Why Shape of the Cables Are Round

The round shape of cables is not a mere choice but a result of extensive engineering and material science considerations. In this article, we delve into the specifics of why cables are designed in round shapes, primarily focusing on their insulating materials, dielectric strength, and the practical benefits they offer.

Insulating Material and Voltage Rating

For cables with a voltage rating of up to 1100V, a sector-shaped conductor is often employed to economize on the insulating material and reduce overall diameter. However, this is not the case for higher voltage applications, as illustrated by the history of power cable insulation materials.

Past Use of Insulating Oil

Up until the mid-seventies, paper impregnated with insulating oil was the common choice for insulating cores in high-voltage power cables, generally ranging up to 11kV. For these applications, the cores were designed in a circular shape rather than a sector shape. Each core was then wrapped with a thin metallic strip that was earthed, ensuring that each core only had to handle a voltage of approximately 6350.85V (11000 / 1.732). This circular design ensured a uniform distribution of electrostatic flux, thereby enhancing the longevity of the cable.

Evolution to Cross-Linked Polyethylene (CLP)

As Cross-Linked Polyethylene (CLP) was discovered to have higher dielectric strength, it quickly became the preferred insulating material for power cables. CLP insulated cables always feature circular-shaped conductors, which come with an additional semiconducting outer layer for even distribution of electrostatic flux. In a CLP-insulated cable, the stranded conductor is molded into a segment of a circle, allowing all cores to form a complete circle when assembled. This circular design ensures uniform electrostatic flux distribution and reduces wear and tear, particularly at sharp edges.

Key Benefits of Circular Shape

Uniform Electric Field and Reduced Corona Effect

In shapes with corners, the electric field E is not uniform. The circular shape, devoid of corner points, ensures a uniform electric field, reducing the likelihood of corona discharge, a damaging effect caused by high electric fields near sharp points.

Reduced Wear and Tear

Round wires are less likely to cause wear and tear due to their smooth surface. They have fewer edge points compared to other shapes, which means they are less prone to touching and causing damage to soft parts. This smoothness also reduces energy loss that typically occurs with sharp edges, making round sections more efficient in terms of power transmission.

Easier Manufacturing and Maintenance

Manufacturing and maintaining round-section wires are generally easier and more straightforward compared to other shapes. This ease of manufacturing and maintenance makes round cables more practical for widespread use in various industries.

For further in-depth study, you may refer to the following link for detailed insights into the design considerations of power cables: POWER CAB.

Conclusion

The round shape of cables serves multiple practical purposes, from enhancing cable longevity and efficiency to ensuring easier manufacturing and maintenance. Understanding these considerations can help in the development of more robust and efficient cable systems.