K-factor (electrical engineering)
{{Short description|Measure of a transformer's ability to withstand harmonic distortion}}
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.{{cite web|url=https://canadatransformers.com/k-factor|archive-url=https://web.archive.org/web/20141031121016/http://www.canadatransformers.com/k-factor/|archive-date=2014-10-31|title=K-Factor rated transforemer for deal with harmonic generating loads|website=Canada Transformers}}{{cite web|url=https://www.electricalclassroom.com/k-factor-rated-transformers/|title=What are K-factor rated transformers?|website=Electrical Classroom|date=11 October 2020 }}{{cite web|url=https://www.rexpowermagnetics.com/products/dry-type-low-voltage-transformers/k-rated-transformers|archive-url=https://web.archive.org/web/20240301055810/https://www.rexpowermagnetics.com/products/dry-type-low-voltage-transformers/k-rated-transformers|archive-date=2024-03-01|title=K-Factor Rated Transformers|website=Rex Power Magnetics}}
Harmonics
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, switching can lead to distortion in the power system, resulting in a non-sinusoidal waveform. This deviation from a pure sinusoidal waveform is measured using harmonics. The {{math|n}}th 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. The waveform is considered to be a sum of all harmonic components.{{cite web|url=https://www.maddox.com/resources/articles/guide-to-transformer-harmonics-and-k-factor|title=Guide to Transformer Harmonics and K-factor|website=Maddox}} A K-rated power transformer is one that is designed to withstand this harmonic distortion. The K-factor is a measure of how well it mitigates distortion.
Calculation
The following formula is used to calculate the K-factor of a transformer:{{Cite web|first=Frank|last=Basciano|title=What is a transformer K-factor rating?|url=https://library.e.abb.com/public/53968e937e084cfea172fa33adb40ac2/20230429_ABB_1TQC194900E0001_K-factor%20ELSB%20LVDTT%20Tech%20Paper.pdf|publisher=ABB|date=2023-04-29}}
:
Where:
- {{math|K}} is the K-factor
- {{math|h}} is the harmonic order
- {{math|Ih}} is the per-unit current at the {{math|h}}th harmonic order
Typical Values
The following table lists typical K-factors used depending on the harmonics produced by the loads:
| class="wikitable"
|+ 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 to produce.