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Star-star power transformer is protected by current transformer having
1. Star/star connections
2. Delta/delta connections
3. Star/delta connections
4. Delta/star connections

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Correct Answer - Option 2 : Delta/delta connections

Merz-price differential protection scheme:

  • Merz-price differential protection is nothing but a percentage differential protection.
  • It works under the principle of the circulating current scheme.
  • Merz-price differential protection is used to protect the transformer from internal short circuits, Internal ground faults, and inter-turn short circuits.


The CTs connection in the Merz-price protection:

CTs are connected to every phase of the system.

In order to nullify the phase shift of the Power transformer (PT), The Current transformers (CT) connected in a reverse configuration.

Configuration of PT

Configuration of CTs on primary and secondary of PT respectively

Y – Y

∆ - ∆

Y - ∆

∆ - Y

∆ - Y

Y - ∆

∆ - ∆

Y - Y

The star-star power transformer is protected by the current transformer having delta/delta connections.

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