Transformers

Transformers are very efficient devices, but, because they are used in large numbers in the electricity transmission and distribution systems, and because they transfer huge amounts of energy, the cumulative losses are very high – estimated as about one third of total transmission losses.

A study in 2005 indicated that improving energy efficiency of existing European stock of transformers by 40% would result in about 22 TWh energy savings - equivalent to about 9 million tonne of C0₂ equivalent.

For industrial transformers – those within installations rather than on the public network – efficiency is particularly important because they tend to be operated at higher loading where losses are greater. It is important that transformers are specified taking into account the total lifetime operating cost. Transformer losses are adversely affected by harmonic currents, which significantly increase eddy current losses leading to higher working temperatures and severe reduction in life expectancy.

Publications and Software

To see all Electrical Application publications and software click here.

Selecting Energy Efficient Transformers - A Guide for Achieving Least Cost Solutions Energy-efficient transformers can make a valuable contribution to energy savings. Energy savings of about 18.5 TWh of electricity per year could be achieved if all European distribution transformers operating today were replaced by the most energy-efficient transformers available today. An energy-efficient transformer has 50 % lower energy losses than the average transformer installed today.  Energy-efficient transformers usually have lower lifetime costs, despite their higher capital cost, because of the lower cost of losses over their lifetime.  This report from SEEDT, a project carried out under the Intelligent Energy – Europe programme, discusses how to select the transformer with the lowest life time cost. 2008, 32pp.

Power Quality & Utilisation Guide - Application Note 3.5.2 Selection and Rating of Transformers
This Application Note provides the theory and practical guidance on de-rating of power transformers to avoid a reduction in operational lifetime in the presence of harmonic currents. 2006. 8pp.

The Potential for Global Energy Savings from High Efficiency Distribution Transformers
Report concluding that improving the efficiency of distribution transformers in electricity networks around the world can be achieved and will yield substantial net gains for the world's economy. European Copper Institute, 2005, 50pp.

Pub 116 Electrical Energy Efficiency
Life time running costs must be taken into account when designing electrical installations or selecting replacement cables, motors and transformers. Both financial appraisal and technical consideration of electrical energy efficiency of motors, cables, busbars and transformers, with actual case histories showing savings to be made can be found in this book. 1997. 80pp.

Pub 144 Harmonics, Transformers and K-Factors
Transformers used to supply IT equipment and other non-linear loads need to be de-rated to between 60 and 80% of their nominal capacity. This technical note explains why, and how to determine the correct factor. 2000. 6pp. (Out of print).

D12 K-Factor Calculation Software
This software calculates the K-Factor of a load from the harmonic content accordingto US and European practice. The results can be used to select transformers or to determine suitable de-rating factors for transformers. The software requires Windows 95 or higher or NT version 4.0 or higher.