As far as I understand, the voltage which comes across the secondary wdg. of the CT should be less than the Vdesign.
Vdesign = ALF * VA * If/CTR
where,
ALF = Accuracy limit factor i.e, in case of a 10P10 CT ALF=10;
VA = Rated VA burden capacity of the CT;
If = Fault current;
CTR = CT Ratio
Now...
