As a key component for motor starting and operation, the performance of ac motor capacitors directly affects the efficiency and reliability of the motor. As one of the core technologies of modern ac motor capacitors, the self-healing property significantly extends the service life of the equipment by quickly restoring the insulation capacity.
The self-healing property is based on the dielectric structure of metallized film ac motor capacitors. When ac motor capacitors break down due to overvoltage or local defects, the high current density near the breakdown point causes the metal coating to vaporize instantly, forming an insulating gap and blocking the current path. This process is usually completed within a few microseconds and does not spread to the surrounding area, thus avoiding complete dielectric failure. For example, when polypropylene metallized film breaks down, the local temperature can reach thousands of degrees Celsius, but the blank area formed after the metal evaporates can quickly restore insulation.
The self-healing property delays the overall aging of ac motor capacitors by reducing the dielectric damage area. After the breakdown of traditional ac motor capacitors, the insulation layer will continue to deteriorate, resulting in a decrease in capacity or short circuit; while self-healing ac motor capacitors only form tiny defects at the breakdown point, and after each self-healing, the remaining dielectric can still work normally. Studies have shown that the failure time of self-healing ac motor capacitors under the same working conditions is 3-5 times longer than that of non-self-healing types.
The number of self-healing times is not infinite. Each self-healing will increase dielectric loss, slightly reduce capacity, and may cause local overheating. When the number of self-healing times exceeds the critical value (usually thousands of times), the dielectric performance will accelerate deterioration and eventually cause catastrophic failure. Therefore, although the self-healing property extends the average life, its long-term reliability needs to be evaluated in combination with failure mode analysis (FMEA).
High temperature and high humidity environment will weaken the self-healing ability. High temperature accelerates dielectric aging, reduces the adhesion of metal plating, and leads to incomplete insulation recovery after self-healing; excessive humidity may cause local discharge and expand the breakdown range. For example, in an environment of 85℃, the life of self-healing ac motor capacitors is only 1/80 of that at 60℃. Therefore, it is necessary to improve environmental adaptability by optimizing the packaging design (such as epoxy resin potting).
Long-term overvoltage operation will reduce the self-healing threshold and make ac motor capacitors more prone to breakdown. For example, when the operating voltage exceeds 1.1 times the rated value, the number of self-healing times may increase by more than 10 times, resulting in a significant shortening of the lifespan. Therefore, it is necessary to ensure that the ac motor capacitors operate within the range of 90%-105% of the rated voltage through voltage monitoring and reactive power compensation systems.
The use of gradient square resistance metallized film can balance self-healing and current carrying capacity. By doping alloy elements in the plating layer, the square resistance decreases with increasing thickness, which not only ensures the self-healing speed but also avoids overheating. For example, after a certain brand of ac motor capacitors adopted this technology, the self-healing life was extended by 40%, and the capacity stability was improved by 25%. In addition, optimizing the thickness of the dielectric layer (such as controlling the thickness of the polypropylene film to 5-10μm) can further improve the self-healing efficiency.
By regularly testing the equivalent series resistance (ESR) and capacity change rate of ac motor capacitors, early warning of self-healing capacity degradation can be given. When the ESR value exceeds 200% of the initial value or the capacity decreases by more than 5%, it is recommended to replace the ac motor capacitors. In addition, dynamically adjusting the switching strategy of AC motor capacitors in combination with motor load characteristics (such as starting frequency and load rate) can reduce the number of ineffective self-healing times and extend the overall life.
The self-healing property provides AC motor capacitors with "self-repair" capabilities through the combination of physical mechanisms and material science, significantly improving equipment reliability. However, its application needs to be combined with environmental control, voltage management and material innovation to maximize its life. In the future, with the development of nano-composite media and intelligent monitoring technology, self-healing AC motor capacitors are expected to play a more critical role in industrial automation, new energy and other fields.
