Parallel Connection of Transformers

Parallel connection of transformers is a common practice in electrical power systems. It allows for increased power capacity, redundancy, and flexibility in the system. However, not all types of transformers can be connected in parallel due to differences in their configurations and operating characteristics.

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 in industrial and distribution systems, where the load is typically balanced and ungrounded. The delta connection provides a higher degree of fault tolerance and allows for the use of three-phase and single-phase loads.

V-V Connected Transformer

A V-V connected transformer, also known as a Scott transformer, is a specialized transformer used to convert a three-phase system into two independent single-phase systems. It consists of two separate windings: a primary winding connected in a "V" configuration and a secondary winding connected in a "V" or "U" configuration. This type of connection is commonly used in applications where a balanced load is required in each single-phase system, such as railway traction systems.

Parallel Connection Limitations

When connecting transformers in parallel, it is essential to ensure that their configurations and operating characteristics are compatible. In the case of a V-V connected transformer, it cannot be directly connected in parallel to a delta-delta connected transformer. This limitation arises due to the following reasons:

1. Voltage Mismatch: The voltage ratios of a V-V connected transformer and a delta-delta connected transformer are different. The V-V transformer has a 1:1 voltage ratio, while the delta-delta transformer typically has a higher voltage ratio. Connecting transformers with different voltage ratios in parallel can result in unequal load sharing and potential damage to the transformers.

2. Phase Shift: The V-V connected transformer introduces a phase shift in the secondary voltage, which is not present in a delta-delta connected transformer. This phase shift can cause issues when connected in parallel, as the transformers may not operate in synchronism and can lead to circulating currents and excessive heating.

Alternative Connections

While a V-V connected transformer cannot be directly connected in parallel to a delta-delta connected transformer, it can be connected in parallel to other compatible transformer configurations, such as:

- Star-Delta Connected Transformer (Option B): This connection allows for the conversion between a three-phase system and a single-phase system. It is commonly used in industrial applications where a balanced load is required in the single-phase system.

- Star-V Connected Transformer (Option C): This connection is similar to the V-V connected transformer but with a star configuration on the primary side. It is mainly used in systems where unbalanced loads are present in the single-phase system.

- All of the Mentioned (Option D): This option is incorrect because a V-V connected transformer cannot be connected in parallel to a delta-delta connected transformer, as explained above.

Therefore, the correct answer is option A: Delta-Star connected transformer.