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Humidity repellent compound used in which distribution system?
Overhead
Underground
Outdoor
None of this
Underground
Humidity repellent compounds (like bitumen or specialized resins) are used in underground distribution systems to prevent moisture ingress into cable insulation. Moisture penetration can lead to the degradation of dielectric strength, partial discharge, and eventual insulation failure of underground cables.
Humidity repellent compounds (like bitumen or specialized resins) are used in underground distribution systems to prevent moisture ingress into cable insulation. Moisture penetration can lead to the degradation of dielectric strength, partial discharge, and eventual insulation failure of underground cables.
R=╧БAlтАЛ тАФ Where R is insulation resistance, influenced by the dielectric medium status
IleakтАЛ=RinsтАЛVтАЛ тАФ Leakage current increases significantly if moisture enters the cable dielectric
Underground cables are laid in trenches or ducts where they are exposed to groundwater and soil moisture. Humidity repellent compounds act as hydrophobic barriers within the cable's sheath and jointing materials to maintain high insulation resistance (RinsтАЛ) and prevent oxidation of metallic armor and conductors. This is critical because underground environments lack the natural air-drying mechanism present in overhead lines.
Underground cables utilize multi-layer construction including bedding, armor, and serving.
Bituminous compounds are used in cable boxes and joints as a water-sealing agent.
Moisture in cable insulation significantly increases the loss tangent (tan╬┤).
Prevents electrolytic corrosion of metallic sheaths.
Maintains consistent dielectric properties over time.
Protects against insulation breakdown due to water absorption.
Compounds can become brittle at very low temperatures.
Difficult to remove during cable maintenance or joint repairs.
Cable jointing and termination kits.
Underground cable trenching and duct sealing.
Sealing of cable entry points into substations.
| Feature | Overhead | Underground |
|---|---|---|
Environment | Exposed to atmospheric moisture | Exposed to groundwater/soil |
Protection Needed | Corona/Lightning/Wind | Moisture ingress/Corrosion |
Humidity repellent compounds are technically referred to as potting compounds or filling compounds in cable engineering.
Overhead lines do not require these compounds because atmospheric air serves as the insulator, and rain naturally drains off conductors.
B is correct тАФ Humidity repellent compounds are specifically required in underground systems to protect insulation from moisture-induced dielectric degradation.
In competitive exams, remember that underground cables are designed with the 'three-fold' defense: mechanical armor, moisture-proof sheath, and insulation-repellent filling.