Slashing Harmonics $aves

July 27, 2021

It is obvious how a variable frequency drive (VFD) saves energy and money by operating a motor at a reduced speed. Beyond just the reduction in power savings, VFDs with their inherent soft start and ramping can save in other ways such as equipment wear and tear. There is a new and exciting way VFD’s can impact building energy use beyond the piece of equipment it operates. It has to do with building electrical harmonics and how a building consumes electricity.

Electricity usage is different than other utilities used by a building. Water and natural gas consumption are directly measured. A given device that uses less of the resource to perform the desired output (i.e. more efficient) will cost the building owner less. An individual meter could be installed to determine the specific cost of operation.

With electrical loads, the manner in which a device draws its energy impacts the cost of operation along with the actual load. A buildings total system is comprised of linear and non-linear loads which results in a total building current (i.e. what the owner pays for).  This total current is made of fundamental current + harmonic current. The fundamental current is useful work being performed while the harmonic current is in effect the inefficiency of the system. More non-linear loads = more harmonics = LARGER utility bills. (NOTE: ABB has several technical articles that go into much greater detail if want to learn more)

VFDs get a lot of attention because they are large non-linear loads and responsible VFD manufacturers such as ABB have developed products and tools to predict and mitigate the harmonics they produce.   It is the latest product from ABB coupled with their harmonic calculators that allowed a large medical complex to improve their overall bottom line by using ABB Ultra Low Harmonic (ULH) variable frequency drive.

Initial calculations predicted an unacceptable amount of harmonics even with the ACH-580 industry-leading harmonic reduction features. The ABB harmonic calculation tools evaluated various options including harmonic traps, line reactors, and 18 pulse input units. Through this evaluation process, utilizing the ABB-580-ULH was found to reduce the VFD harmonic currents by a massive 285 Amps while meeting the buildings loads. This load reduction not only positively impacts energy costs, but also system areas like distribution transformer lifespan and sizing, and back-up generator operation.

If you have any curiosity about HOW the ULH saves this $$$$ beyond the motors it serves, we’d love to have that conversation with you. Contact the VFD group at Mulcahy to learn more about this game-changing product.

ABB Harmonic Calculator


Typical Harmonic Reduction Technique Comparison


Harmonic Calculation Key Results for a recent project


Initial Harmonic Evaluation


Ultra-Low Harmonic Evaluation


ULH Impact
284 Amp (83%) Reduction !
40% THD Reduction!



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