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Capacitance grading of cables means
Use of dielectrics in different concentration
Introduction of capacitance at various length of cable to counter the effect of inductance
Use of dielectrics of different permittivity
Grading according to capacitance per km length of the cable
Use of dielectrics of different permittivity
Capacitance grading in high-voltage cables refers to the technique of using multiple layers of dielectrics with different permittivities (epsilonrтАЛ) to ensure a uniform electric stress distribution across the cable insulation. By arranging materials with higher permittivity near the conductor and lower permittivity towards the sheath, the potential gradient is kept more uniform, allowing for better utilization of the dielectric material.
Capacitance grading in high-voltage cables refers to the technique of using multiple layers of dielectrics with different permittivities (epsilonrтАЛ) to ensure a uniform electric stress distribution across the cable insulation. By arranging materials with higher permittivity near the conductor and lower permittivity towards the sheath, the potential gradient is kept more uniform, allowing for better utilization of the dielectric material.
g=xln(R/r)VтАЛ тАФ Electric stress at distance x from the conductor center
╧╡1тАЛg1тАЛ=╧╡2тАЛg2тАЛ тАФ Condition for graded stress
In a homogeneous cable, the electric stress is maximum at the conductor surface and minimum at the sheath. By grading, we make the product of permittivity and electric field intensity (epsilonE) constant or at least more uniform across layers. This reduces the peak stress, preventing local breakdown of the dielectric and allowing for a reduction in the overall thickness of the cable insulation.
Used to make the electric field strength uniform across the cable dielectric.
Higher permittivity dielectric is placed near the conductor where stress is high.
Lower permittivity dielectric is placed near the metallic sheath.
Grading allows for thinner insulation, reducing cable size and cost.
Improved dielectric material utilization
Reduction in overall cable dimensions
Lower insulation breakdown risks
Increased manufacturing complexity
High cost of specialized dielectric materials
Interfaces between different dielectrics can become weak points
Extra High Voltage (EHV) cables
Underground transmission systems
Capacitance grading is primarily used to overcome the non-uniform stress distribution inherent in single-core cables.
Option B refers to inductive loading (e.g., Pupin coils), which is unrelated to cable dielectric grading.
C is correct тАФ Capacitance grading involves using dielectrics of different permittivity values to achieve a uniform electric stress profile across the cable insulation.
Remember: Capacitance grading balances electric stress (Dielectric constant), whereas inductive loading (Pupin coils) balances the line impedance.