Under Ground Cabling

I know this is covered in the electrical specifications somewhere for the area in which you are concerned. It may vary from one locality to the next.

It also depends on how much current that 1100V cable is carrying because it is current that will determine the magnetic field that you are worried about. Shielded communication cable should be useful in defending against unwanted coupling but distance from the AC power line is also helpful. Your success may also depend on the communication circuit used. Some methods reject common mode noise better than others.

If both cables are running in the same path, you will want to maximize distance and shielding or you may end up running the communication cable again.

Even if we are using armoured MV cables and Optical fibre communication cable also,

will we have magnetic Interferences?

Optical fiber communications will not be affected in any appreciable way by the electro-magnetic fields of an MV cable, and can be put in the same ducts or enclosures. Your main consideration then is minimum approach distances and the safety of personnel if you need to work on the fibers when the MV is energized.

But you should check your local codes - they may say you cannot in any case.

NESC [C2-2007] Rule 353:

Minimum radial separation between any cable and other should be 300 mm [12 inches].

However, radial separation should be adequate to permit access to and maintenance of either facility to limit damage to the other.

For fiber-optic communication cable this clearance can be less- see NESC Rule 354 D.