Power cables, as critical components for transmitting electrical energy, are susceptible to external electromagnetic interference in complex electromagnetic environments, leading to signal distortion, reduced transmission efficiency, and even equipment failure. To address this issue, power cables typically employ shielding structures to suppress electromagnetic interference. The design principles and quantifiable effects of shielding are core issues for ensuring stable system operation.
The core function of the shielding layer is to construct an electromagnetic isolation barrier using metallic materials, blocking the coupling path between external interference fields and the internal conductor. Its mechanism can be divided into two categories: first, reflecting high-frequency electromagnetic waves back to the external environment through reflection; and second, converting electromagnetic energy into heat energy through absorption. This bidirectional suppression capability makes shielding a key means of reducing electromagnetic interference, especially in scenarios with strong electromagnetic interference such as industrial control, medical equipment, and communication base stations, where its performance directly determines the reliability of power cables.
The effectiveness of the shielding structure in suppressing electromagnetic interference is primarily reflected in the choice of materials. Metals with excellent conductivity, such as copper and aluminum, are the mainstream choices. Copper, due to its low resistivity and significant skin effect, performs better in suppressing high-frequency interference; aluminum, with its advantages of light weight and low cost, is suitable for cost-sensitive large-scale cabling scenarios. Furthermore, the use of composite materials such as the layering of copper and aluminum foil can address the suppression needs of both high-frequency and low-frequency interference, forming a wider-bandwidth protective barrier. Material thickness and purity are equally crucial; thicker shielding layers provide stronger absorption capabilities, while high-purity metals reduce energy loss due to impurities, thereby improving overall shielding effectiveness.
Weaving density is another core parameter affecting shielding layer performance. High-density braided structures increase the interlacing points of the metal wires, forming a denser electromagnetic isolation mesh, effectively reducing interference signal leakage. This structure is particularly suitable for high-frequency interference environments because the shorter wavelengths of high-frequency electromagnetic waves are more easily reflected or absorbed by the fine braid. In contrast, while low-density weaving is less expensive, it may lead to a decrease in shielding effectiveness due to excessively large gaps, especially in bending or vibration scenarios, where deformation of the braided structure further widens the gaps, requiring optimization of the weaving process or combination with other shielding methods to compensate.
Multi-layer composite shielding structures achieve comprehensive suppression of electromagnetic interference by layering shielding layers with different properties. For example, the inner layer uses a high-density braided layer to block high-frequency interference, the outer layer is wrapped with a metal foil layer to enhance low-frequency shielding, and an insulating layer is added in between to prevent interlayer short circuits. This layered design not only expands the shielding bandwidth but also improves the overall anti-interference capability through the synergistic effect of each layer. Especially in complex electromagnetic environments, the multi-layer structure can separately cope with interference from different sources, such as power line harmonics, radio signals, and motor arcs, ensuring that power cables can still transmit stably under multi-band interference.
Grounding quality is a key factor determining the actual effectiveness of the shielding layer. Good grounding can conduct the interference current absorbed by the shielding layer into the ground, preventing it from forming secondary interference between conductors. If the grounding is poor, the shielding layer may become a new source of interference due to charge accumulation, or even exacerbate electromagnetic coupling effects. Therefore, the shielding layer needs to be reliably connected to the equipment ground wire through a low-impedance path. The grounding point should be selected to avoid areas with strong interference and ensure that the grounding resistance meets the standard requirements. In addition, multi-point grounding strategies can reduce interference caused by grounding loops in high-frequency scenarios, while single-point grounding is suitable for low-frequency environments, and should be flexibly selected according to the specific application scenario.
In practical applications, the effectiveness of power cable shielding needs to be quantitatively evaluated through standardized testing. Testing is typically conducted in a shielded room, using a signal generator to simulate interference sources of different frequencies and intensities. A spectrum analyzer is used to measure parameters such as signal attenuation and noise levels before and after shielding. Test results are expressed as shielding effectiveness, i.e., the power ratio of the interference signal before and after shielding; a higher value indicates better shielding. Through such testing, shielding structure parameters can be optimized to ensure that power cables meet the electromagnetic compatibility requirements of specific scenarios, providing a reliable guarantee for stable equipment operation.
