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The insulation used in cable designed for┬а use on 1000 kV is usually
Impregnated paper
Compressed SF6тАЛ
PVC
Any of above
Compressed SF6тАЛ
For Ultra High Voltage (UHV) transmission levels like 1000 kV, conventional solid or liquid insulations face severe limitations due to dielectric losses and heat dissipation. Compressed Sulphur Hexafluoride (SF6тАЛ) gas is used in Gas-Insulated Transmission Lines (GIL) because it provides superior dielectric strength and excellent heat transfer capabilities under high-pressure conditions.
For Ultra High Voltage (UHV) transmission levels like 1000 kV, conventional solid or liquid insulations face severe limitations due to dielectric losses and heat dissipation. Compressed Sulphur Hexafluoride (SF6тАЛ) gas is used in Gas-Insulated Transmission Lines (GIL) because it provides superior dielectric strength and excellent heat transfer capabilities under high-pressure conditions.
EdтАЛтИЭP
dtd╧ХтАЛ=0
The dielectric strength of SF6тАЛ gas is approximately 2.5 to 3 times that of air at atmospheric pressure. By compressing the gas, its molecular density increases, significantly enhancing its ability to suppress electron avalanches and withstand the extreme electric field gradients present in 1000 kV systems.
SF6 is an electronegative gas with high electron attachment affinity.
GIL (Gas Insulated Line) systems are compact, allowing for reduced right-of-way requirements compared to overhead lines.
The dielectric strength of SF6 increases linearly with pressure P over a wide range.
High dielectric strength per unit pressure
Excellent arc quenching properties
Chemically inert and thermally stable
High cost of infrastructure
Gas leakage management
SF6 is a potent greenhouse gas requiring strict containment
Gas-Insulated Substations (GIS)
Ultra-High Voltage (UHV) transmission lines
Sub-sea power transmission cables
Impregnated paper is typically used up to 400 kV; above this, dielectric losses in cellulose become prohibitive.
PVC is unsuitable for HV applications due to high dielectric loss and poor corona resistance.
B is correct тАФ Compressed SF6тАЛ provides the necessary dielectric withstand capability for 1000 kV systems while minimizing cable size and dielectric losses.
Always remember that as system voltage increases into the UHV range, the shift from solid/liquid insulation to gaseous or vacuum-based insulation is driven primarily by the need to minimize dielectric tan-delta losses.