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In the underground cables, electrostatic stress is
Maximum at conductor surface and minimum at the sheath
Minimum at conductor surface and maximum at the sheath
Same at the conductor and sheath
Zero at the conductor as well as on the sheath
Maximum at conductor surface and minimum at the sheath
In an underground cable, the electrostatic stress (or electric field intensity) is not uniform across the dielectric. Due to the cylindrical geometry of the cable, the electric field is inversely proportional to the radial distance from the center, resulting in a maximum value at the conductor surface and a minimum value at the lead sheath.
In an underground cable, the electrostatic stress (or electric field intensity) is not uniform across the dielectric. Due to the cylindrical geometry of the cable, the electric field is inversely proportional to the radial distance from the center, resulting in a maximum value at the conductor surface and a minimum value at the lead sheath.
gmaxтАЛ=rln(R/r)VтАЛ тАФ Stress at conductor surface
gminтАЛ=Rln(R/r)VтАЛ тАФ Stress at sheath inner surface
The electric field intensity g at a distance x from the center of a cable is given by gxтАЛ=xln(R/r)VтАЛ. As x increases from the conductor radius r to the sheath radius R, the denominator xln(R/r) increases, causing the field intensity gxтАЛ to decrease. Therefore, the stress is highest at the conductor surface (x=r) and lowest at the inner surface of the sheath (x=R).
Stress distribution is non-uniform in single-core cables.
Higher dielectric strength is required near the conductor.
Grading of cables is used to make the stress distribution more uniform.
Underground cables are immune to lightning surges.
Aesthetically superior and safe for urban areas.
Higher initial cost compared to overhead lines.
Difficult to locate and repair faults.
Urban power distribution.
High-voltage transmission in congested areas.
The ratio R/r determines the severity of the stress concentration.
Option B is incorrect because it describes an inverse scenario (capacitive field intensity follows an inverse radial law).
Capacitance grading and inter-sheath grading are methods used to mitigate high stress at the conductor.
A is correct тАФ The electrostatic stress in an underground cable is highest at the conductor surface and decreases as one moves towards the lead sheath.
Remember that in any cylindrical geometry involving radial fields, the field intensity is inversely proportional to the radius; hence, the smallest radius (conductor) always experiences the highest stress.