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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.

Single Output HMT

WAVEFORMS Single output HMT has Special secondary interconnections construction designed by our electrical engineers produces a cancellation of the 3rd, 9th, 15th harmonics (triplets). we build a transformer with a Delta primary and a double interconnected winding secondary to cancel the triplen (zero sequence harmonics). Which will have:
• An adaptable transformer for non-linear loads
• A low-impedance cancellation of the 3rd, 9th, 15th harmonics
• A better equilibrium of phases and less harmonic voltage distortion (low-impedance Zero Sequence).

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Dual Output HMT

The HMT is equipped with dual 3-phase, 4-wire outputs. Each output has low zero phase sequence impedance which treats the triplen harmonics in much the same manner as the SINGLE OUTPUT HMT . In addition, there is a phase shift angle between the two outputs of 30° which cancels the balanced portion of 5th, 7th, 17th, and 19th current harmonic fluxes so that they are not coupled to the primary winding. This is equivalent to a 12 pulse rectifier where only residual amounts of these currents flow in the primary.

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Neutral Harmonics Eliminator

The Neutral Harmonics Eliminator is a parallel-connected, electromagnetic, zero sequence filter that removes 3rd and 9th harmonic currents as well as other zero sequence currents (Io) from the neutral conductor. The Neutral Harmonics eliminator presents a very low impedance alternate path for the neutral current to return to the phases because the windings of the NHE are configured to cancel the net flux created by the diverted neutral current. Neutral current, neutral-to-ground voltage, voltage distortion, and supply transformer losses are lowered because there is only a residual amount of 3rd harmonic and other zero sequence currents left in the neutral and phase conductors between the transformer and the NHE connection point.

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Features & Benefits


Eliminate circulating harmonic currents in primary windings of transformers.


Does electromagnetic flux harmonics cancellation; without filters, capacitors, or other devices.


Variety of phase-shift options available to treat specific harmonics in a system.


Low zero sequence impedance and zero sequence reactance.


Helps meet IEEET 519 harmonic limits.

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