Specifying a Transformer: Why does 50Hz make such a difference?

-April 23, 2009

I was recently contacted by Steve Ensign, a design engineer at Ensign Corporation,  designers and manufacturers of transformers and power supplies.  Steve wanted to point out the importance of specifying initially if your system will need to run at 50Hz in addition to 60Hz.  The decision to include or exclude 50Hz capability impacts the transformer’s performance as well as its cost, and can also affect the operating safety margin.

Magnetic flux lines from WikipediaBack in high school physics we observed magnetic flux lines traced by iron filings in a magnetic field. Says Steve, “An energized transformer is an electromagnet and therefore creates similar magnetic flux line patterns.  When dealing with flux lines and transformers, two laws of physics are particularly significant:

1) Each magnetic material which could be used in a transformer’s core has a limit on how many flux lines it can handle

2) The lower the operating frequency the more flux lines that are generated. Operating a transformer at 50Hz generates 20% more flux lines than at 60Hz. As the number of flux lines approaches the magnetic material’s limit, the heat in both the transformer’s core and its coil wires increases, and under certain circumstances, unpredictably so. This can result in a transformer that exceeds safe temperature levels. Therefore, a transformer designed to run at 50Hz will simply run cooler at 60Hz. But one designed only for 60Hz may overheat if subjected to 50Hz.

“In order to accommodate 50Hz operation, the transformer must employ a magnetic core material that can handle the added flux lines. Such materials are readily available, but they are significantly more costly than the "normal" core materials. Using such high-grade core materials when they are not required results in transformers that are over-designed  and probably overpriced.

“So, if a transformer will ever see 50Hz (for the European, South American, UK, Japanese, or other markets), the capability to do so must be designed in from the beginning. But if it will not see 50Hz, there is no sense in adding the unnecessary cost.”

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