What is a self-healing shunt capacitor -Working principle and application

What is a self-healing shunt capacitor

Self-healing capacitors are characterized by their self-healing properties. When the dielectric breaks down, the short-circuit current will melt and evaporate the metal film around the breakdown site, thereby restoring insulation, so it has high operational reliability.The time required for self-healing after dielectric breakdown is only a few microseconds. When the weak point of the capacitor inside the dielectric breaks down to form a path, an arc is formed in a very short time, causing the local temperature and pressure to rise sharply, and the metal layer evaporates violently. The self-healing radius expands, the arc is pulled off, and a circular area centered on the breakdown point that loses the metal coating is formed on the surface of the dielectric, and the self-healing process is completed. Opening the damaged self-healing capacitor, it can be found that the self-healing effect is especially at the edge of the dielectric in the capacitor.

BSMJ type self-healing low-voltage shunt capacitor capacitance tolerance is -5% ~ +10%, three-phase phase balance 《1.08.

Scope of application

BSMJ type self-healing low-voltage shunt capacitor is a capacitor unit and capacitor bank specially used to improve the power factor of the ac power system with a nominal voltage below 1kV and a frequency of 15Hz-60Hz.

How a self-healing shunt capacitor works

Self-healing low-voltage shunt capacitors are more complex.

There are many types of capacitors, such as aluminum electrolytic capacitors, solid capacitors, safety capacitors, and cbb capacitors.

The main working principle of self-healing low-voltage shunt capacitors is to adjust frequency and change power through capacitance absorption, and make electrical devices play a better role. So in general, the function of the self-healing low-voltage shunt capacitor is to adjust the frequency and change the power through capacitance absorption to make the electrical appliance more stable.

The components used in dry-type self-healing high-voltage shunt capacitors are self-healing capacitor components. Ordinary aluminum foil capacitor elements are made by sandwiching an insulating medium (film-paper composite or full film) between two layers of aluminum foil electrodes through rolling, pressing, welding, vacuum drying and liquid immersion.Due to the electric weakness of the medium, in order to avoid the short circuit of the two electrodes caused by the breakdown of the medium, more than two layers of the medium must be used, so that the electric weakness of each layer of the medium is staggered. The self-healing capacitor is different. Its medium is a single-layer polypropylene film, and a thin layer (less than 1/100 μm) of metal is evaporated on the surface as a conductive electrode.When a voltage is applied, the electrical weakness of the polypropylene film is broken down, and the breakdown current will pass through the breakdown point. Due to the sharp increase of the current density of the conductive metallized coating and the high heat generated by the metallized layer, the metal conductor around the breakdown point evaporates and dissipates rapidly, forming a blank area of the metal coating, and the breakdown point automatically restores insulation. The dielectric film produces a very small hole with a diameter of about a few microns, and the area of the metallized coating that disappears during the self-healing process is about a few millimeters in diameter.

According to the requirements of self-healing performance, the thinner the metallized plate coating of the capacitor, the better. The thinner the coating, the lower the energy generated during self-healing, the smaller the temperature rise, the smaller the damage to the capacitor, and the better the self-healing property is.However, according to the relationship between dielectric strength and coating resistance (see attached picture), the thinner the coating, the greater the contact resistance, the greater the breakdown field strength, and the greater the contact resistance, the severe heating will occur.Under the action of closing inrush current, the capacitor will cause overheating damage to the contact parts, resulting in failure of the capacitor.Therefore, solving the above-mentioned contradictions is the key point in the manufacture of dry self-healing capacitors. Now, there are many ways to solve this problem. For example, Jinzhou Capacitor Factory adopts a unique coating process - trapezoidal coating edge thickening technology, which gradually thins the metallized coating over a large area and thickens the electrode lead-out edge, which not only improves the breakdown field strength, but also reduces capacitance loss. At the same time, the surge resistance capability of the components is improved.

Self-healing shunt capacitor function

Self-healing low-voltage shunt capacitors (MKPS.BSMJ/BCMJ/BZMJ) are suitable for parallel connection with loads in AC power systems with a power frequency of 50HZ or 60HZ and a rated voltage of 1000V and below, so as to improve the power factor of the system, reduce line losses, improve voltage quality and give full play to the efficiency of power generation and power supply equipment;On-site compensation of inductive equipment such as motors, transformers, and power frequency electric furnaces; electric traction locomotives, UPS systems, and harmonic filtering of power systems, etc.