How Dielectric Film Selection Impacts Film Capacitor Performance and Reliability

In film capacitor manufacturing, electrical performance and long-term reliability are fundamentally determined by the quality of the dielectric film. While external dimensions and rated values are easy to specify, the real performance of a capacitor depends on how well the dielectric material performs under electrical stress, thermal cycling, and continuous operation.

For applications such as motor run capacitors, power supplies, and industrial electronics, proper dielectric film selection is not simply a material choice—it is a critical engineering decision that directly affects stability, efficiency, and service life.

The Role of Dielectric Film in Film Capacitors

The dielectric film acts as the insulating medium between capacitor electrodes and defines the capacitor’s fundamental electrical behavior. Its properties directly influence capacitance accuracy, insulation resistance, dielectric loss, and voltage withstand capability.

Key electrical parameters such as dielectric constant (εr) and dissipation factor (tan δ) determine how efficiently a capacitor stores and releases energy. A stable dielectric material ensures minimal energy loss and consistent performance across temperature and frequency ranges.

In practical applications, the dielectric film must also withstand repeated electrical stress without degradation. Poor film quality can result in increased losses, unstable capacitance, and reduced lifetime—issues that often appear only after long-term operation.

Key Electrical Properties of Dielectric Films

When selecting dielectric film for capacitors, several electrical characteristics must be carefully evaluated:

Dielectric Constant (εr): Determines capacitance value relative to film thickness and electrode area

Dissipation Factor (tan δ): Indicates dielectric losses and heat generation

Breakdown Strength: Defines maximum voltage withstand capability

Insulation Resistance: Affects leakage current and long-term stability

For high-reliability applications, low dielectric loss and high insulation resistance are essential to ensure safe and efficient operation over extended service life.

Mechanical and Surface Quality Requirements

Electrical performance alone is not sufficient. The mechanical stability and surface quality of the dielectric film play a crucial role during capacitor manufacturing and operation.

High-quality capacitor film must exhibit:

• Uniform thickness across the entire roll

• Smooth, defect-free surface

• Stable tensile strength suitable for winding

Surface defects such as micro-scratches, contamination, or thickness variations can create localized electric field concentrations. These weak points increase the risk of partial discharge and dielectric degradation, particularly under high voltage or high temperature conditions.

Mechanical consistency is also essential to maintain stable winding tension and prevent deformation during thermal cycling.

Common Dielectric Film Materials Used in Film Capacitors

Among various dielectric materials, polypropylene (PP) and polyester (PET) are the most commonly used in film capacitors.

Polypropylene (PP) Film

Polypropylene film is widely used in high-reliability and motor run capacitors due to its:

• Low dielectric loss

• High insulation resistance

• Excellent voltage withstand capability

• Stable capacitance over temperature

These characteristics make PP film ideal for applications requiring continuous operation and long service life.

Polyester (PET) Film

Polyester film offers higher dielectric constant and smaller size for the same capacitance value. It is often used where compact size is a priority, although it generally exhibits higher dielectric losses compared to polypropylene.

The choice between PP and PET films depends on application requirements, operating conditions, and performance expectations.

How Dielectric Film Affects Long-Term Reliability

Dielectric film quality has a direct impact on capacitor aging behavior. Over time, factors such as electrical stress, temperature rise, and environmental conditions can accelerate dielectric degradation if the film is not properly selected.

High-quality dielectric films help ensure:

• Stable capacitance under thermal cycling

• Low loss during continuous operation

• Reduced risk of insulation failure

• Extended operational lifetime

In contrast, inconsistent or unsuitable film materials may lead to gradual performance drift, increased losses, and eventual failure—often long after the capacitor has been installed in equipment.

From Dielectric Film Selection to Manufacturing Control

While dielectric film selection forms the foundation of capacitor performance, it is only the first step. To fully realize the benefits of high-quality film, strict manufacturing control is required throughout the production process.

At EVAE, dielectric films are carefully evaluated not only for electrical characteristics but also for mechanical consistency and long-term stability. This approach ensures that selected materials are compatible with precision manufacturing processes and real-world operating conditions.

However, even the best dielectric film cannot deliver optimal performance without proper manufacturing execution. In particular, precision winding quality plays a decisive role in converting material potential into reliable capacitor performance

Conclusion

Dielectric film selection is a critical factor in film capacitor design and manufacturing. Its electrical and mechanical properties directly influence performance, reliability, and service life.

By selecting the appropriate dielectric film and applying disciplined quality control, manufacturers can ensure that film capacitors meet the demands of modern industrial and power applications—not only at initial testing, but throughout their entire operational lifetime.