Will altitude of 3000 m be of any problem for insulated 11 kV ABC cable? Anyone has experience to share?

Hello, ampacity should be derated as per manufacturer's tables, or else calculated.

If the cables are laid such that their cooling is supposed to be due to air then cable capacity would drop because air is rarer at higher altitude. If, however, total length of cable is to be laid underground then there would no effect due to altitude. However, it must be borne in mind that there would in any case be some portion of cable laid in air. Out of this length, laid in air, the portion where outer sheath is removed shall not have much perceptible loss in capacity of the cable since the obstruction to heat flow due to the outer sheath is no longer present.

thank you for your valuable comments.. incase the cables without correction are laid? what would be the possible problem?

If the correction factors are not applied then there are chances of getting the cable overloaded, which will result in temperature rise and ultimately cable may fail to perform continually...! if the load is within the permissible limits of the cable conductor cross section, then nothing will happen and cable will perform normally...!

For medium voltage cable, distribution application, de-rating for altitude is not really necessary since temperatures are lower at that altitude and compensate for it.

Special care needs to be taken when jointing cable, some products used vaporise faster. Cable should be underground or in ducts or pipes. Protection from snow in winter and stronger UV-radiation at this altitude.
Temperature difference winter - summer should be checked, dilatation.

This is only valid for cables. Switchgear is different case or question!

Gerbrand R has offered a very good answer