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As our world becomes more dependent on electrical and electronic equipment, there is an increased likelihood that operations will experience the negative effects: increased harmonic distortion in the electrical distribution system. The difficult thing about harmonic distortion is determining the source. Once this task has been completed, the solution can be easy. Harmonic mitigating transformers (HMTs) are one of the many possible solutions to help eliminate these harmful harmonics.

HMTs are an economical solution in the battle against the harmful effects of harmonics. Harmonic Mitigating Transformers are specially designed to reduce system voltage distortion in addition to reducing the heating effects caused by the harmonic currents. This is accomplished by canceling load generated harmonic fluxes and currents within the transformers windings.

Harmonic mitigating transformers are commonly referred to as “phase-shifting” transformers. The HMT offering from Eaton’s electrical business has delta-connected primary windings and wye zig-zag connected secondary windings. The use of wye zig-zag secondary windings allows a transformer to be designed in a wide variety of different phase-shifts (–30°, –15°, 0°, +15°). In standard delta-wye transformers, including K-factor–rated transformers, triplen harmonics are passed from the secondary windings into the primary delta windings, where they are trapped and circulate. In HMTs, the electromagnetic flux cancellation created by the wye zig-zag winding configuration prevents 3rd and other triplen harmonics from being transmitted into the primary delta winding. Harmonic treatment is provided entirely by electromagnetic flux cancellation; no filters, capacitors or other such devices are used. It is important to remember that the harmonic currents still flow in the secondary windings.

Harmonic Mitigating Transformers significantly outperform their normal conventional transformer. Power distribution systems designed with HMT’s are capable of servicing any level of non-linear loading without suffering negative consequences. This should justify more widespread use of the HMT in applications where high concentrations of non-linear loads are found.