When a non-linear load (LED driver, VFD, IT, EV charger) draws current with harmonics, the transformer feeding it suffers extra eddy-current losses. A standard K-1 transformer overheats at well below rated load. K-factor transformers are designed for harmonic heat, and Saudi modern buildings need them.
Four ideas to carry into the next specification conversation you have.
K-1 = pure sinusoidal load. K-4 = mild harmonic. K-13 = typical IT/LED building. K-20 = data centre / heavy non-linear.
Each harmonic causes losses proportional to its squared frequency × squared current. The 5th harmonic at 10% current causes 25× the loss factor of the same current at fundamental.
3rd, 9th, 15th harmonics from single-phase loads (LED, IT power supplies) circulate in the transformer's delta winding, causing extra copper loss without doing useful work.
Cannot retrofit. The transformer's iron and copper construction differ: larger neutral conductor, special core lamination, oversized windings. Choose the K-rating up-front.
Per UL 1561 / IEEE C57.110.
| K rating | Load type | Saudi application |
|---|---|---|
| K-1 | Pure linear (resistive heaters, lights) | Legacy industrial, no LED |
| K-4 | Mild harmonics (some VFDs) | Small workshop |
| K-9 | Moderate harmonics | Mid-size office, LED + some IT |
| K-13 | Heavy harmonics | Modern Saudi office / retail (default) |
| K-20 | Very heavy non-linear | Data centre, IT-heavy floor |
| K-30 | Extreme non-linear | VFD-heavy industrial, EV charger banks |
| K-40 | Worst case | Specialty applications |
Five points the consultant must get right at design.
K-factor is calculated from the actual load's harmonic profile. K = Σ (Ih/I)² × h² across all harmonics. For new buildings without measured data, use IEEE C57.110 typical profiles by load type.
Triplen harmonics from single-phase non-linear loads (LED drivers, computer PSUs) sum in the neutral instead of cancelling. A standard 100% neutral overheats in a K-13 installation. Spec 200% neutral as default.
A K-1 transformer in a K-13 building must be de-rated 30-40% to survive the harmonic heat. You pay for a 1000 kVA transformer to deliver 700 kVA. Buying K-13 from start is cheaper per delivered kVA.
Several smaller K-13 transformers serving zones beat one giant K-20 serving the whole building, better fault isolation, less harmonic mixing, easier maintenance. Match K-rating to each zone's load profile.
Dry-type (cast resin, K-rated) is the Saudi indoor default, no oil, low fire load, easy maintenance. Liquid-filled (mineral oil) for outdoor MV; ester oil for newer eco-spec projects. Both can be K-rated.
Our distribution transformers ship K-13 standard for Saudi commercial. Dry-type with cast resin for indoor, oil-filled for outdoor MV. 200% rated neutral on every K-rated unit.
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