Variable Frequency Drives & Digital Phase Converters

Low Harmonics

Why Low Harmonics Are Important

Phase Technologies’ LH Series drives use a state of the art active switching input module to limit harmonic distortion of the input current, therefore limiting voltage harmonics on the power system.

The benefits of choosing LH Series drives include:

  • Less expensive smaller transformers in the utility service
  • Lower utility bills
  • Improved reliability
  • Lower maintenance costs
  • Higher profits

Our Guarantee*

Phase Technologies guarantees that LH product lines will meet the IEEE 519-2014 standard when at least 50% of rated current load is maintained. If a system does not comply, Phase Technologies will either offer a suitable fix to bring the panel into compliance or offer a full refund for the purchase price of the panel upon return. (See product warranty for details)

What Are Harmonics?

In electrical systems, harmonics are distortions in current and voltage waveforms. The distortions are mathematically described by voltages and currents at frequencies other than the fundamental frequency of 60 Hz.

What Causes Harmonics?

In electrical systems, harmonics are created by non-linear loads from switching power supplies, VFDs, solid state heater controls, transformers, rectifiers, and other saturated magnetic devices. Often distortions in current produce distorted voltages when the transformers become saturated and the system cannot effectively source the large current surges drawn by the non-linear loads.

The Impact Of Harmonics?

Harmonic distortion generated by standard diode bridge VFDs creates problems for the power utility and other customers on the electrical distribution system. Problems can include overheating of the distribution transformer due to saturation, overheating of conductors, failure of sensitive equipment, and a general degradation of power quality. High voltage transients and voltage unbalance are byproducts of harmonics. Other motors on the system can be damaged when the high voltage transients breakdown winding insulation. Unbalanced voltages increase motor running temperatures and can produce damaging arcing inside shaft bearings.

What Is IEEE519 Compliance?

IEEE 519 is an industry standard that determines allowable limits of voltage and current distortion on utility systems. As the use of VFDs has increased, so have the negative impacts of the harmonics they generate. As a result, more utilities are enforcing compliance with IEEE 519.

See Phase Technologies' Low Harmonic Options

• Low Harmonic Variable Frequency Drives

Phase Converting (240V to 480V)

Three Phase

• Low Harmonic Phase Converters

Phase Perfect® Digital Phase Converter 

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Harmonic Profiles

Total Harmonic Distortion (THD) of LH Series Drives vs. Standard Diode Bridge Drives

In these tests harmonic distortion was reduced by 90-95%.


THD Current = 3.1%

Standard Diode Bridge
VFD w/DC Link Choke

THD Current = 74.9%


THD Current = 5.4%

Standard Diode Bridge
VFD w/DC Link Choke

THD Current = 46%