There are dry and oil-filled capacitors base on filler materials property. Hereon we explain the popular filler materials on capacitors, such as silicon oil, vetatable oil like canola/castor Oil, solid epoxy resin, liquid epoxy resin, paraffin wax, nitrogen etc. We choose the filler materials on the strength of its characteristic like Insulation performance, thermal conductivity, the impact of its composition on the film, and the its stability under high temperature or electric field strength. Meanwhile, we consider the practical application condition, like The oil-filled capacitors are recommended in high temperature and high frequency working condition, like high frequency induction heating, high power AC filter circuit in power network etc. The dry capacitors are recommended in power electronics with normal temperature -40~70 and 50~60hz working enviroment.
Solid epoxy resin:
Advantages: lowcost.
Disadvantages: poor rejection of heat; If the metalize film of capacitor being breakdown, the generated heat and gas can’t be released from the solid epoxy resin, therefore when the heat and gas reach up to limit, it will strike to all directions, furtherly cause a burst on the top cover or middle part of capacitors. Also, Sometimes even the internal breakdown, the external and surface temperature rise is normal, but the capacitance value show fading.
Canola/castor oil or other vegetable oil：
Advantages: Super good heat dissipation, eco-friendly. The thermal conductivity of castor oil is about 80% higher than that of nitrogen and about 50% higherthan that ofthe polymerresin.
Disadvantages: Since the oil contains moisture, It requires a special process like vacuum filling process. The vacuum filling machinery is a large investment. It recommended for high voltage, high frequency, high current application usually.
Silicon oil:
Advantages: It has the best heat dissipation;
Disadvantages: high cost, more expensive than vagetable oil/canola oil. It is recommended for high voltage, high current, high frequency working condition. The application is similar to vegetable oil. It is popular to used for three-phase AC filter circuit. To make the life of the capacitors higher is important to dissipate the internal losses so that the power dissipated in the coil can come out in the external environment.
Paraffin wax:
The cost is between epoxy resin and vagetable oil. Since It has a low melting point, strong corrosive properties, and requires a relatively high processing technology to ensure the service life of the capacitor.
Advantages: Lowcost, eco-friendly,inactive gas. The internal pressure of a nitrogen-filled capacitor with good sealing performance basically does not change with temperature variations.
However, it has extremely high requirements for the sealing process of the casing. When the sealing performance is poor and nitrogen leaks, air enters the interior of the capacitor. The capacitor discharges impurities in the air, causing a significant decrease in capacitance value and easily leading to explosion-proof failure, capacitor explosion and fire, and other major problems.