Neutral Current transformer

Neutral CT specification for power transformer when the CT is used in conjunction with Bias Differential Protection relay is insulation level 4KV or 6.6 KV,ratio :1500/1A 0r 1600/1A , Accuracy:class X,with Knee point voltage, ( for example ) = or > 150V depending on impedence of the line.No VA is specified.Class X because there is no accuracy class.1A secondary is to match the tripping coil's rated operating voltage.It may also be 5A depending on relay available to you.As this is normally custom made,you can order 1400/1A as well.15 MVA is a very common size.