The basic structure of power capacitor includes: capacitor element, impregnant, fastener, lead, shell and bushing.

The rated voltage below 1kV is called low-voltage capacitor, and the rated voltage above 1kV is called high-voltage capacitor. They are all made into three-phase and triangular connection lines, and the internal components are in parallel, and each parallel component has a separate fuse; the high-voltage capacitor is generally made into single-phase, and the internal components are in parallel. The shell is welded with sealed steel plate, and the core is composed of series and parallel capacitor elements. The capacitor elements are insulated with composite film with aluminum foil as electrode. The insulating oil (mineral oil or Dodecylbenzene, etc.) of capacitor underwear is used as impregnating medium.

(1) Capacitance element

It is made of a certain thickness and number of layers of solid medium and aluminum foil electrode. Several capacitor elements are connected in parallel and series to form a capacitor core. In the high voltage capacitor with voltage of 10kV and below, each capacitor element is connected with a fuse in series, which is used as the internal short circuit protection of the capacitor. When a component breaks down, other intact components will discharge it, so that the fuse will fuse rapidly in millisecond level, and the faulty component will be removed, so that the capacitor can continue to work normally. The structure of the capacitor is shown in Figure 2.

(2) Impregnant

The core of capacitor is usually placed in impregnant to improve the dielectric withstand strength, partial discharge characteristics and heat dissipation conditions of capacitor components. The impregnating agents generally include mineral oil, chlorinated biphenyl, SF6 gas, etc.

(3) Shell and sleeve

The shell is generally made of thin steel plate welded, the surface is coated with flame retardant paint, the shell cover is welded with outlet sleeve, and the side of the box wall is welded with hanger and grounding bolt. Oil conservator or metal expander and pressure relief valve are also installed on the tank cover of large capacity collective capacitor. Sheet radiator and pressure type temperature control device are installed on the side of the tank wall. The terminal is led out from the porcelain bushing.