Are electrical systems safe from harmonics if K Rated transformers?
K-Rated transformers made their appearance several decades ago as a means of preventing transformers from failing when subjected to heavy non-linear loading. They are essentially ‘beefed up’ transformers with extra steel in their cores and conductors in their windings to allow for better dissipation of the excessive losses produced by harmonic currents. K-Rated transformers are not designed to cancel harmonics so they do nothing to reduce harmonic distortion in a power system.
When the non-linear loads are single phase such as switch-mode power supplies, significant levels of triplen (3rd and 9th) harmonics are created which can cause excessive loading in the neutral conductor. K-rated transformers have a larger neutral conductor to accommodate for triplen harmonics. Triplen harmonic currents can be reduced by the use of Harmonic Mitigating Transformers. When the non-linear loads are three phase in nature such as variable frequency drives, harmonic currents can be reduced by the use of passive harmonic filters, active harmonic filters or phase shifting transformers.