The sheath loss of a cable is a power loss occurs in the lead sheath as a result of the induced e.m.f. produced by the flux linkage with the lead sheath. When single core paper insulated lead covered and served power cables are used on a.c. system the presence of a lead sheath around each insulated conductor has an important effect on the electrical characteristics and current rating of the cable. If the lead sheaths are bonded together or earthed a voltage will be induced in the open circuited sheaths by transformer action between the conductors and the sheaths, the value of which depends on the flux interlinked with the lead sheaths and increases with the increase in the interaxial spacing of the cables. The induced sheath voltages are short circuited through the bonding resulting a flow of current along the sheath and thus dissipating energy as heat through the cable serving and surrounding earth or air. The eddy currents are also generated in the lead sheaths due to the lack of perfect symmetry in the lead sheath circuit relative to the magnetic field. Therefore the heating losses which occur in the lead sheaths are of two types e.g. (a) sheath circuit loss for bonded sheaths only and (b) sheath eddy loss. The sheath eddy loss is generally very small compared with the sheath circuit loss and can be neglected in many cases.

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?