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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

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transformer materials update impact cost environmental energy efficiency

Transformer Materials UpdateImpact; Cost; Environmental;Energy Efficiency

Thursday – November 29, 2007

Omni La Mansion Del Rio Hotel

San Antonio, Texas

Technical losses in transformers
  • Transformers are very efficient electrical machines reaching maximum efficiency at the level of 97.5% to 99.4%. Operating efficiency is smaller because transformers do not operate at maximum efficiency all the time. This maximum efficiency point is at the point where load losses proportional to square of transformer load are equal to the no load losses which are constant and appear all the time when the transformer is energized (usually between 40% and 50% loading).

No load losses

  • No-load losses are those losses required in the excitation of the transformer load losses. They include dielectric loss, conductor loss due to excitation and circulating currents, and core loss.

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.

  • Core losses are dependent upon the excitation voltage and may increase sharply if the rated voltage of the transformer is exceeded. There is also some inverse dependence on core temperature.

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.


Load losses

  • Unlike no-load losses, which are constant and always present, load losses vary with the square of the load current carried by the transformer and include:

(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


Non traditional solutions

  • Amorphous cores are relatively new technology widely used in Japan but also in other Asia regions and in smaller scale in North America . This technology originally developed by Metglas® in the past was more appropriate for single phase and rather small size transformers because of technological difficulties in core assembly. Amorphous metal materials have high electrical resistivity and very little or no magnetic domain definition. Older designs saturated at lower flux, approximately 75% of conventional core flux density that resulted in bigger transformer sizes.

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.



  • To achieve an amorphous structure in a metallic solid, one has to solidify the molten metal before constituent atoms take their positions in a crystalline atomic structure. The required rate for molten-metal cooling is about one million degrees Celsius per second for most of the amorphous metal we are interested in. Therefore mass-produce amorphous metal is in the early stages of development.

Why amorphous versus crystalline soft magnets? Amorphous Metals exhibit:

  • easier magnetization (low coercivity and high permeability)
  • lower magnetic loss (low coercivity, high permeability and high resistivity)
  • faster flux reversal (as a result of low magnetic loss)
  • versatile magnetic properties resulting from post-fabrication
  • heat-treatments and a wide range of adjustable chemical compositions



SiFe Steel Transformers


Amorphous vs. SiFe Steel Transformers

Core Loss (W)

  • 75 to 80% reduction
  • New amorphous transformer core materials with improved performance are being invented.
Transformer standards & regulations
  • There are different regulations and standards for distribution transformers around the world. NEMA TP-1 is American standard which is still under US rule making process. This standard is perceived as not tough enough by major US utilities! Top runner is Japanese scheme based on the principle that today’s technology which is most advanced in efficiency challenge becomes market average in certain period.
EN-50464 is new European standard which classifies transformer no load and load losses.
Existing policy measures
  • European debate on security of supply has indicated large EU energy dependency and the need for seeking measures to reduce it. Increasing energy efficiency and promotion of renewables are today’s answer. These energy policy directions have certain impacts on distribution transformers purchasing decisions;

DOE outlined the procedural and analytical approaches for the manufacturer impact analysis.

  • Phase 1, “Industry Profile,” consisted of preparing an industry characterization, including data on market shares, sales volumes and trends, pricing, employment, and financial structure.

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

Climate change threat led to practical measures in Europe such as introduction of Emission Trading Scheme (ETS).
  • CO2 savings in transformers are the component of ETS. Increasing efficiency of transformers can produce environmental benefits.

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.

Ecodesign directive is another policy measure to improve environmental picture of energy using products.
  • Transformers are not yet subject to this directive but if they were, operation phase of environmental performance (operation phase is responsible for more than 90% of the total of typical transformer environmental impact including production, operation and utilization phases) would justify efforts to make the transformers more efficient.

Conclusion & Strategy

  • TTA monitor and provide input
  • TTA could drive energy efficiency standards instead of waiting for the government to tell them what is practical. This is similar to automotive companies developing fuel efficiency standards with or without government intervention.