Why all 415V transformers are chosen Dyn 11? What are the protections provided for the 415V transformers?

Why all 415V transformers are chosen Dyn 11? What are the protections provided for the 415V transformers?
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1 Answer

Answer :

a) To facilitate interchange.

b) To have momentary parallel during changeover.

Protections

a) Door interlock to trip HT and LT breakers.

b) LT breaker can on only after HT breaker is in on position.

c) Instantaneous O/C and inverse O/C (50 + 51).

d) Instantaneous E/F (50N).

e) IDMT E/F and restricted E/F (51N + 64).

f) Winding temp high trip (140°C trip and 130°C alarm) 
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