This Article is about the differences between K-Factor vs Factor K.

The K Factor is easy formula, more harmonics more K to derate transformer, only needs Amp waveform to calculate harmonics.

Factor K is similar but different formula standardized in 2 EN standards see below. 


EN 50464-3:2007
Three-phase oil-immersed distribution transformers 50 Hz, from 50 kVA to 2 500 kVA with highest voltage for equipment not exceeding 36 kV - Part 3: Determination of the power rating of a transformer loaded with non-sinusoidal currents
English: https://standards.globalspec.com/std/1037406/EN%2050464-3
Or German: https://www.beuth.de/en/standard/din-en-50464-3/102533948

EN 50541-2:2014
Three phase dry-type distribution transformers 50 Hz, from 100 kVA to 3 150 kVA, with highest voltage for equipment not exceeding 36 kV - Part 2: Determination of load ability of a transformer loaded with non-sinusoidal current
English: https://standards.globalspec.com/std/9877637/cei-en-50541-2
German: https://www.beuth.de/en/erweiterte-suche/272130!search?alx.searchType=complex&searchAreaId=1&query=EN+50541-2&facets%5B276624%5D=&hitsPerPage=10

It is used to de-rate distribution (Medium Voltage to Low Voltage) transformers by utilities DNO’s.
Formula is more complex EN uses factors specific for each transformer supplied by manufacturer.