EMA Inc.

Harmonics, how do they affect your equipment?

Like many of you, until recent years I was unaware of the effects of harmonic currents on electronics, motors, and motor drives. Most of the time, plant and facility engineers are unaware that they have harmonic issues until they begin experiencing inexplicable circuit breaker trips or line fuses opening. These symptoms could be a manifestation of serous harmonic issues. Harmonic currents, are useless integer multiples of the fundamental line frequency. These are often induced by non-linear loads.

You can see the effects of harmonics in the image on the left. The Green useful current is a 60 HZ sine wave, free of harmonics. The Red current is useless harmonic current, and the White current is the algebraic sum of the useful and useless currents. The White current is a typical representation of what harmonic distortion looks like.

Harmonics can be classified into positive, negative, and zero sequences. The positive harmonic sequence attempts to force electric motors to run faster than the applied stator frequency. This causes heating and loss of torque. The negative harmonic sequence attempts to force the motor to run slower than the applied frequency, and zero sequences result in a higher current flow through the neutral conductor.

A similar result occurs when harmonics are imposed on VFDs and other electronics. The electronic circuits are designed to operate on the fundamental frequency (60 HZ in the United States) yet due to harmonic distortion, are subjected to additional heating and wasted energy.

Cleaning harmonics from your power system results in higher efficiencies, and longer life on all electrical conductors. This would include motors, transformers, cables, VFDs, and other electronics.

Is your system subject to harmonic distortion? Let EMA help you investigate this. EMA has a partnership with Schaffner Harmonic Filters, and a great deal of experience in mitigating harmonic issues. Call us, we can help. Call your nearest EMA Facility, phone numbers are at the bottom of this page, OR, just click “Contact Us” in the top right.

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