Costly 50 Hz transformers

Dear Control Engineering:

Most of the projects our company builds are used in North America, but we sometimes have to adapt equipment for overseas applications. Why is it that transformers capable of operating in a 50 Hz environment cost more than those for domestic 60 Hz operation? Is this a marketing ploy or is there a real justification for the cost difference?

We put this question to Steven Ensign at Ensign PowerVolt, a producer of transformers and power supplies. He answers:

In customer transformer specifications, it is frequently assumed that the transformer will operate at 60 Hz, and Ensign often must ask if the customer also requires 50 Hz operation. This is more than simply our version of, "Do you want fries with that?" The ability to operate at 50 Hz impacts the transformer’s performance as well as its cost. Sometimes it also determines the degree of safety the transformer can provide.

Here’s why: Back in high school physics class we observed the circular patterns, called magnetic flux lines made by sprinkling iron filings over a magnet. 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 has a limit on how many flux lines it can handle; and
2) The lower the operating frequency the more flux lines that are generated.

Operating a transformer at 50 Hz generates 20% more flux lines than at 60 Hz. As the number of flux lines approaches the magnetic material’s limit, the heat in both the magnetic core and the internal 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 50 Hz will simply run cooler at 60 Hz. But one designed only for 60 Hz may overheat at 50 Hz.

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 high-grade core materials when they are not required results in transformers that are over-designed and not competitively priced.

So, if a transformer will ever see 50 Hz current for the European, South American, UK, Japanese, or other Asian markets, the capability to do so must be designed in from the beginning. But if it will only see 60Hz, there is no sense in adding the unnecessary cost.

–Edited by Peter Welander, process industries editor