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Is there a 5% limit for the single phase loading on Delta-Delta connected Transformers with 240/120 Center Tapped secondaries?


Issue:
Center tap capacity of a center tapped delta secondary

Product Line:
LV Transformers

Environment:
Applies to Transformers with center tapped delta secondaries by SquareD/Schneider Electric

Cause:
Center tap capacity must be limited based on Transformer design factors

Resolution:

Delta-Delta connected Transformers are intended to supply balanced three-phase loads, such as motors and compressors. Unbalanced loading can cause a circulating current to flow in the windings. This additional current is like a ``hidden`` load with the Transformer windings and can severely de-rate or even overload the Transformer. Adding a Center Tap on the secondary for a combination of a 240V three-phase and 120V single-phase loads can exacerbate the effect in a more severe imbalance.  When applying 240/120V Secondary Three Phase Transformers by SquareD/Schneider Electric, such as those with catalog numbers ending in T6HCT, the amount of the imbalance allowed when using the Center Tap (CT) to feed 120V loads is limited to 5% of the overall rated KVA of the Transformer to help prevent excessive circulating currents. 

 

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