Correct Answer - Option 3 :

\(100:\frac{5}{{\sqrt 3 }}\)
The line current on the star side of the power transformer will be

\(500 \times \frac{{6.6}}{{33}} = 100\ amps\)

The CTs on the star side are delta connected and the current required on the relay side of the CT is 5 amps. Therefore, the current in the CT secondary is 5/√3. The CT ratio of the HV side will be

\(\begin{array}{l} 100:5/\sqrt 3 \\ = 20\sqrt 3 :1 \end{array}\)