11kV Voltage Grade

How about a telephone call to the cable supplier?

Quite simply the two values Uo/U relate to the cable's rated phase to neutral and phase to phase voltage.

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thank u very much... But in high voltage we dont have any neutral?

Then the first figure in the cable's insulation figures is not applicable to that particular installation.

I think you are confused between neutral & earth. Even ni an earlier posting of yours I had corrected you. System need not have a neutral but still can have a line earthed. If in a 3 phase, 3 wire system (without neutral as you said), if one of the phases gets earthed, what will be the voltage of the unfaulted lines with respect to earth? It would be the full line to line voltage. isn't it?

Now, imagine a 11kV, 3 phase, 3 wire armoured cable, without neutral. For safety reasons, the cable armour must be earthed. Now, if one of the phases gets shorted to earth, the cable armour would be raised to the potential of the grounded phase. The other two unfaulted phase cores of the cable will have a potential difference of full line voltage with this armour (whose potential now is that of the faulted phase). So, the insulation between the cable conductors & the earthed armour would be stressed to full line voltage. The insulation has to be designed accordingly. This is specified as 11kV (UE).

Alternately, if the same cable is used in an earthed neutral 11kV syatem, then such a cables earthed armour would always be at neutral potential and thus the cable conductors will always have a potential difference of about 6.35kV only with respect to earth or the earthed armour. Now, the cable insulation costs would reduce. This is specified as 11kV (E).

The reason for two values is because the rating specified as Earthed / Unearthed

22/22 means the cable is suitable for both 22kV earthed and unearthed system.