The shielding layer design of the composite shielded insulated tubular busbar body is the core element in ensuring its electromagnetic shielding effect. Its core logic lies in constructing a complete electromagnetic protection system through the synergistic effect of multiple shielding structures. This system must not only suppress the impact of external electromagnetic interference on the composite shielded insulated tubular busbar body, but also prevent electromagnetic radiation generated during busbar operation from interfering with surrounding equipment and the environment, thereby ensuring the stability and safety of power transmission.
The shielding layer design typically employs a three-layer structure: a conductor shielding layer, an insulating shielding layer, and a metallic shielding layer. The conductor shielding layer, usually made of semiconductor material, directly wraps around the conductor surface. Its function is to improve the electric field distribution and avoid partial discharge caused by concentrated electric fields on the conductor surface. For example, when the busbar transmits high voltage, the electric field strength at the conductor edges may be much higher than in the center. Without a conductor shielding layer, corona discharge or breakdown can easily occur at the edges. A semiconductor material conductor shielding layer, however, can control the electric field strength within a safe range by balancing the electric field distribution.
The insulating shielding layer, located between the main insulation layer and the metallic shielding layer, is also made of semiconductor materials, but its function focuses more on controlling the potential difference between the insulation layer and the metallic shielding layer. While the main insulation layer isolates the conductor from external electrical connections, a significant potential difference across the insulation layer can still lead to partial discharge or insulation aging. The insulating shielding layer controls the potential difference within a safe threshold by progressively attenuating leakage current, thereby extending the lifespan of the main insulation layer and improving the overall reliability of the composite shielded insulated tubular busbar body.
The metallic shielding layer is a key barrier for electromagnetic shielding, typically made of highly conductive aluminum alloy or copper foil, tightly wrapped around the main insulation layer to form a continuous conductor. Its mechanism of action includes two aspects: first, reducing the impact of external electromagnetic interference on the composite shielded insulated tubular busbar body by reflecting electromagnetic waves; and second, preventing leakage of electromagnetic radiation generated during busbar operation. The conductivity of the metallic shielding layer directly affects the shielding effect; the stronger the conductivity, the more significant the reflection and absorption capabilities of electromagnetic waves. Furthermore, the metal shielding layer must be grounded to direct electromagnetic interference to the ground, preventing secondary interference caused by the accumulation of charge within the shielding layer itself.
The manufacturing process of the shielding layer is crucial to its shielding effectiveness. For example, conductor and insulating shielding layers often employ a co-extrusion process, where semiconductor materials are melted and plasticized at high temperatures, uniformly coating the surface of the conductor or insulation layer to ensure a gap-free and bubble-free environment between the shielding layer and the encapsulated material. Impurities or bubbles present during processing can create localized electric field concentration points, reducing the insulation performance of the shielding layer. The manufacturing of metal shielding layers requires attention to continuity and fit to avoid breaks or loosening, which would weaken its shielding effect against electromagnetic waves.
The thickness design of the shielding layer must balance shielding effectiveness with cost-effectiveness. While an excessively thick shielding layer can improve shielding performance, it increases material costs and the weight of the composite shielded insulated tubular busbar body; conversely, an excessively thin shielding layer may not effectively suppress electromagnetic interference. Therefore, the thickness parameters of the shielding layer must be comprehensively evaluated based on the voltage level, transmission capacity, and operating environment of the composite shielded insulated tubular busbar body during the design phase. For example, the shielding layer thickness of a high-voltage composite-shielded insulated tubular busbar body is typically greater than that of a low-voltage busbar to cope with higher electric field strength and electromagnetic interference risks.
The grounding design of the shielding layer is the final step in ensuring the effectiveness of electromagnetic shielding. The metallic shielding layer needs to be connected to the grounding grid through a low-impedance path to ensure that electromagnetic interference can be quickly conducted to the ground. If the grounding resistance is too high, the charge accumulated in the shielding layer may form secondary electromagnetic radiation, which may exacerbate the interference problem. Therefore, the grounding design should use highly conductive grounding materials and optimize the grounding path to reduce grounding resistance and inductance, thereby improving the overall effectiveness of the shielding layer.
