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Power factor of an open-ended cable can be improved by
Increasing the capacitance
Decreasing the capacitance
Increasing the conductor resistance
Increasing the insulation resistance
Increasing the insulation resistance
In an open-ended cable, the insulation resistance acts as a parallel resistive path to the leakage capacitance. Increasing the insulation resistance (RiтАЛ) reduces the leakage current component, which effectively improves the power factor of the cable towards unity by minimizing the ohmic losses associated with the insulation.
In an open-ended cable, the insulation resistance acts as a parallel resistive path to the leakage capacitance. Increasing the insulation resistance (RiтАЛ) reduces the leakage current component, which effectively improves the power factor of the cable towards unity by minimizing the ohmic losses associated with the insulation.
ILтАЛ=RiтАЛVтАЛ тАФ Leakage current through insulation resistance
cos╧Х=IR2тАЛ+IC2тАЛтАЛIRтАЛтАЛ тАФ Power factor expression for a leaky capacitor
An open-ended cable behaves like an R-C circuit where the capacitance (C) represents the dielectric medium and the insulation resistance (RiтАЛ) represents the path for leakage current. The total current is the phasor sum of the capacitive charging current and the resistive leakage current. By increasing RiтАЛ, the resistive current component decreases, reducing the loss angle and shifting the resultant current vector closer to the voltage vector, thereby improving the power factor.
Underground cables inherently possess capacitance due to the conductor-insulation-sheath geometry.
Leakage current flows through the insulation, which is inversely proportional to insulation resistance.
Power factor improvement in cables is synonymous with minimizing dielectric losses.
Higher insulation resistance implies better quality dielectric material.
Reduced dielectric power losses
Enhanced thermal stability of the cable
Higher cost of high-grade insulating materials
Finite limit to how much RiтАЛ can be increased physically
Underground transmission systems
High-voltage submarine cables
The power factor of a cable is often represented by the loss tangent, tan╬┤=ICтАЛIRтАЛтАЛ=╧ЙCRiтАЛ1тАЛ.
Option A is incorrect because increasing capacitance increases the reactive (capacitive) current, which worsens the power factor in leading systems.
D is correct тАФ Increasing the insulation resistance reduces the leakage current component, which brings the power factor closer to unity.
Always remember that in capacitive circuits, reducing the resistive component is a primary method for PF improvement, unlike inductive circuits where capacitors are added in parallel.