The basic structure of a power capacitor includes the capacitor elements, impregnating agent, fasteners, leads, outer casing, and bushing. 

The structure is shown in Figure 1.

Figure 1: Structure Diagram of a Compensation Capacitor

1.Lead bushing

2.Lead connector plate

3.Connector plate

4.Flat element

5.Fixing plate

6.Insulator

7.Encapsulation component

8.Connecting clip

9.Clamp

10.Outer shell

Capacitors with a rated voltage below 1kV are called low voltage capacitors, and those above 1kV are called high voltage capacitors. Both types are made with a three-phase, delta connection, with internal elements connected in parallel, and each parallel element has its fuse; high voltage capacitors are generally made single-phase with internal elements in parallel. The outer casing is welded with sealed steel plates. The core is composed of capacitor elements connected in series and parallel, with the capacitor elements using aluminum foil as electrodes and composite film for insulation. The capacitor is filled with insulating oil (mineral oil or dodecylbenzene, etc.) as the impregnating medium.

(1) Capacitor Elements

These are made by winding solid medium of certain thickness and layers with aluminum foil electrodes. Several capacitor elements are connected in parallel and series to form the capacitor core. In high voltage capacitors with a voltage of 10kV and below, each capacitor element has a fuse in series for internal short-circuit protection of the capacitor. When an element fails, the other intact elements discharge to it, causing the fuse to rapidly melt in milliseconds, isolating the faulty element, allowing the capacitor to continue working normally.

(2) Impregnating Agent

The capacitor core is generally immersed in an impregnating agent to improve the dielectric strength of the capacitor elements, enhance partial discharge characteristics, and improve cooling conditions. Common impregnating agents include mineral oil, polychlorinated biphenyl (PCB), SF6 gas, etc.

(3) Outer Casing and Bushing

The outer casing is generally made of welded thin steel plates, coated with flame-retardant paint. The casing lid is welded with a lead bushing, and the side of the box is welded with climbing hooks, grounding bolts, etc. Large-capacity aggregate capacitors have an oil pillow or metal expander and pressure relief valve on the casing lid, and the side of the box is equipped with plate radiators, pressure-type temperature control devices, etc. The terminal leads are drawn from the lead porcelain bushing.