# A 3- phase transformer bank is realized using three identical 1100/230 V, 10 kVA single-phase transformers connected in delta-delta, If one of the single-phase transformers develops a fault and is removed, the maximum load that the transformer bank in the open delta can supply is

A 3- phase transformer bank is realized using three identical 1100/230 V, 10 kVA single-phase transformers connected in delta-delta, If one of the single-phase transformers develops a fault and is removed, the maximum load that the transformer bank in the open delta can supply is

### Right Answer is: 17.32 kVA

#### SOLUTION

The capacity of the open delta system = √3 × rating of one transformer.

In an open delta or V-V transformer bank connection, only 86.6% or 0.866 rated capacity is available. This factor is also called a utility factor.

SVV = 0.866 × SDD

SVV = 0.866 × 20

SVV = 17.32 kVA

Important Points:

• An open delta connection of the 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, as their efficiency and overall rating is low when compared to delta-delta or closed delta systems which are used during standard operations.
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