Vacuum Drying Process For 220KV Current Transformer

1. Scope of application
This process specification is applicable to vacuum drying of the 220 KV current transformer

2. Vacuum dring oven
Vacuum pump set, vacuum drying oven, heating and drying control system, trolley.

3. Preparation before vacuum drying
3.1 Vacuum autoclave cleaning and inspection
3.1.1 Before the new product is put into the vacuum drying autoclave, the inner surface of the vacuum drying autoclave must be cleaned, and the oil and dust on the inner surface of the drying autoclave shall be removed with alcohol
3.1.2 Check the sealing strips, valves and other devices in the drying autoclave, and replace them in time if there is any abnormality.
3.2 Inspection of vacuum pump system and heating and drying control system
3.2.1 Check the oil level of slide valve pump and booster pump in the vacuum pump set.

3.2.2 Open the vacuum pump set system, and check whether the trial operation meets the vacuum index requirements of the process, and timely repair if any abnormalities are found.
3.2.3 Check the temperature instrument and temperature sensor of the heating and drying control system, and set the parameters as the temperature required by the process.
3.2.4 Turn on the heating and drying control system, and timely repair if any abnormality is found in the trial operation.

3.3 Transformer into the autoclave
3.3.1 Check the quantity and number of vacuum drying products required, and fill in the vacuum drying operation record of oil-immersed transformer.
3.3.2 Care should be taken when entering the autoclave to avoid bump.
3.3.3 The distance between the autoclave body and the autoclave wall shall not be less than 200 mm. Contact between the autoclave body and the autoclave wall and the products shall be strictly prohibited.
3.3.4 Check the products, sealing ring, temperature sensor and cleaning inside the autoclave again, and confirm that there is no problem.

4. Operating rules
This operation is based on the experimental operation process record of RQTD-640 vacuum drying oven of the Hangzhou Ruiqin Mechanical Equipment Co., Ltd

4.1 Temperature setting: Set the temperature meter of the drying pipe at 110℃.

4.2 Body drying cycle hot air and vacuum drying process:
4.2.1 Heating: Open the heating valve and start the circulation of hot air.When the temperature reaches the thermocouple’s minimum temperature of 80°C, fully open the inlet and outlet valves of the autoclave and start recording every -hour.Raise the temperature of the autoclave to 110 ± 5℃(the highest point of the temperature measurement point is not higher than 120°C, and the lowest point is not lower than 100 °C), and maintain the temperature at this temperature for 40 hours(in case of rainy weather, the heating time is increased by 5 hours).
4.2.2 The first pumping: close the circulating hot air and exhaust valve, open the front vacuum pump, pump the vacuum slowly and uniformly at the pumping speed of not less than 1 hour, maintain the residual vacuum pressure below 350 Pa, control the autoclave temperature at 110 ± 5℃, maintain the pumping speed for 5 hours.
4.2.3 The second blast: close the vacuum valve and the vacuum pump, relieve the vacuum slowly for at least 5 min, open the circulating hot air and exhaust valve, blow the air for 24 hours, and maintain the autoclave temperature at 110 °C.
4.2.4 Second pumping: close the circulating hot air and exhaust valve, open the front vacuum pump, pump the vacuum slowly and uniformly at the pumping speed of not less than 1 hour, maintain the residual vacuum pressure below 350 Pa, control the autoclave temperature at 110 ± 5°C, maintain the pumping speed for 5 hours.
4.2.5 The third blast: close the vacuum valve and vacuum pump, relieve the vacuum slowly for at least 5 min, and open the circulation. Hot air and exhaust valve, blow air for 40 hours, and maintain the autoclave temperature at 110 ± 5°C.
4.2.6 The third time pumping: close the circulating hot air and exhaust valve, open the front vacuum pump, pump the vacuum slowly and uniformly at the pumping speed of not less than 1 hour, maintain the residual vacuum pressure below 350 Pa, control the autoclave temperature at 110 ± 5°C, maintain the pumping speed for 5 hours.
4.2.7 Improve the vacuum: start the booster pump to make the residual vacuum pressure below 50 Pa, keep the autoclave temperature under the state of 110 soil at 5°C for 45 hours, stop the gas supply, maintain the vacuum degree, and cool down naturally to 80°C.
4.2.8 Remove the vacuum: remove the vacuum for at least 5 min, open the autoclave cover, and lift the body out of the drying autoclave smoothly.

5. Precautions
If the operation is stopped under special circumstances such as power failure, the re-operation time should be guaranteed to be twice of the stopping time.

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