For the protection of a delta-star transfomer using differential protection scheme, which of the following CT connection is used?

Correct option is C

The connection of current transformer (CT) is opposite to the connection of power transformer like –

​$$\begin{array}{|c|c|}\hline\textbf{Power transformer} & \textbf{Current transformer} \\\hline\text{Star – Star} & \text{Delta - Delta} \\\text{Delta – Delta} & \text{Star - Star} \\\text{Star - Delta} & \text{Delta - Star} \\\text{Delta - Star} & \text{Star - Delta} \\\hline\end{array}$$​​