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Internal pressure cables has the advantage of
Elimination of external accessories
Suitability for vertical run without any fear of drainage with suitable design
Marked improvement in the power factor of cable dielectric with the increased pressure
All of above
Elimination of external accessories
Internal pressure cables, such as oil-filled or gas-pressure cables, utilize pressurized fluid or inert gas to maintain the dielectric insulation under stress. The positive pressure prevents the formation of voids and ionizable gas pockets, which are primary causes of dielectric breakdown in solid-type cables.
Internal pressure cables, such as oil-filled or gas-pressure cables, utilize pressurized fluid or inert gas to maintain the dielectric insulation under stress. The positive pressure prevents the formation of voids and ionizable gas pockets, which are primary causes of dielectric breakdown in solid-type cables.
EdтАЛтИЭP тАФ Dielectric strength is directly proportional to the applied pressure P in pressurized cable systems.
VstressтАЛ=rln(R/r)VтАЛ тАФ Maximum electrical stress at the conductor surface, which is managed effectively by pressure control.
In high-voltage cables, air bubbles or voids in the insulation act as weak points with lower dielectric strength. By maintaining the insulation (usually oil-impregnated paper) under high pressure, the dielectric strength is significantly improved (EbrтАЛтИЭP). The pressure also inhibits the migration of oil due to gravity in vertical runs and allows for a smaller overall cable diameter for a given voltage rating by enhancing the insulation efficiency.
Internal pressure maintains constant contact between insulating layers, eliminating air pockets.
Eliminates the 'void formation' phenomenon common in solid-type cables due to thermal expansion/contraction.
Allows operation at much higher voltage levels (e.g., 66kV to 500kV) compared to solid cables.
Pressure systems allow cables to be installed in vertical shafts without oil drainage issues.
High dielectric strength per unit thickness
Suitable for long-distance and vertical transmission
Self-monitoring of pressure leaks
Reduced likelihood of thermal runaway
Complex maintenance and installation
Requires pressurized reservoirs and auxiliary pumping equipment
High initial capital investment
Extra High Voltage (EHV) transmission (220kV and above)
Submarine power cable links
Deep vertical cable runs in high-rise structures or mine shafts
Oil-filled cables are generally subdivided into low-pressure (up to 3 bar) and high-pressure (up to 15 bar) systems.
Option A is correct because the self-contained design minimizes external support components compared to specialized gas-pipe systems.
Option B is correct because static oil pressure prevents migration, solving drainage problems in vertical installations.
D is correct тАФ Internal pressure cables provide void-free insulation, reliable vertical operation, and enhanced power factors through dielectric stress control.
Always remember that in cable engineering, dielectric reliability is limited by void formation; thus, any method increasing internal pressure directly increases the rated voltage capacity.