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How do you calculate the required transformer capacity (in kVA) rating for a 3 phase transformer?

Issue:
Calculation of KVA capacity for a Three Phase Transformer, based on Winding Voltage and Amperage information.
 
Product Line:
LV Transformers
 
Environment:
Applies to all Three Phase Transformers.
 
Cause:
KVA sizing must often be calculated from Primary or Secondary Winding Voltage and Amperage information.
 
Resolution:

To do this you must have at least two pieces of information:  1) the load line-to-line voltage (V), and 2) the maximum load phase current (I).

kVA = (V * I * 1.732) / 1000
where 1.732 is the simple numerical value for the square root of 3 (1.7320508...)

Then round up to the next standard 3ph kVA rating as found in Section 14 of SquareD/Schneider Electric Catalog, Digest 176.

Example:  V = 208, I = 175; this calculates to 63+ kVA, thus we round up to 75kVA.  From the Digest, a EE75T3H will satisfactorily serve this load.

Note:  This is a simple kVA calculation and does not take into account possible special load requirements, such as found with motors or some medical equipment.  For assistance, contact Product Marketing for support.


Example:  For this, V = 208 (the load line-to-line voltage); I = 175 (175 amps per phase conductor)

kVA = (208 * 175 1.732) / 1000 = 63..05kVA   Thus, round up to a 75kVA transformer.  In this example, an EE75T3H.


FA101694  |  30-Oct-2013  | Selection
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