hot air circulation according to the current space temperature;

[0044] It should be noted that the drying tank is configured with a heating pipe and an in-tank temperature sensor, and the heating pipe is filled with heat conducting oil. Hot air circulation according to the current space temperature means that the temperature in the drying tank is first raised to 80-100 degrees by heating the heat conducting oil, and then the fan of the hot air circulation system is started to form a hot air circulation in the tank.

[0045] S102, stop hot air circulation and depressurize through the vacuum pumping system;

[0046] It should be noted that the fan is turned off to stop hot air circulation when the preset hot air circulation duration is reached, and the hot air circulation duration is different in different stages, at this time the temperature of the transformer rises, releasing water vapor in the core and insulating material, therefore the drying tank needs to be depressurized by the vacuum pumping system, i.e. the air containing water vapor in the drying tank is pumped out.

[0047] S103, stop depressurizing and introduce dry air into the drying tank.

[0048] It should be noted that the stop condition for ending the pressure reduction is that the pressure reduction duration is reached or the vacuum degree in the drying tank reaches a limited value, that is, time or vacuum degree can be used as the stop condition, and the pressure reduction duration is mainly used as the stop condition. After the vacuum system is closed and the pressure reduction is stopped, dry air is introduced into the drying tank to make the pressure in the drying tank and outside the drying tank the same.

[0049] It should be noted that the transformer core is provided with a core temperature sensor, so that the real-time temperature of the core can be obtained. If the temperature of the transformer core reaches 55 degrees and the space temperature has not reached the highest space temperature in step S100, the current space temperature is directly raised to the highest space temperature immediately and enters the second hot air circulation stage after the end of the current hot air circulation drying. If the core temperature reaches 55 degrees after reaching the highest space temperature, the hot air circulation drying is continued with the highest space temperature, the control parameters and the environmental conditions of the first stage until the core temperature reaches 55 degrees. This is because through many field tests, the water content in the core and the insulating material is the highest in the interval from room temperature to 55 degrees, so the temperature is raised step by step in the first hot air circulation stage, and the hot air circulation time is shortened and the pressure reduction is frequent. Water vapor can be removed in time and rust can be avoided.

[0050] In the first hot air circulation stage, five rounds of hot air circulation drying are set in the embodiment, and the pressure reduction duration of the first round of hot air circulation drying is longer than that of the other four rounds. This is because the water vapor content is the highest in the initial hot air circulation, so it is necessary to fully remove the water vapor, and therefore the initial pressure reduction duration is prolonged.

[0051] For example, the process of the first hot air circulation stage is described in detail below with five rounds of hot air circulation drying as an example.

[0052] The first round of hot air circulation drying: the space temperature is set to 80-120 degrees, the hot air circulation system is started to perform hot air circulation for 5-20 minutes, then the hot air circulation system is closed, the vacuum system is started to perform pressure reduction, and the pressure reduction duration is set to 60-240 minutes. After the time is up, the vacuum system is stopped, and dry air is introduced into the drying tank to break the vacuum.

[0053] The second round of hot air circulation drying: the space temperature is set to 100-120 degrees, the hot air circulation system is started to perform hot air circulation for 10-30 minutes, then the hot air circulation system is closed, the vacuum system is started to perform pressure reduction, and the pressure reduction duration is set to 30-60 minutes. After the time is up, the vacuum system is stopped, and dry air is introduced into the drying tank to break the vacuum.

[0054] Third hot air circulation drying: the space temperature is set to 110-125 degrees, the hot air circulation system is started for 10-30 minutes of hot air circulation, then the hot air circulation system is closed, the vacuum pumping system is started for pressure reduction, the pressure reduction duration is set to 30-60 minutes, and after the time is up, the vacuum pumping system is stopped, dry air is introduced into the drying tank to break the vacuum.

[0055] Fourth hot air circulation drying: the space temperature is set to 120-125 degrees, the hot air circulation system is started for 10-30 minutes of hot air circulation, then the hot air circulation system is closed, the vacuum pumping system is started for pressure reduction, the pressure reduction duration is set to 30-60 minutes, and after the time is up, the vacuum pumping system is stopped, dry air is introduced into the drying tank to break the vacuum.

[0056] Fifth hot air circulation drying: the space temperature is set to 125-135 degrees, the hot air circulation system is started for 10-30 minutes of hot air circulation, then the hot air circulation system is closed, the vacuum pumping system is started for pressure reduction, the pressure reduction duration is set to 30-60 minutes, and after the time is up, the vacuum pumping system is stopped, dry air is introduced into the drying tank to break the vacuum.

[0057] S200, second hot air circulation stage: continue to perform multiple rounds of hot air circulation drying at the highest space temperature, the pressure reduction duration of the hot air circulation drying in the second hot air circulation stage is less than the pressure reduction duration of the hot air circulation drying in the first hot air circulation stage, and the hot air circulation duration of the hot air circulation drying in the second hot air circulation stage is greater than the hot air circulation duration of the hot air circulation drying in the first hot air circulation stage;

[0058] In the second hot air circulation stage, the temperature of the transformer core is monitored, and if it reaches 75 degrees, the third hot air circulation stage is entered;

[0059] It should be noted that the second hot air circulation stage refers to the drying stage in which the temperature of the core is in the range of 55-75 degrees. In this stage, the water vapor in the core and the insulation material is reduced, so the hot air circulation time is increased, the pressure reduction duration and frequency are reduced, the drying efficiency is improved, and the core is not rusted.

[0060] For example, in the second hot air circulation stage, the hot air circulation duration is set to 30-90 minutes, the pressure reduction duration is set to 20-30 minutes, and the vacuum degree at the end of the pressure reduction in the second hot air circulation stage can also be set lower to further reduce the risk of rusting of the core.

[0061] S300, third hot air circulation stage: continue to carry out multi-round hot air circulation drying at the highest space temperature, the pressure reduction duration of the hot air circulation drying in the third hot air circulation stage is less than the pressure reduction duration of the hot air circulation drying in the second hot air circulation stage, and the hot air circulation duration of the hot air circulation drying in the third hot air circulation stage is greater than the hot air circulation duration of the hot air circulation drying in the second hot air circulation stage;

[0062] The temperature of the transformer core is monitored in the third hot air circulation stage, and if it reaches 90 degrees, the high vacuum stage is entered;

[0063] It should be noted that the third hot air circulation stage refers to the drying stage in which the core temperature is in the range of 75-90 degrees. At this stage, the transformer has very little water content, and the core is basically not rusted, so the pressure reduction duration is set to be the shortest, and the hot air circulation duration is set to be the longest. This is to allow the product to release moisture more easily, and to allow the hot air circulation time to be longer, so that the core temperature rises faster and the drying time is shortened.

[0064] For example, in the third hot air circulation stage, the hot air circulation duration is set to 60-120 minutes, and the pressure reduction duration is set to 10-20 minutes.

[0065] S400, high vacuum stage: continue to heat and reduce the pressure of the transformer core until the temperature of the transformer core, the vacuum degree and the dryness in the drying tank all reach the specified values.

[0066] It should be noted that the heating in the high vacuum stage is indirect heating by heat conducting oil. The air in the high vacuum stage tank is too little to allow hot air circulation heating, so the hot air circulation fan is not allowed to start. Therefore, there is no air breaking step in the high vacuum stage, but the transformer core is continuously heated and the tank is continuously reduced in pressure by the vacuum pumping system. The core temperature rises very little, about a few degrees. When the temperature of the transformer core reaches the final set value, and the vacuum degree and dryness in the drying tank reach the final set value, it is considered that the drying of the transformer core is complete. The vacuum degree in the drying tank is obtained by the air pressure sensor in the tank, and the dryness in the drying tank is obtained by the dew point sensor in the vacuum pumping system. The dew point sensor measures the water content in the air pumped out, thereby indirectly determining the dryness in the drying tank.

[0067] The application also relates to a hot air circulation drying system for a transformer core, which comprises a drying tank, a hot air circulation system, a vacuum pumping system and a vacuum breaking system. The drying tank is used for placing the transformer, the hot air circulation system is used for providing hot air into the drying tank, the vacuum pumping system is connected to the drying tank for reducing the pressure in the drying tank, and the vacuum breaking system is connected to the drying tank for providing dry air. The vacuum pumping system further comprises a dew point sensor for detecting the water content of the air pumped out of the drying tank. A controller is further included, which is connected to the control ends of the drying tank, the hot air circulation system, the vacuum pumping system and the vacuum breaking system respectively.

[0068] The application divides the hot air circulation stage into three stages according to the temperature of the transformer core. The first hot air circulation stage is performed when the temperature of the core reaches 55 DEG C, at which time the water content in the core and the insulation material is the highest. Each round of hot air circulation drying can increase the space temperature by T1 DEG C. The temperature in the drying tank is gradually increased through multiple temperature increases, so that the formation of the dry layer of the insulation material caused by the rapid temperature increase is avoided, and the water vapor in the drying tank is pumped out after each temperature increase, so that the rusting of the core is avoided and the insulation effect of the drying is improved. The hot air circulation duration of the hot air circulation drying in the first hot air circulation stage is the shortest, and the pressure reduction duration is the longest, so that the water vapor in the drying tank can be pumped out in time and to the maximum extent, the reaction between the water vapor and the core is avoided, and the rusting of the core is effectively prevented. The second hot air circulation stage is performed when the temperature of the core is between 55 DEG C and 75 DEG C, at which time the water content in the core and the insulation material is reduced. Therefore, the second hot air circulation stage continues multiple rounds of hot air circulation drying at the highest space temperature. The hot air circulation duration in the second hot air circulation stage is increased, and the pressure reduction duration is reduced, so that the temperature increasing speed of the core is accelerated, the drying time is shortened, and the drying efficiency is improved. The third hot air circulation stage is performed when the temperature of the core is between 75 DEG C and 90 DEG C, at which time the water content in the core and the insulation material is very low. Therefore, the hot air circulation duration is further increased, the pressure reduction duration is further shortened, the temperature increasing speed of the core is further accelerated, and the drying time is further shortened. Finally, the high vacuum stage is entered to continue heating and pressure reduction of the core until the temperature of the transformer core, the vacuum degree in the drying tank and the drying degree all reach the specified values.

[0069] The application divides the hot air circulation stage into three stages according to the water content in the core at different time periods. The hot air duration and the pressure reduction duration of the three stages are adjusted according to the water content in the core at different time periods, so that the rusting of the core in the drying process is avoided, and the drying time is shortened. The drying time of a 10KV transformer can be controlled within 15-20 hours, and the drying time of a 35KV transformer can be controlled within 18-30 hours. The drying efficiency is greatly improved, and the energy is saved.

[0070] The embodiments of the present application are described in detail above with reference to the drawings, but the present application is not limited to the above-described embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application.

Claims

1. A hot air circulation drying method of a transformer core, wherein a transformer core is placed in a drying tank, hot air is supplied to the drying tank by a hot air circulation system, and the drying tank is depressurized by a vacuum pumping system, characterized in that, The drying method comprises a hot air circulation stage and a high vacuum stage, and the hot air circulation stage comprises the following steps The first hot air circulation stage: setting an initial space temperature and a maximum space temperature, starting a plurality of rounds of hot air circulation drying at the initial space temperature, and the hot air circulation drying step is to perform hot air circulation according to the current space temperature; Stopping the hot air circulation, and performing pressure reduction through the vacuumizing system; Stopping the pressure reduction, and introducing dry air into the drying tank; The space temperature of each round of hot air circulation drying is increased by T1 degrees until the maximum space temperature is reached; In the first hot air circulation stage, the temperature of the transformer core is monitored, and if it reaches 55 degrees, the second hot air circulation stage is entered; The second hot air circulation stage: continuing to perform a plurality of rounds of hot air circulation drying at the maximum space temperature, the pressure reduction duration of the hot air circulation drying in the second hot air circulation stage is less than that in the first hot air circulation stage, and the hot air circulation duration of the hot air circulation drying in the second hot air circulation stage is greater than that in the first hot air circulation stage; In the second hot air circulation stage, the temperature of the transformer core is monitored, and if it reaches 75 degrees, the third hot air circulation stage is entered; The third hot air circulation stage: continuing to perform a plurality of rounds of hot air circulation drying at the maximum space temperature, the pressure reduction duration of the hot air circulation drying in the third hot air circulation stage is less than that in the second hot air circulation stage, and the hot air circulation duration of the hot air circulation drying in the third hot air circulation stage is greater than that in the second hot air circulation stage; In the third hot air circulation stage, the temperature of the transformer core is monitored, and if it reaches 90 degrees, the high vacuum stage is entered; The high vacuum stage: continuing to heat and reduce the pressure of the transformer core until the temperature of the transformer core, the vacuum degree in the drying tank and the drying degree all reach the specified values.

2. The hot air circulation drying method of a transformer core according to claim 1, characterized by, In the first hot air circulation stage, if the temperature of the transformer core reaches 55 degrees and the space temperature has not reached the maximum space temperature, the current space temperature is directly increased to the maximum space temperature immediately, and the second hot air circulation stage is entered after the end of the current round of hot air circulation drying.

3. The hot air circulation drying method of a transformer core according to claim 1, characterized by, The first hot air circulation stage comprises five rounds of hot air circulation drying.

4. The hot air circulation drying method of a transformer core according to claim 3, characterized by, In the five rounds of hot air circulation drying, the pressure reduction duration of the first round of hot air circulation drying is greater than that of the other four rounds.

5. The hot air circulation drying method of a transformer core according to claim 1, characterized by, The stop condition for ending the pressure reduction in the hot air circulation drying is that the pressure reduction duration is reached or the vacuum degree in the drying tank reaches a limited value.

6. The hot air circulation drying method of a transformer core according to claim 1, characterized by, The initial space temperature is 80-100 degrees, and the maximum space temperature is 130-135 degrees.

7. The hot air circulation drying method of a transformer core according to claim 1, characterized by, In the hot air circulation drying, the stop condition for introducing dry air into the drying tank is that the pressure inside and outside the drying tank is the same.

8. A hot air circulation drying system for a transformer core for carrying out the method according to any one of claims 1 to 7, characterized in that It comprises: A drying tank for placing a transformer; A hot air circulation system for providing hot air into the drying tank; A vacuumizing system connected to the drying tank for reducing the pressure of the drying tank; A breaking system connected to the drying tank for providing dry air.

9. The hot air circulation drying system of a transformer core according to claim 8, characterized by, The vacuumizing system further comprises a dew point sensor for detecting the water content of the extracted air in the drying tank.

10. The hot air circulation drying system of a transformer core according to claim 8, characterized by, The system further comprises a controller connected to the control terminals of the drying tank, the hot air circulating system, the vacuumizing system and the air breaking system respectively.

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