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The current carrying capacity of cables in DC is more than that in AC.┬а It is mainly due to
Smaller hysteresis losses
Absence of harmonics
Absence of ripples
None of above
Smaller hysteresis losses
The current carrying capacity of underground cables is significantly higher in DC compared to AC because DC cables do not suffer from Skin Effect, Proximity Effect, or dielectric losses (hysteresis and eddy currents) associated with oscillating magnetic fields. In AC, these phenomena effectively reduce the cross-sectional area available for current flow, thereby increasing resistance and limiting capacity.
The current carrying capacity of underground cables is significantly higher in DC compared to AC because DC cables do not suffer from Skin Effect, Proximity Effect, or dielectric losses (hysteresis and eddy currents) associated with oscillating magnetic fields. In AC, these phenomena effectively reduce the cross-sectional area available for current flow, thereby increasing resistance and limiting capacity.
RacтАЛ=RdcтАЛ(1+╬╗skinтАЛ) тАФ Relationship showing AC resistance increase
PdielectricтАЛ=V2╧ЙCtan(╬┤) тАФ Dielectric loss in AC cables
In AC cables, the magnetic flux linkage creates a non-uniform current distribution known as the Skin Effect, forcing current toward the surface of the conductor, which increases effective resistance RacтАЛ>RdcтАЛ. Additionally, the insulating dielectric material undergoes cyclic polarization, leading to energy loss in the form of heat, quantified as hysteresis and eddy current losses. Since DC maintains a constant voltage polarity, dielectric losses are negligible and the skin effect is absent, allowing for higher uniform current density.
DC cables are free from skin effect, resulting in uniform current density.
AC dielectric loss (hysteresis and eddy current) increases the heating of the cable.
Voltage stress is constant in DC, leading to better insulation utilization.
No proximity effect in DC circuits.
Higher power transmission capability for the same conductor size.
No charging current issues over long distances.
Requires expensive converter stations for AC-DC-AC conversion.
Switching and protection of high-voltage DC is more complex.
High Voltage Direct Current (HVDC) transmission lines.
Submarine cable links between grids.
Option B and C are incorrect because harmonics and ripples refer to quality of power supply, not the primary physical limitation of cable current carrying capacity due to impedance and material heating.
Hysteresis loss is specific to the dielectric under AC stress, contributing to internal cable heating which limits the maximum load current.
A is correct тАФ The higher current carrying capacity of DC cables compared to AC is primarily due to the absence of skin effect and negligible dielectric losses like hysteresis.
Always remember that 'Ampacity' (current carrying capacity) is limited by the heat a cable can dissipate; any effect that creates extra heat (like Skin Effect or dielectric loss) forces a derating of the conductor.