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Dry-Type Transformers

Purchasing High-Efficiency Transformers

The selection and purchase of a high-efficiency dry-type transformer can be a complicated process.

You can search a list of dry-type transformer models that meet the requirements of Canada's Energy Efficiency Regulations.

Purchasing Tips

  1. Know your facility's load profile. Every transformer has its own unique efficiency profile based on its load and no-load losses, so a transformer's energy losses will depend heavily on building and equipment usage patterns. Large transformers tend to be heavily loaded, while transformers that serve smaller industrial and commercial customers tend to be more lightly loaded. The better you understand your facility's load profile, the more effectively you will be able to choose the most efficient transformer for your facility.

  2. Consider what type of equipment the transformer will be powering. The efficiencies specified for dry-type transformers are calculated under linear load conditions. Examples of linear loads include lighting and motors. Increasingly, transformers are supplying power to non-linear loads, such as adjustable speed drives, computers and electronic equipment. These non-linear loads produce harmonic distortion that increases transformer losses. If your transformer will be supplying power mainly to computers and office equipment (as opposed to motors and pumps), it may be worthwhile considering the transformer's K rating Transformers with high K ratings are specifically designed to be more efficient with non-linear loads. Bear in mind, however, that transformers with high K ratings can cost up to twice as much as a standard transformer and, depending on your load, they may not be necessary. Manufacturers make transformers with K ratings as high as 13, but a recent survey of dry-type transformers found the average K factor to be only 2.7.

  3. Do not be misled by transformers that are rated at full-load efficiency. It is important to remember that transformers are rarely run at their full-load. In fact, 35 percent is the accepted industry average transformer load. A survey of dry-type transformers actually found the average load factor in manufacturing facilities to be only 14.1 percent. The efficiency of any transformer at this low load is very different from its efficiency at full load.

  4. Do not choose your transformer solely on the lowest temperature rise. Some purchasers believe that choosing a transformer with a low temperature rise will result in an energy-efficient transformer, but this is not always the case. In general, the lower the temperature rise of a transformer, the lower its internal losses, but when manufacturers design a transformer for a low-temperature rise, they often decrease the load losses but increase the no-load losses. This is due to the cooling method, i.e. fans. If a transformer is running at a very low load, this method of selecting a transformer can actually result in choosing a less efficient model.

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