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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. Unbalanced loading will 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 will exacerbate the effect in a more severe imbalance.  In older design Transformers by SquareD/Schneider Electric, such as those with catalog numbers ending in T6HCT, the amount of the imbalance was limited to 5% to help prevent excessive circulating currents.  Newer designs, such as the EE75T151HCT, have a much higher, 30% limit to loading on the center tap.  See below attachment for more details. 


CTA-ID : 2001190

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