Self-healing low-voltage parallel cylindrical power capacitors require multiple technical measures to ensure their performance stability and service life in frequent switching scenarios. Frequent switching causes the capacitor to undergo repeated charge and discharge cycles, generating transient current surges and voltage fluctuations, which can lead to dielectric aging, excessive temperature rise, and mechanical stress damage. To address these issues, a comprehensive protection system must be constructed encompassing four key aspects: material properties, structural design, protection mechanisms, and control strategies.
The core advantage of self-healing low-voltage parallel cylindrical power capacitors lies in their self-healing mechanism. When the metallized polypropylene film dielectric experiences a localized breakdown, the metal layer surrounding the breakdown point rapidly evaporates due to arcing, forming an insulating isolation zone and restoring dielectric performance. This feature enables them to automatically repair minor damage during frequent switching, preventing the breakdown point from expanding and potentially causing capacitor failure. However, the self-healing process consumes some dielectric material, and long-term frequent switching can accelerate material aging. Therefore, optimizing the metallized film formulation and thickness is crucial to improve its dielectric strength and self-healing efficiency, thereby extending dielectric life.
In terms of structural design, the cylindrical aluminum can package and fully sealed structure provide the capacitor with excellent mechanical support and environmental isolation. The aluminum can casing effectively shields external electromagnetic interference. A pressure-isolating device safely releases pressure in the event of an internal fault, preventing explosion risk. A built-in discharge resistor quickly dissipates residual voltage after the capacitor is powered off, ensuring safe operation. Furthermore, the capacitor core is wound using high-quality metallized polypropylene film, with strict control of winding tension and interlayer gaps to prevent mechanical deformation and dielectric damage, thereby enhancing resistance to switching shocks.
Protection mechanisms are key to ensuring frequent switching performance. Overvoltage protection uses a set operating voltage threshold. When the grid voltage exceeds the rated value, the protection device quickly disconnects the capacitor from the grid, preventing dielectric breakdown due to overvoltage. Overcurrent protection monitors current changes using fuses or electronic protectors, quickly disconnecting the circuit in the event of a short circuit or overload, preventing capacitor damage due to overheating. Temperature protection uses a built-in sensor to monitor the internal temperature of the capacitor in real time. When the temperature exceeds the allowable limit, an alarm or shutdown is triggered to prevent thermal runaway. Harmonic protection addresses harmonic interference in the grid by detecting harmonic content and adjusting the capacitor switching strategy to avoid resonant overload.
Optimizing control strategies can significantly reduce the damage caused by frequent switching on and off of capacitors. The intelligent controller uses a cyclic switching algorithm to balance the number of times each capacitor group is used, preventing excessive switching of a single group. Furthermore, a switching delay function is provided to ensure that capacitors are fully discharged before being re-connected after a power outage, preventing overcurrent shocks caused by residual voltage. For grids with high harmonic content, series reactors can be configured. By adjusting the parameters of the capacitors and reactors, harmonic resonance can be suppressed and the risk of capacitor overload can be reduced.
Heat dissipation design is crucial to ensuring performance in frequent switching scenarios. Capacitors generate heat during charging and dissipation. Poor heat dissipation can lead to excessive temperature rise and accelerated dielectric aging. The cylindrical aluminum can shell dissipates heat through natural convection and radiation, meeting the heat dissipation requirements under general operating conditions. In high-temperature or high-density switching scenarios, forced air cooling or liquid cooling is required to enhance heat dissipation efficiency. Furthermore, capacitors should be installed with sufficient spacing to avoid heat accumulation and ensure good ventilation to prevent performance degradation due to high ambient temperatures.
Material selection and process control are fundamental to improving capacitor switching resistance. Metallized polypropylene film must possess high dielectric strength, low loss tangent, and excellent self-healing properties to withstand dielectric damage caused by frequent switching. The winding process requires precise control of tension and interlayer gaps to prevent dielectric deformation caused by mechanical stress. Using pollution-free insulating oil as the impregnant improves the capacitor's partial discharge performance and heat dissipation efficiency, thereby extending its service life.
Ensuring the performance of self-healing low-voltage parallel cylindrical power capacitors in frequent switching scenarios requires comprehensive optimization of self-healing mechanisms, structural design, protection mechanisms, control strategies, heat dissipation design, and material processing. By improving dielectric strength, strengthening mechanical support, improving protection functions, optimizing switching logic, and enhancing heat dissipation capabilities, damage to the capacitors caused by frequent switching can be effectively reduced, ensuring stable operation and long life under complex operating conditions.
