What is the function of the porcelain bushing of a high-voltage capacitor?

In high-voltage power systems, capacitors are the key equipment for reactive power compensation, improving power factor, stabilizing grid voltage and reducing energy loss. And the high-pitched, white-bell-shaped porcelain components that we observe on the outer shell of high-voltage capacitors are actually porcelain bushings. So, what is their function exactly?

I. The Core Function of Ceramic Bushings

1. Insulation and Isolation (The most important and core function)

Internal insulation: The core of the capacitor is composed of multiple components connected in series and parallel. The working field strength is extremely high. The lead wires connecting the core have a very high potential difference (voltage) with the metal casing of the capacitor itself. The porcelain bushing serves as the outlet for the lead wires, and its interior and surface must be able to withstand this high pressure to prevent the lead wires from causing breakdown discharge to the casing.

External insulation: When operating outdoors, capacitors will encounter complex environments such as moisture, condensation, salt fog, and dirt. The porcelain bushing, with its outstanding arc resistance performance and extremely high insulation resistance, can effectively ensure that there is sufficient creepage distance and electrical clearance between the high-voltage lead and the grounded housing, preventing surface flashover (i.e., surface discharge) and avoiding short-circuit accidents.

2. Mechanical Support and Fixation

The porcelain bushing itself has high mechanical strength (resistance to compression and bending). It provides a firm support point for several heavy copper bars or cables, ensuring stable and reliable electrical connections and preventing the connection points from loosening, falling off or breaking due to the self-weight of the connection wires or external wind force, vibration, etc., thereby avoiding faults.

3. Sealing Protection

The impregnating agents of capacitors (such as insulating oil, SF6 gas, environmentally friendly gases, etc.) are the key media for ensuring the insulation and heat dissipation of internal components. They must be strictly sealed to prevent leakage and moisture absorption. The connection between the porcelain bushing and the capacitor housing (usually a steel plate) adopts a special sealing structure (such as rubber gaskets, metal welding, etc.), which matches the metal's expansion coefficient to ensure that the equipment maintains good sealing throughout its entire life cycle, isolating the outside air and moisture.

II. Why Choose "Porcelain" as the Material?

1. Extremely high electrical insulation strength: Excellent withstand voltage performance, capable of withstanding extremely high power frequency voltage and impulse voltage.

2. Excellent mechanical strength: Resistant to compression and bending, capable of withstanding huge electrical force and mechanical pressure.

3. Outstanding weather resistance: Anti-aging, corrosion-resistant, not affected by sunlight or rain, with a lifespan of several decades.

4. Excellent thermal stability: The thermal expansion coefficient is low, making it less likely to crack due to sudden temperature changes, and the thermal conductivity is moderate.

5. Strong anti-pollution capability: The surface is smooth and does not accumulate dust easily. Even if there is dirt, the numerous umbrella skirts in its design can effectively increase the creepage distance and prevent flashover.