Sunday, October 12, 2014

Comparison between Three Phase Overhead and Underground cables

Power can be transferred through Overhead cables or Underground cables. In overhead lines inductance is predominant and in case of underground cables capacitance is predominant.

There are always advantages of Overhead transmission lines in comparison to underground cables:-

1.     The conductor used in Overhead transmission lines is less expensive as size of cable required in overhead lines is less than underground cables. As overhead lines have better heat dissipation than underground cables.

2.     Insulation cost in case of underground cables is more than overhead lines. Overhead lines use bare conductors which are well supported and provide sufficient spacing between conductors. But in underground cables insulation is provided by various high grade paper tapes. A metal sheath is also provided so that moisture doesn’t enter the cable. Oil and inert gas is inserted so as to fill voids. Also storage vessels are needed to be installed after some intervals so to makeup the voids created during expansion and contraction of oil or gas in cables.
3.     Also erection cost of overhead line is much less than underground cables.
4.     It is easy to do capacity addition in overhead lines than underground cables.

There is some advantages of underground transmission than overhead transmission:-\

1. Underground cables provide safety to public.
2. Underground cable doesn't give interference and also underground cables provide better looks to surroundings.