The Phenomenon of Odd Harmonics
Electronic equipment today is powered by SMSPs (switch mode power supplies) that convert AC current to DC current. SMSPs use rectifiers and capacitors drawing current in sharps bursts which distorts the sinusoidal waveform. It is now non-linear. Non-linear loads, are rich in odd harmonics (3, 5, 7, etc.), which are multiples of the fundamental 60 Hertz frequency. The major components of harmonic currents in switched mode power supplies are the third and fifth harmonics. The 3rd harmonic current (180Hz) due to the design of the 3-phase system, is additive in the neutral and can result in a neutral current twice the phase current, even in a balanced system.
*Harmonics Limited is now a part of Jefferson Electric
How Harmonics Affect Transformers
When odd-harmonic currents are present, winding losses increase. The I2R, conductor losses, are higher because harmonics increase the current. Stray losses in windings also increase losses due to additional eddy currents circulating within the conductors. The combination of these additional losses generate excess heat in the transformer coils. Transformer insulation systems are designed to accommodate temperature increases due to normal stray losses. However, when required to carry nonlinear loads, the heat generated may exceed the designed rating, reducing the life of the transformer and creating the possibility of premature failure. Read this article for additional information.
De-rating is Not the Answer
De-rating a traditional linear transformer to compensate for heat build-up requires higher installation costs and provide poor energy efficiency due to increased core losses.
Solutions for Harmonics in the Power System
The Harmonic Suppression System (HSS™) eliminates the harmful 3rd harmonic current generated by the operation of electronic power supplies. An HSS eliminates the 3rd harmonic current, removing it from the distribution system.
Patented HSS technology allows transformers to be sized to the load. There is no need to de-rate or oversize panels, reducing installation costs and energy consumption and increasing equipment life. ROI can be less than 24 months.
For additional information see these articles:
SysteMax™ is a stand alone 3rd harmonic suppression filter that is connected to the neutral of an existing distribution transformer. It is sized to the transformer (15 kVA to 1,000 kVA).
TransMax™ is a SysteMax filter incorporated in an enclosure with a high efficiency transformer. The basic transformer is 480V primary, 208Y/120V secondary, with either copper or aluminum windings, 115°C rise and electrostatic shielding. Options include 80°C rise, low noise (-3dB) and 208V primary. Enclosure type is UL/NEMA Type 1, ANSI–61 gray paint. Standard sizes range from 30 kVA to 500 kVA.
GenMax™ is a passive, tuned harmonic suppression system for generators. This new technology allows generators with different winding pitches to operate at full capacity by reducing circulating 3rd harmonic ground currents. For additional information, please these articles: EGSA Paper, Magee Case Study and Zook Case Study
Please contact us for more information on this product line.