For protection of inter-turn fault in transformer, the relays preferred are

• A. Buchholz's relay, overcurrent relay and differential relay
• B. Overcurrent relay and Buchholz's relay
• C. Buchholz's relay and differential relay
• D. Overcurrent relay and differential relay

Answer: (C)

Intern turn winding fault can be easily detect by differential protection relay.
Also detect by buchholz relay (gas operated relay), cause buchholz relay is used to detect the internal fault of transformer.