Parallel Connection of Transformers
In electrical engineering, transformers can be connected in parallel to increase the overall power capacity and reliability of the system. However, there are certain restrictions on how transformers can be connected in parallel based on their configurations.

Delta-Delta Connected Transformer
A delta-delta connected transformer has its primary and secondary windings connected in a delta configuration. This type of connection is commonly used for industrial applications where high fault tolerance and low impedance are required.

Delta-Star Connected Transformer
A delta-star connected transformer has its primary winding connected in a delta configuration and the secondary winding connected in a star (wye) configuration. This type of connection is commonly used for distribution systems where the neutral point is required for grounding.

Star-Delta Connected Transformer
A star-delta connected transformer has its primary winding connected in a star (wye) configuration and the secondary winding connected in a delta configuration. This type of connection is commonly used for applications where a high voltage is required on the primary side.

Star-V Connected Transformer
A star-V connected transformer has its primary winding connected in a star (wye) configuration and the secondary winding connected in a V configuration. This type of connection is not commonly used and is not a standard transformer connection.

Incompatibility with Delta-Star Connection
When connecting transformers in parallel, it is important to ensure that the configurations of the transformers are compatible. In the case of a V-V connected transformer, it cannot be connected in parallel to a delta-star connected transformer due to the mismatch in their winding configurations.
Therefore, the correct answer is option 'A' - a V-V connected transformer can be connected in parallel to a delta-delta connected transformer but not to a delta-star connected transformer.