With the increase in electricity load, there is an inevitable requirement to improve the utilization rate of the power grid system. Because reactive current occupies a portion of the effective power transmission capacity and increases power transmission losses, it is crucial to minimize the distance between reactive power generation and reactive power users. This increases the capacity to transmit active power, reduces energy loss, and improves the quality of transmitted power. Most electrical appliances connected to the power grid require not only active power but also a certain amount of reactive power. The magnetic field in motors and transformers is maintained by reactive current, the inductance in transmission lines also consumes reactive power, and all inductive circuits such as reactors and fluorescent lamps require a certain amount of reactive power. To reduce losses in power transmission and improve the capacity and quality of power transmission, reactive power compensation is necessary. I. The Compensation Function of Power Capacitors In principle, a capacitor is equivalent to a generator that produces capacitive reactive current. Connecting it to a compensation device or equipment that requires reactive power reduces the load on the transformer and output lines, thereby increasing the output active power capacity. Under a certain output active power, the losses in the power supply system are reduced. Comparatively, capacitors are the simplest and most economical method to reduce the load on transformers, power supply systems, and industrial power distribution. Therefore, capacitors are imperative for reactive power compensation in power systems. II. Structural Characteristics of Self-Healing Low-Voltage Parallel Power Capacitors For many years, oil-impregnated paper capacitors have been widely used for reactive power compensation on the low-voltage side. These capacitors are large, have high losses, are expensive, and are prone to explosions, bulging, and oil leaks, making them far from meeting the requirements of power grid development. In recent years, self-healing low-voltage parallel power capacitors have been developed. These capacitors use electrical-grade polypropylene film as the dielectric, with a single-sided metal film deposited as the electrode. The elements are formed using a non-inductive winding method, and metal is sprayed onto both ends, with the electrode plates led out as leads. The element is the main body of the capacitor and its key component. According to the capacity requirements, a certain number of elements are combined with wires, insulated, and equipped with explosion-proof devices. They are then placed in a casing and processed to form a single capacitor. The capacitor should have a discharge device that can reduce the residual voltage on the capacitor to zero within a specified time after disconnection from the power supply, ensuring the safety of maintenance personnel and preventing overvoltage caused by voltage superposition during repeated switching. Although self-healing low-voltage parallel power capacitors have a self-healing function and are relatively safe and reliable, self-healing failures can still occur, leading to a decrease in the insulation level of the components, or even short circuits, resulting in bulging, explosions, and other isolated incidents. To address this issue, different manufacturers have adopted different explosion-proof measures. 1. Differential Pressure Explosion-Proof Device: When the insulation level of a component of the capacitor decreases, abnormal heat will inevitably be generated, increasing the internal pressure and causing the capacitor shell to deform and expand. The mechanical displacement may then break the explosion-proof sheet (wire). Since the power supply is connected to the capacitor component through the explosion-proof sheet, the disconnection of the explosion-proof sheet is equivalent to the power supply being disconnected. The explosion-proof effect depends on the design and installation position of the explosion-proof sheet and the sealing performance of the capacitor. 2. Safety Membrane: A metallized thin film is vapor-deposited into a mesh structure, dividing the capacitance of the capacitor component into a considerable number of small capacitors connected in parallel. Each small capacitor is vapor-deposited with a current fuse structure. When self-healing fails at a weak point in a small capacitor of the capacitor component, the current fuse of that small capacitor melts, and the component is deactivated, while the overall capacitance of the component decreases only slightly. 3. Temperature-current type fuse capacitors are composed of multiple capacitor elements. If each element is equipped with a temperature-current fuse, when the insulation of a certain element deteriorates due to self-healing failure, or even short-circuits, an overheating current will be generated, triggering the temperature-current fuse to operate. That element will immediately stop operating, while the entire capacitor can continue to operate normally, with only a slight decrease in capacitance. Explosion-proof measures are necessary, but the most important thing is to improve the reliability of capacitor elements. Manufacturers generally attach great importance to material selection and process control. Without excellent raw materials and strict process control, it is impossible to produce high-quality finished capacitors. Metallized film is a key raw material in capacitor production. Currently, Al metallized polypropylene film and Zn-Al (or Ag-Zn) polypropylene metallized film are generally used in the production of self-healing low-voltage parallel power capacitors. III. Differences between Aluminum Metallized Film and Zinc-Aluminum Metallized Film In coating technology, aluminum film is widely used because of its low production cost, strong environmental adaptability, ability to maintain conductivity for a long time under normal temperature and humidity conditions, good self-healing properties, and ease of storage and operation. One of the most prominent features of metallized capacitors is their excellent self-healing property. This means that when a weak point in the dielectric is broken down, the high energy generated by the short circuit causes the metal plating near the breakdown point to rapidly dissipate, creating a blank area and restoring insulation. This characteristic requires a relatively thin metallized film plating. However, in metallized capacitors, the metal plating acts as the electrode, and based on the principle of metal conductivity, a thicker plating is preferable to withstand high current surges. The gold plating material can only be Al, Zn, or their alloys. Under the influence of an electric field, electrochemical corrosion exists at the contact surfaces of different metals. Combined with the plating, poor contact at the gold-plated surface results in poor current surge resistance. Furthermore, aluminum film capacitors are prone to plating corrosion and peeling due to thermoelectric effects, leading to decreased capacitance, increased losses, and heat generation. Vapor deposition employs an edge thickening technique, resulting in a higher sheet resistance at the electrode and a lower sheet resistance at the gold-plated contact area. This resolves the contradiction between self-healing and resistance to high current surges. Moreover, the gold plating material uses the same Zn as the electrode, eliminating electrochemical corrosion. Vacuum coating results in less damage. Therefore, Zn-Al metallized film capacitors exhibit stable performance, low capacitance degradation, strong impact resistance, and long service life. However, Zn-Al films have short exposure times to air, are prone to oxidation, and require strict processing. Improper handling can increase losses due to electrothermal effects, affecting their service life. IV. Capacitor Quality Qualified self-healing low-voltage parallel power capacitors should conform to GB12747-91 standards. Before leaving the factory, all capacitor components are inspected and screened; only qualified components are allowed to assemble the capacitor. The capacitance, loss, withstand voltage, and insulation of the entire capacitor are tested, and the appearance is inspected and approved before leaving the factory. Capacitors leaving the factory should meet the technical specifications in the accompanying instruction manual. If a capacitor experiences breakdown, overheating, significant bulging, or failure within the warranty period, the manufacturer should replace it. V. Usage Precautions It is worth mentioning that users often neglect the instruction manual; therefore, the usage precautions should be carefully understood and followed during installation. As we all know, the impedance of a capacitor is inversely proportional to the frequency. As the frequency increases, the loss also increases. Measures must be taken to limit harmonics and inrush currents in the circuit. Capacitors always generate heat, so special attention must be paid to ventilation and cooling. After the reactive power compensation device is installed, during the trial operation, the system must be tested. If overvoltage, overcurrent, oscillation, harmonics, etc., are found, timely measures must be taken. This is essential for the normal operation of the capacitor.