Rockwell Automation 1404-M4_M5_M6_M8 Powermonitor 3000 User Manual, Firmware rev. 3.0 or LATER - Manual (Page 169)

Publication 1404-UM001F-EN-P - November 2009 169
Advanced Features Chapter 8
K-Factor
K-Factor measures additional heating in a power transformer due to
the harmonics in the power signal. These harmonics cause additional
heating due to increased core losses that occur at higher frequencies.
The increased losses are related to the square of the harmonic
frequency. Therefore, a slight harmonic content can significantly
increase the heat rise in a power transformer. The additional harmonic
heating may cause a transformer to exceed designed temperature
limits even though the RMS current is less than the transformer rating.
The K-Factor is used as justification to oversize a power transformer to
allow extra margin for harmonic losses or to select an appropriate
K-Factor rated transformer. A K-Factor rated transformer is the
preferred choice since it has known performance in the presence of
harmonics. The formula for K-Factor is as follows:
K-Factor
∞
Σ
n 1 =
Hn
2
n
2
•
⎝ ⎠
⎛ ⎞
∞
Σ
n 1 =
Hn ( )
2
----------------------------------------- =
Where:
•
H
n
= magnitude of the n
th
harmonic (n
≤
41 or 63).