What is the difference between K-13 (Type NLP) and K-4 (Type NL) rated Transformers?

Issue:
Many loads used in Industrial and Commercial applications can generate harmonic energy which may be harmful to standard Transformers

Product Line:
LV Transformers

Environment:
Applies to Ventilated type Transformers by SquareD/Schneider Electric

Cause:
K rated Transformers are available as a possible solution to the problem of harmonic energy that might damage a standard Transformer

Resolution:

K-Factor is a measure of current distortion in the load fed by a Transformer. The higher the number, the greater the capacity of the Transformer to handle high levels of continuous single-phase, line-to-neutral non-linear loads. Square D/Schneider Electric recommends K-4 rated Transformers for computer and other similar loads found in commercial and industrial systems for duty cycles (24 hour average loading) of 80-95%. If the duty cycle is expected to exceed 95%, then K-13 would be needed. For duty cycles up to 50%, use Type EE energy efficient Transformers. For duty cycles of 50-80%, use Watchdog Low Temperature Rise Transformers.
The need for K-Factor rated Transformers is currently in question because standard, general purpose Transformers can supply typical commercial and industrial `non-linear` loads up to more than 80% of nameplate rating without overheating. Studies have shown that typical loading of low voltage dry Type transformers is less than 35% as a daily average.

Released for: Schneider Electric USA