Increasing Efficiency Regulations of Distribution Transformers Requires the Use of Highly Accurate Transformer Loss Measurement Systems

Throughout the world regulatory bodies are focusing more and more on promoting energy efficient distribution transformers that are to be used in the energy transmission and distribution network. According to the analysis conducted by the Superefficient Equipment and Appliance Deployment (SEAD) Initiative, established under the Clean Energy Ministerial and the International Partnership for Energy Efficiency Cooperation, transmission and distribution network losses amount to $61 billion and 700 million tons of greenhouse gas emissions annually. The largest contributor are transmission and distribution power lines with the losses generated by distribution transformers being the second highest source of losses in an electrical network. As a result, mandatory programs have been established in many countries to encourage the implementation of energy-efficient transformers to reduce the energy losses in the distribution network and improve the economic and environmental benefit. Manufacturers are encouraged and/or compelled to improve the efficiency of their designs. These new design efforts must then also be tested to demonstrate their regulatory compliance, which requires the use of highly accurate loss measurement systems. The last thing the manufacturers would want is to have high measurement uncertainties affect their high efficiency design efforts!

In 2005 the estimated transmission and distribution network losses in North America totaled 305 TWh or approx. 7.1%. Distribution transformers are more easily replaced compared to power lines, and their efficiency can also be easily measured using loss measurement systems. The Lawrence Berkeley National Laboratory estimates that by the year 2030 75 TWh of electricity and 30 million metric tons of CO2 emissions can be saved annually worldwide by adopting efficiency regulations and manufacturing higher efficiency design distribution transformers. Effective in 2016 the US Department of Energy introduced new mandatory, minimum level performance requirements (MEPS) for distribution transformers depending on kVA rating and type (i.e., oil-filled or dry-type). All liquid-filled 1 and 3-phase transformer designs are required to increase their efficiency ratings compared to the MEPS levels in 2010. Depending on the type of liquid-filled transformer, the efficiency increases amount to anywhere between 0.02% to 0.3%. 1 and 3-phase dry-type transformers will also see efficiency increases by up to 0.63% depending on the kVA rating. These design changes will ultimately help to further reduce unnecessary losses and greenhouse gas emissions.

Implementing efficiency design changes will also require for testing equipment to meet the demand for higher accuracy testing. For example, the EU implemented Directive 2009/125/EC with regard to small, medium, and large power transformers to improve environmental performance of energy related products through better design. Part of this directive has called for different tiers to be reached over the years. In 2021 the Tier 2 EcoDesign must be reached, which will no longer allow positive loss tolerance. The figure below shows that testing equipment will be required to be highly accurate in order for the transformers to meet the design directives. Uncertainty of the test equipment will be a major factor that transformer manufacturers will have to deal with!

Manufacturers of transformer designs with excessive losses will be exposed to penalties if they cannot prove that their designs are within the new directives. Therefore, a reliable loss measurement system with very low uncertainties will provide confidence to the manufacturers that their designs are meeting the directives and no expensive penalties are incurred adding to overall product costs.

What are the losses measured in transformers?

All types of transformers will experience losses and the objective is to reduce these as much as possible. These losses can be classified into load losses and no-load losses and the total losses within the transformer are the sum of the load and no-load losses.

Load Losses:

Load losses are developed within the transformer when rated current at rated frequency is applied to the transformer with the opposite winding shorted. The losses are made up of ohmic losses of the windings and internal connections, as well as the stray losses caused by leakage fields in the windings and the mechanical parts.

No-Load Losses:

No-load losses consist of core losses, winding losses, and insulation losses, which gives information on the defects within a core such as core short circuits or saturation. In general the dielectric and joule losses can be neglected, as they are several magnitudes lower than the iron losses.

Advantages of the TMS 580 Transformer Loss Measuring System

Measurement of transformer losses is an indispensable quality verification process to guarantee that the transformer design meets the efficiency directives in order to improve the economics of energy delivery and reduce the environmental impact of greenhouse gas emissions. The TMS 580 is specially designed and developed for highly accurate measurements of power losses in transformers. The accuracy of the measurements is up to 0.10% for voltage, up to 0.11% for current, and up to 0.17% at a power factor of cos φ = 1.000 for power.


  • Load losses measurement
  • No-load losses measurement
  • Power measurement during Heat run
  • Voltage measurement during Induced voltage test
  • Zero sequence measurement to identify phase sequence impedance
  • Wattmeter function to perform quick and easy measurements without any calculations
  • Self-check to calibrate all ranges of voltage and current channels


  • High measuring accuracy of maximum ±0.35% of the indicated power at a typical frequency of 60 Hz and a power factor of 0.05.
  • The instrument transformers of the TMS 580 are specially designed to ensure very small phase angle errors, thus making additional error correction redundant. This ensures accurate measurements on large power transformers with very small power factor.
  • Short throughput times due to the elimination of instrument transformer rewiring, remote range selection, and computer aided processing.
  • Assured documentation quality with a precise test report, which is generated automatically at the end of a measurement.
  • Easy to use windows-based interface reduces the learning process and minimizes faulty operations.

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