The thermal resistance depends on the geometry of the cable and the thermal resistance ‘K’ of the insulate. For a single core cable the thermal resistance between the conductor of radius ‘r’ and sheath of overall radius ‘R’ is proportional to the thermal resistivity “K” and thickness of the cable insulates, and inversely proportional to the surface area of the sheath. It can be expressed as R_th = K/2π 〖log〗_e R/r °C/watt . For a 1 cm length of cable (i.e. thermal ohms/cm).

1. What is called “Barrier joint” of cable ?
2. Interview Question of Underground Cable
3. What are varnished cambric insulated cables ?
4. What do you mean by XLPE cable and what are its advantages over conventional cables ?
5. What do you mean by MIND cable and where is it used ?
6. What do you mean by the term “Sheath losses” ?
7. What is the procedure of reducing the sheath losses in sheaths of the three single core cables in a 3-phase system ?
8. What do you mean by the term “Dielectric losses” ?
9. What do you mean by thermal resistance of a single core cable ?
10. What are the load conditions of an underground cable ?
11. what special cares are to be taken for storage of cable drum ?
12. What are the methods of cable laying ?
13. What is soil thermal resistivity ?
14. What is proximity effect ?
15. What are the procedures to be adopted for determining the types of cable faults ?
16. What precaution should be taken while taken a cable through trenches in the following locations (a) Road crossing, (b) Railway crossing & (c) Crossing of water mains ?
17. What is called “Heat shrinkable joint” of cable?
18. What can be the causes of damage to PVC cables and paper insulated cables?