In June 2015, CET Technology installed a new KI-600 vacuum pressure impregnation system. Such equipment greatly enhances the quality of CET standard and custom electrical transformers and inductors. Varnish, a thermally-cured polymer resin, is used on transformers to protect the windings from environmental elements, such as moisture and other impurities. Varnish also helps reduce vibration of the windings, which reduces audible noise and extends the life of a transformer. There are basically two types of varnish process: dip and vacuum impregnation.
Varnish dip is a process where the transformers are dipped into a container containing the varnish, using a diluent to reduce the viscosity of the varnish and help it penetrate the windings.
Concentrated penetration enhances winding protection and vibration reduction. However, even with the solvent diluent, the penetration with a dip process is only somewhat successful. In some cases, transformer manufacturers pull a vacuum during the dip process (about 500Torr or 666 millibar) to improve penetration. Again, this step only is only somewhat successful, but it allows those manufacturers to claim they ‘vacuum varnish’. In reality, pulling a vacuum on a solvent-diluted varnish causes the solvent to evaporate, thus, the viscosity of the varnish increases over time.
Vacuum impregnation is the better varnish process.
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VPI entails placing the parts in a vacuum chamber while dry. Sometimes parts are heated to further drive off impurities. A vacuum is pulled down to about 1Torr (1.3millibar) and the vacuum chamber is filled with a solvent-less varnish. The vapor pressure of the solvent-less varnish is very low, so there is no evaporation or viscosity change. This allows better penetration of the varnish, the varnish is able to penetrate, often all the way into every layer of the windings as well as the bobbin and core–because the air has been removed from the chamber. Vacuum impregnation greatly increases the durability of the transformer, while significantly reducing audible noise.
Through this vacuum pressure impregnation, transformers and coils windings are evacuated at the vacuum phase in order to reduce the influence from moisture, air, and other impurities; at the pressure impregnation phase, varnish/resin will be pushed by pressure to coat the inside thoroughly, thus the whole insulation will be stronger, the insulation level and electric performance of coils and transformers will be improved. This breakthrough design operates by putting transformers into the VPI tank and using the vacuum to systematically pull out all moisture and air from the transformers. Moisture and air are easily evaporated in this process state. The residual water rate is less than 10 ppm with good insulation and humidity resistance. Other advantages include high dielectric properties, and a “green” option, which is to reuse the impregnating liquid to reduce environmental pollution.
This new system uses the advanced technology of vacuum, pressure vessel, pressurization, cooling, heating, and automatic control. This system can be equipped with PLC or a computer to offer full automatic measurements and control. The system also has a safety alarm and interlock protection device to guarantee safety. This highly effective Vacuum Pressure Impregnation system allows successful results in a shorter period of time, which leads to greater productivity and cost savings in the production of standard and custom transformers and inductors.