The crack of high voltage ceramic capacitors can generally be classified into three categories. During the usage of these capacitors, fractures may occur, which often puzzles many experts. These capacitors were tested for voltage, dissipation factor, partial discharge, and insulation resistance during the purchase, and all passed the tests. However, after six months or a year of usage, some high voltage ceramic capacitors were found to have crackd. Are these fractures caused by the capacitors themselves or external environmental factors?

 

In general, the crack of high voltage ceramic capacitors can be attributed to the following three possibilities:

 

The first possibility is thermal decomposition. When capacitors are subjected to instantaneous or prolonged high-frequency and high-current working conditions, the ceramic capacitors may generate heat. Although the heat generation rate is slow, the temperature rises rapidly, leading to thermal decomposition at high temperatures.

 

The second possibility is chemical degradation. There are gaps between the internal molecules of the ceramic capacitors, and defects such as cracks and voids may occur during the capacitor manufacturing process (potential hazards in the production of inferior products). In the long run, some chemical reactions can produce gases such as ozone and carbon dioxide. When these gases accumulate, they can affect the outer encapsulation layer and create gaps, resulting in crack.

 

The third possibility is ion breakdown. High voltage ceramic capacitors rely on ions actively moving under the influence of an electric field. When ions are subjected to a prolonged electric field, their mobility increases. In the case of excessive current, the insulation layer can be damaged, leading to breakdown.

 

Usually, these failures occur after approximately six months or even a year. However, products from manufacturers with poor quality may fail after only three months. In other words, the lifespan of these high voltage ceramic capacitors is only three months to one year! Therefore, this type of capacitor is generally not suitable for critical equipment such as smart grids and high-voltage generators. Smart grid customers usually require capacitors to last for 20 years.

 

To extend the lifespan of capacitors, the following suggestions can be considered:

 

1)Replace the dielectric material of the capacitors. For example, circuits originally using X5R, Y5T, Y5P, and other Class II ceramics can be replaced with Class I ceramics like N4700. However, N4700 has a smaller dielectric constant, so capacitors made with N4700 will have larger dimensions for the same voltage and capacitance. Class I ceramics generally have insulation resistance values more than ten times higher than Class II ceramics, providing much stronger insulation capability.

 

2)Choose capacitor manufacturers with better internal welding processes. This involves the flatness and flawlessness of ceramic plates, the thickness of silver plating, the fullness of ceramic plate edges, the quality of soldering for leads or metal terminals, and the level of epoxy coating encapsulation. These details are related to the internal structure and appearance quality of the capacitors. Capacitors with better appearance quality usually have better internal manufacturing.

 

Use two capacitors in parallel instead of a single capacitor. This allows the voltage originally borne by a single capacitor to be distributed among two capacitors, improving the overall durability of the capacitors. However, this method increases costs and requires more space for installing two capacitors.

 

3)For extremely high voltage capacitors, such as 50kV, 60kV, or even 100kV, the traditional single ceramic plate integrated structure can be replaced with a double-layer ceramic plate series or parallel structure. This utilizes double-layer ceramic capacitors to enhance the voltage withstand capability. This provides a sufficiently high voltage margin, and the larger the voltage margin, the longer the predictable lifespan of the capacitors. Currently, only HVC company can achieve the internal structure of high voltage ceramic capacitors using double-layer ceramic plates. However, this method is costly and has high production process difficulty. For specific details, please consult the sales and engineering team of HVC company.