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Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
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Cables used for 220 kV lines are invariably
Compressed oil or compressed gas insulated
Paper insulated
Mica insulated
None of above
Compressed oil or compressed gas insulated
Cables designed for Extra High Voltage (EHV) levels like 220 kV require advanced insulation systems to minimize dielectric losses and prevent internal ionization. Compressed oil or compressed gas insulation systems are used because they maintain high dielectric strength and effectively dissipate heat generated by the cable under load.
Cables designed for Extra High Voltage (EHV) levels like 220 kV require advanced insulation systems to minimize dielectric losses and prevent internal ionization. Compressed oil or compressed gas insulation systems are used because they maintain high dielectric strength and effectively dissipate heat generated by the cable under load.
E=rln(R/r)VтАЛ тАФ Electric field stress at the conductor surface in a single-core cable
In oil-filled cables, the dielectric (typically paper) is impregnated with low-viscosity oil maintained at high pressure, which prevents voids from forming and ensures that any breakdown of insulation is suppressed. In gas-pressurized cables (like SF6тАЛ), the high-pressure gas acts as both the dielectric medium and a superior coolant, significantly reducing the cable's physical dimensions and weight compared to solid-insulated alternatives.
Solid insulation is prone to ionization voids at voltages above 66 kV.
Pressure systems (oil/gas) ensure the insulation remains gap-free.
Higher pressure increases the dielectric breakdown strength of the insulation.
220 kV systems require sophisticated sheath bonding to reduce circulating currents.
Elimination of internal voids in insulation
Superior heat transfer capabilities
Reduced insulation thickness
High dielectric integrity
High maintenance complexity
Risk of leakage of oil/gas
Requires auxiliary pressure maintaining equipment
Underground transmission networks
Submarine power interconnections
HVDC link terminations
Paper insulation alone is insufficient for 220 kV due to the likelihood of partial discharge occurring in air pockets within the insulation layers.
Option B (Paper insulated) refers to solid-type impregnated paper, which is generally limited to voltages up to 33 kV or 66 kV.
A is correct тАФ 220 kV cables require pressurized fluid or gas insulation to eliminate dielectric voids and manage heat.
Always remember that as voltage increases beyond 66 kV, the focus in cable design shifts from dielectric strength of materials to the suppression of internal ionization (voids).