T&D World Magazine

Harmonic Mitigating Transformers Prevent Harmonic Damage

Harmonics can overheat electrical systems, causing less capacity, more noise and shortened lives for transformers. Guard III Harmonic Mitigating Transformers from GE Consumer & Industrial curb harmonic currents that K-factor transformers do not, reduce transformer heating caused by harmonics and improve upstream power quality, all while maintaining the NEMA TP-1 standard for energy efficiency.

"Harmonics are everywhere," says Bill Forsythe, product manager, GE Consumer & Industrial. "Unlike K-factor transformers, which merely reduce transformer heating due to poor power quality, Guard III transformers from GE help to improve power quality, extend transformer life and reduce premature transformer failure."

The Guard III Harmonic Mitigating Transformers, which accomplish harmonic mitigation by providing good source impedance and sine wave phase shifting, round out GE's line of power quality product offerings. A Guard I transformer is any GE transformer, other than a K-factor transformer, that incorporates an electrostatic shield. A Guard II transformer incorporates the same electrostatic shield as the Guard I, while featuring components to enhance spike and surge suppression. Guard I, II and III are selected based on the type of building or installation.

Harmonic mitigating transformers (HMTs) come in specific phase shifts of 0, 15, 30 and 45°. Using a drive installation as an example, phase shifting transformers are useful for configurations where multiple drives can be placed into tow, or 4 groups where the total drive power within each group is about the same. By using 2 groups of drives, 1 group on a 0° phase shift, and the other on a 30° phase shift, it's possible to cancel most of the 5th and 7th harmonics, mimicking a 12-pulse system. The same is true with 15° and 45° phase shift transformers. With 4 groups of drives, placing a group onto each of the four phase shifts will cancel most of the 5th, 7th, 11th and 13th harmonics, mimicking an 18-pulse system. If some of the drives were stopped, there would be less cancellation. The worst-case condition for voltage distortion is when all of the drives are at full load.

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