When a three-phase load is comparatively small so that the installation does not warrant a 3-transformer bank. Which of the following 3-phase transformer connection is used?

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DFCCIL Executive Electrical 2016 Official Paper
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  1. V - V connection
  2. Delta-star connection
  3. T - T Scott connection
  4. Y - Y connection

Answer (Detailed Solution Below)

Option 1 : V - V connection
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Detailed Solution

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Open-delta connection:

  • An open delta connection transformer uses two single-phase transformers to provide a three-phase supply to the load.
  • An open delta connection system is also called a V-V system.
  • Open delta connection systems are usually only used in emergency conditions when one of the transformers in the Delta-Delta system is damaged, and removed from service.    
  • Efficiency for the operation of open delta connection is low as compared to delta-delta systems which are used during standard operations.
  • When the three-phase load is comparatively small so that the installation does not warrant a 3-transformer bank. Then open delta connection is also used.


Power supplied by open delta connection

Power supplied by open delta connection

Therefore, 

Hence, the total load supplied by the open delta system is 57.77% of the closed delta system.

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