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.