The 33/11 kV delta–star transformer and CT connections are shown. Both-side CT ratios are 500/5. For the indicated 300 A fault, the currents i1 and i2 are
The per-winding HV/LV turns ratio is 33000/(11000/√3)=3√3. A 300 A current in the faulted LV winding is therefore balanced by 300/(3√3)=100/√3 A in the associated delta winding.
The indicated HV-side CT lead consequently carries (100/√3)/100=1/√3 A, using the 500/5=100 ratio. The indicated LV CT lead i2 belongs to the unfaulted phase path in the drawing and carries zero for this single-phase fault.
Thus the pair is **1/√3 A and 0 A, A**. Current directions and the specific lead labels follow the supplied CT connection diagram.
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