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Draft:K-factor (electrical engineering)

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In electrical engineering, the K-factor of a power transformer is a measure of how well it can handle harmonic distortion. Transformers which are designed to handle harmonic distortion are referred to as K-rated transformers.[1][2][3]

Background

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In an alternating current power system, electrical energy is ideally transmitted as a pure sine wave, typically at a fundamental frequency of 50 Hz or 60 Hz. However, distortion in the power system can result in a non-sinusoidal waveform. This deviation from a pure sinusoidal waveform is measured using harmonics. The nth harmonic is a waveform at an integer multiple of the fundamental frequency. For example, a wave transmitted with a fundamental frequency of 60 Hz would have its 2nd harmonic at 120 Hz, its 3rd harmonic at 180 Hz, its 4th harmonic at 240 Hz, and so on.[4]

Calculation

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The following formula is used to calculate the K-factor of a transformer:[5]

Where:

  • K is the K-factor
  • h is the harmonic order
  • Ih is the per-unit current at the hth harmonic order

Typical Values

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The following table lists typical K-factors used depending on the harmonics produced by the loads:[5]

Typical K-factors
K-factor Load description Harmonic activity
1 Standard, general-purpose transformer <15% of loads generate harmonics
4 Induction heating, AC drives Up to 35% of loads generate harmonics
13 Institutional electronically controlled lighting 35-75% of loads generate harmonics
20 Data processing equipment, computer servers 60-100% of loads generate harmonics
30-50 Loads consistently generate harmonics 100% of loads generate harmonics

Transformers with a larger K-factor are more expensive

References

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