Are SquareD/Schneider Electric Drive Isolation Transformers K-Rated? Do they need to be?

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Issue:
Differentiation between K4/K13 and HDIT type Transformers

Product Line:
LV Transformers

Environment:
Applies to K4 and K13 and Drive Isolation Transformers by SquareD/Schneider Electric

Cause:
Special Transformers are available for both Non Linear (K4 and K13) and Drive Isolation applications

Resolution:

No to both questions. The UL K-Factor test evaluates temperature rise only. That is satisfactory for relatively passive applications such as computers and other office equipment loads. Drive Isolation Transformers are subjected to much more severe mechanical stress and thermal and mechanical cycling effects than K-rated Transformers. In addition, a motor drive`s K-Factor depends on the reactance of the line to which it is connected. In other words, the Transformer and the system, not the motor drive, determines the K-Factor. Therefore, choosing a universally appropriate K-Factor rating for a drive isolation Transformer is impossible. Most importantly, most K-Factor rated Transformers have insufficient reactance for proper drive harmonic control.