Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
While laying 33 kV underground cable with the diameter D, minimum bending radius should be
12D
30D
100D
200D
30D
For underground cables, the minimum bending radius is specified to prevent damage to the insulation, metallic sheath, and armor due to excessive mechanical stress during installation. According to IS 1255 (Code of Practice for Installation and Maintenance of Power Cables up to 33 kV), the recommended bending radius is typically 15D for armored single-core cables and 30D for armored multi-core cables, where D is the overall diameter of the cable.
For underground cables, the minimum bending radius is specified to prevent damage to the insulation, metallic sheath, and armor due to excessive mechanical stress during installation. According to IS 1255 (Code of Practice for Installation and Maintenance of Power Cables up to 33 kV), the recommended bending radius is typically 15D for armored single-core cables and 30D for armored multi-core cables, where D is the overall diameter of the cable.
RminтАЛ=k├ЧD тАФ where RminтАЛ is the minimum bending radius, k is a constant based on cable construction/insulation, and D is the outer diameter.
When a cable is bent, the outer portion of the cable insulation is subjected to tensile stress, while the inner portion is subjected to compressive stress. If the bending radius is too small, these mechanical stresses exceed the elastic limit of the materials, leading to internal delamination, physical cracks in the XLPE or PILC insulation, and deformation of the metallic shield, which can cause partial discharge and eventual dielectric failure.
The factor k depends on the cable type (single-core vs. multi-core) and voltage grade.
Exceeding the bending limit can cause 'bird-caging' of the metallic wires.
Bending radius requirements are more stringent for high-voltage cables to preserve electric field uniformity.
Prevents mechanical fatigue of insulation
Maintains structural integrity of the metallic sheath
Ensures long-term dielectric performance
Requires larger cable ducts and trenches
Increases space requirement for cable joints and manholes
Distribution of power in congested urban areas
Connection between substations and industrial facilities
Power transmission in environments where overhead lines are impractical
IS 1255 guidelines are mandatory for power cable installations in India to ensure system reliability.
For unarmored cables, the bending radius limits are generally lower compared to armored cables because the armored layers significantly increase the cable's stiffness.
B is correct тАФ For 33 kV underground multi-core cables, the industry standard for the minimum bending radius is 30D to prevent dielectric damage during the laying process.
Always remember that bending radius constraints are inversely related to the flexibility of the cable; higher voltage cables (e.g., 33kV) are thicker and less flexible, necessitating larger bending radii.