It is researched and developed as per the Pressure-Changed Drying Principle of German Doctor J. Moll, and combined with our company’s experience on design and manufacture of vacuum drying equipment. It is mainly used for drying the active parts of oil-immersed transformer, instrument transformer, capacitor and etc. It can decrease 30-45% drying time compared with traditional vacuum drying equipment. So it is a professional equipment with efficient energy saving and reliable performance.
　　It is National Torch Plan Project which is approved by Ministry of Science and Technology; it also won the Award for Advancement in Science and Technology of China and Award for Provincial Key New Product.

1、Advanced and reasonable heating principle
　　During heating transformers in pressure-changed vacuum drying equipment, the heating medium is moisture which is evaporated from transformers; heat will be exchanged between heater and transformer. This heating system is similar with vapor phase drying equipment; the heating is equal, efficient and stable.
　　2、High productivity
　　It only takes around 50 hours to finish drying 1pc transformer up to 110KV, 40000KVA; its productivity is almost same as vapor phase drying equipment.
　　3、 End point measuring
　　The end point of drying is measured as per the comparative method of Doctor J. Moll, which can be measured accurately and reliably at the end of drying by operating system.
　　4、Simple structure
　　Compared with hot air circulation drying equipment, there is no hot air circulation system in pressure-changed vacuum drying equipment; compared with vapor phase drying equipment, there are no systems related to kerosene in pressure-changed vacuum drying equipment. So its structure is very simple and convenient for operation and maintenance.
　　5、High automation
　　The drying process of this equipment can be controlled automatically because the drying process is clear and the control system is simple, and the auto-control system is reliable.
　　6、Low cost
　　Its price is only 2/3 of same size hot air circulation drying equipment, so this is high performance-price-ratio equipment.

Features

1. This technology is introduced from German Consult Gmbh company, which has scientific drying process.
　　2. The condenser is designed reasonable, made from stainless steel; useful life will be more than 20 years. Cooling chiller will provide cooling water (less than 20℃) for condenser, so that the moisture can be condensed maximum, in order to protect the vacuum pumps.
　　3. The pressure can be changed automatically as per transformer temperature during heating phase. The pressure in the autoclave can be decreased periodically to reasonable value, which can create the best condition for the moisture to be evaporated from the active part, in order to evaporate the moisture smoothly.
　　4. Compared with traditional vacuum drying equipment, our equipment can save energy more than 30%.
　　5. In the drying process for cores, rusty problem can be resolved efficiently, and even can drying up to the centre of core.
　　6. There are high vacuum meter and low vacuum meter for measuring vacuum degree so as to make sure the measurement can be accurate and reliable.
　　7. All the electrical components are purchased from Schneider German; control system is stable and reliable.
　　8. It is designed and manufactured as per the standard and norms of our country to make sure that it can be operated safely, and equipped with perfect interlock protection.
　　9. The door of big cuboid autoclave is sealed by double o-rings which sealing performance can be increased obviously.
　　10. The main parts of our equipment are designed as modules which finished the assembly and commissioning before delivery in order to decrease the workload at worksite maximum and increase the reliability and quality of assembly.

Drying process　　

　　Heating principle: take moisture which is evaporated from transformer as heating medium under vacuum and heat transfer by convection. There are 4 phases during drying process:
　　1. Preheat phase:
　　During this phase, there is low vacuum state in the autoclave, the moisture which is evaporated from the transformer will transfer the heat between heater and transformer in order to increase the heating efficiency and make the temperature equally. During this phase, the autoclave need to be evacuated discontinuously by vacuum pumps to suck out the moisture in order to make sure the moisture in the autoclave is under saturation state and prevent the moisture from condensing on the surface of transformer, after recirculated and repeated evacuation, the heat efficiency will be increased and the temperature will be equal in the autoclave, and the moisture in the deep insulation will be evaporated durative.
　　2. Pressure-changed & evaporation phase (Drying phase):
　　After preheat phase and the temperature of transformer has achieved the set value, then enter into pressure-changed & evaporation phase. During this phase: first evacuate the autoclave to suck out the moisture which is evaporated from the transformer; close the valve when the vacuum degree is increased enough, so that the residual moisture can keep transferring the heat between heater and transformer to increase the heat which had been lost because the moisture is vaporized from the insulation, then the moisture in the insulation will be evaporated out again, and the vacuum degree will be decreased, after a period of time, evacuate the autoclave again. Circulate and repeat this phase until the temperature of transformer is increased to the requirement of process, which is prepared for the final drying phase.
　　3. Final drying phase:
　　During pressure-changed & evaporation phase, the vacuum degree in the autoclave will be increased because most moisture are evaporated and evacuated. The process will enter into final drying phase when the vacuum degree achieved the set value of the process requirement. During final drying phase, keep evacuating the autoclave and suck out the residual moisture from the insulation till to end point measuring phase.
　　4. End point measuring
　　The main principle of end point measuring is: To measure the pressure-increasing-rate of moisture in autoclave, compares with the set value of process requirement to check the drying degree. The equipment will be shut off automatically after the end point measuring has been accepted, then the transformer can be taken out from autoclave.
　　Our company has already developed one special end point measuring instrument; we have already applied for patent and widely used this instrument on our equipments.

　　The schematic diagram

Standard structure：