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Transformer Materials Update Impact; Cost; Environmental; Energy Efficiency. Thursday – November 29, 2007 Omni La Mansion Del Rio Hotel San Antonio, Texas. Technical losses in transformers
Thursday – November 29, 2007
Omni La Mansion Del Rio Hotel
San Antonio, Texas
The dominant no-load loss is core loss, which is associated with the time-varying nature of the magnetizing force and results from hysteresis and eddy currents in the core materials.
Hysteresis losses can be reduced by selecting low core losses material, while eddy currents by reducing lamination thickness. During last fifty years the improving technology of transformer sheets rolling, with techniques to refine the domains of the iron crystals, proper cut, fabrication and assembling techniques reduced unit losses from 3W/kg to less than 1 W/kg in traditional technologies.
(1) the resistive heating losses in the windings due to both load and eddy currents,
(2) stray loss due to leakage fluxes in the windings, core clamps, and other parts,
(3) the loss due to circulating currents in parallel windings and parallel winding strands.
For transformers, the major source of load losses is the I2R losses in the windings. Load losses can be reduced by selecting lower-resistivity materials (such as copper) for the windings, by reducing the total length of the winding conductor, and by using a conductor with a larger cross-sectional area. Eddy currents are controlled by subdividing the conductor into strands and insulating the conductor strands and by conductor shape and orientation. Clearly, this involves a combination of material and geometric options that also depend upon the core dimensions
The saturation level has been increased and together with other technological improvements amorphous cores can now be applicable for three phase units at any size of transformer. Efficiency gain is huge. No load losses can be reduced by additional 70% to 80% compared to best silicon steel reaching levels of 0,065W/kg
Superconducting transformer uses high temperature superconducting materials (HTS) which need to be cooled to the temperature of about minus 200°C. Prototypes and single applications for non distribution business are nothing new. China's Institute of Electrical Engineering have lately demonstrated a three-phase, 630kVA distribution transformer with voltage ratio of 10kV to 400V. It utilizes an amorphous alloy core to further reduce electrical losses over that achieved by the superconductor wires alone. The total energy efficiency of this first device was 98,3%. It is expected that more mature designs will achieve efficiencies as high as 99.9%
There are other solutions to increase transformer efficiency even further like replacing existing conductor material with silver which is the best electrical conductor or new insulation materials which enhance heat transfer. These and other ideas are still in very early R&D stage or simply not practical and not ready for massive deployment.
Magnetic components designers are always looking for improved soft ferromagnetic core materials to increase the efficiency, temperature rating and power density of transformers, motors, generators and alternators, and energy density of inductors. The primary means to increase the transformer’s efficiency is to decrease the loss in the magnetic core material and the I2R or Joulean loss in the windings. The primary means to increase the transformer’s power density is to increase the frequency.
But increasing the frequency without a decrease in the magnetic flux density will increase the core loss. So in most instances, the trade-off between power density, efficiency, and temperature rise comes down to a trade between operating frequency and magnetic flux density of the magnetic core material and current density in the windings. It should be noted that increasing the frequency will also increase the AC I2R loss in the windings.
Why amorphous versus crystalline soft magnets? Amorphous Metals exhibit:
SiFe Steel Transformers
Amorphous vs. SiFe Steel Transformers
Core Loss (W)
DOE outlined the procedural and analytical approaches for the manufacturer impact analysis.
Phase 2, “Industry Cash Flow,” focuses on the industry as a whole. Using publicly available information developed in Phase 1, the Department adapted a generic structure to perform an analysis of the impact of transformer energy conservation standards on the industry cash flow.
Phase 3, the “Sub-Group Impact Analysis,” DOE conducted interviews with several manufacturers. DOE interviewed included small, medium, and large manufacturers providing a representative cross-section of the U.S. distribution
Adopted in March 2006, by European Council, The Energy End-Use Efficiency and Energy Services Directive can be a new challenge to improve energy efficiency also in transformers.